ALBERT

Description: Abstract This paper presents a new, global database of lunar impact craters, estimated to be a complete census of all craters with diameters larger than 1–2 km. The database contains over 2 million craters, making it larger in number than any previously published lunar effort by more than a factor of 10. Of those craters, 1.3 million have diameters ≥1 km, 83 thousand ≥5 km, and 6972 ≥20 km. How the database was constructed along with the reliability of features are described in detail. Comparisons are made with past published databases, demonstrating good agreement for crater size and location. An ellipticity analysis is conducted, illustrating there is no dominant direction for elliptical crater orientation based on location, diameter range, or ellipticity amount, consistent with randomness for craters ≥10 km. A spatial density analysis is described, comparing the spatial density of small versus large craters, and numerous observations about the nonuniformity of the size distributions of craters across the Moon are made. The spatial density is also used in a discussion about kilometer‐scale secondary impact craters and clearly shows that they dominate the crater population in some areas of the lunar surface. While this database is complete as‐is, future work will expand it and fix errors that might be identified, so it is strongly recommended that interested individuals contact the corresponding author to be alerted to updates.

Description: Abstract The role of micrometeorite bombardment in space weathering on asteroid surfaces was studied using a 2 MV Van–De–Graaff accelerator. About 90000–100000 micron– to sub–micron sized copper particles with a mass– and velocity distribution similar to the interplanetary dust population, were fired onto the surfaces of polished Allende CV3 chondrite and eucrite NWA 6966 samples at speeds between km s−1. We find a clear relationship between micro–particle bombardment, infrared reflectance decrease, and overall spectral reddening. Differences in impact effects due to variable particle speed, size and structure are observed. Some Cu–particles form large clusters that break up upon impact and disperse. Other impactors leave imprints on the surface, implant or generate typical craters with rims and spallation features. Very small, fast particles generate small craters without spallation or significant crater rim. Mid–IR–spectra (bulk– and microscopic measurements of individual components), 3D–Laser microscopic images and XRD–spectra from the processed and unprocessed samples were collected. Mid–IR–spectra (700–6000 cm−1) over the entire sample surface, show overall darkening of features. Microscopic IR–spectra show the damage seen as reflectance decrease and spectral reddening, which is variable in the μ–range, depending on impact density and target properties (mineralogic composition). The fine–grained Allende matrix with predominantly Fe–rich olivine seems less affected than coarse–grained chondrules with Mg–rich silicates, where darkening can reach 60%. XRD–analysis also suggests chemical and crystallographical differences in the bombarded sample, due to impact shock.

Description: Abstract The processes of alteration of airless bodies exposed to the space environment are referred to be as ‘space weathering’. Multiple agents contribute generally to space weathering, to an extent that depends on the specific location of the surface within the Solar System. Typical space weathering agents encountered in the Solar System are: solar radiation, solar wind and cosmic rays, magnetospheric plasma (for example, at Jupiter or Saturn), and cosmic dust. The effect of space weathering is generally assessed by measuring the surfaces optical properties, for example by near‐infrared (IR) spectroscopy. The alteration of the surfaces is due to a cumulative effect over time of all agents. We investigate in this paper the contribution of micro‐meteoroid (dust) bombardment on different asteroids, by using the Micrometeoroid Environment Model (IMEM) for the interplanetary dust populations (IDPs), and a simplified model of Interstellar Dust (ISD) dynamics. We quantify, for different representative asteroids (Main Belt and NEOs), the particle cumulative flux, mass flux, impact velocity and the kinetic impact energy deposited. This work is primarily intended to support laboratory work investigating the effect of energy deposition onto sample surfaces, as well as astronomical observations of optical properties of asteroid surfaces.

Description: Abstract We present a comprehensive global catalog of the geomorphological features with clear or potential relevance to subsurface ice identified during the Dawn spacecraft's primary and first extended missions at Ceres. We define eight broad feature classes and describe analyses supporting their genetic links to subsurface ice. These classes include: relaxed craters; central pit craters; large domes; small mounds; lobate landslides and ejecta; pitted materials; depressions and scarps; and fractures, grooves, and channels. Features in all classes are widely distributed on the dwarf planet, consistent with multiple lines of observational evidence that ice is a key component of Ceres' crust. Independent analyses of multiple feature types suggest rheological and compositional layering may be common in the upper ~10 km of the crust. Clustering of features indicates that ice concentration is heterogeneous on nearly all length scales, from ~1 km to 100s of km. Impacts are likely the key driver of heterogeneity, causing progressive devolatilization of the low and mid‐latitude crust on billion‐year timescales, but also producing localized enhancements in near surface ice content via excavation of deep ice‐rich material and possible facilitation of cryomagmatic and cryovolcanic activity. Impacts and landslides may be the dominant mechanism for ice‐loss on modern Ceres. Our analysis suggests specific locations where future high‐resolution imaging can be used to probe (1) current volatile loss rates and (2) the history of putative cryomagmatic and cryovolcanic features. The Cerean cryosphere and its unique morphology promise to be a rich subject of ongoing research for years to come.

Description: Abstract Northwest Africa (NWA) 11042, originally classified as a primitive achondrite with no chondritic relicts, is rather a unique L‐melt rock. It is a severely shocked, igneous‐textured ultramafic rock composed of euhedral to subhedral olivine (Fa25.1±0.5) and pyroxenes (Low‐Ca pyroxene Fs20.7±0.8Wo4.2±1.0, and Ca‐rich pyroxene Fs11.5±0.5Wo37.6±1.2) with interstitial albitic plagioclase (Ab80.7±1.7Or5.0±0.7) that has been completely converted to maskelynite. Mineral compositions are similar to those of equilibrated L chondrites. Melt pockets are scattered throughout the sample, containing high‐pressure minerals including ringwoodite, wadsleyite, jadeite, and lingunite. Merrillite and apatite in NWA 11042 contain significantly higher REE abundances than those of ordinary chondrites, indicative of igneous fractional crystallization. In situ U‐Pb dating of apatite in NWA 11042 reveals an upper intercept age of 4479±43 Myr and a lower intercept age of 465±47 Myr on the normal U‐Pb concordia diagram. The upper intercept age recorded the time when NWA 11042 initially crystallized. This age is much younger than when the decay of short‐lived nuclides (e.g., 26Al) would act as a major heat source, suggesting melting and crystallization of NWA 11042 could be otherwise triggered by an impact event. The lower intercept age represents a reset age due to a later impact event, that is in coincidence with the disruption event of L chondrite parent body at ~470 Myr. NWA 11042 is an excellent example to link igneous‐textured meteorites with a chondritic parent body through shock‐induced melting.

Description: Potential increases in the risk of extreme weather events under climate change can have significant socio‐economic impacts at regional levels. These impacts are likely to be particularly high in South Asia where Bangladesh is one of the most vulnerable countries. Regional climate models (RCMs) are valuable tools for studying weather and climate at finer spatial scales than are typically available in global climate models. Quantitative assessment of the likely changes in the risk of extreme events occurring requires very large ensemble simulations due to their rarity. The weather@home setup within the climateprediction.net distributed computing project is capable of providing the necessary very large ensembles at regionally higher resolution, but has only been evaluated over the South Asia region for its representation of seasonal climatological and monthly means. Here, we evaluate how realistically the HadAM3P‐HadRM3P model setup of weather@home can reproduce the observed patterns of temperature and rainfall in Bangladesh with focus on the modelled extreme events. Using very large ensembles of regional simulations, we find that there are substantial spatial and temporal variations in rainfall and temperature biases compared with observations. These are highest in the pre‐monsoon, which are largely caused by timing issues in the model. Modelled mean monsoon and post‐monsoon temperatures are in good agreement with observations, whereas, there is a dry bias in the modelled mean monsoon rainfall. The rainfall bias varies both spatially and with the dataset used for comparison. Despite of these biases, the model simulated temperature and rainfall extremes in summer monsoon over Bangladesh are approximately representative of the observed ones. At the wettest parts of north‐east Bangladesh, rainfall extremes are underestimated compared to GPCC and APHRDITE but are within the range of CPC observations. Therefore, the weather@home RCM, HadRM3P can be used to study the changing risks of extreme weather events over Bangladesh.

Description: The mobility of landslides on Mars is studied based on a database of 3,118 events. To establish the volume of the landslides for the whole dataset based on the deposit area, a new volume-area relationship based on a representative dataset of 222 landslides is used. Plotting the H/L ratio between fall height H and runout L versus volume, landslide mobility is analyzed and compared with existing empirical relationships for Martian and terrestrial landslides. Analyzing the mobility in terms of normalized residuals, i.e., the relative deviation of the H/L ratio from the dataset best-fit line, mobility is found to depend on both the landslide location on Mars, and landslide typology. This allows us to identify four different types of high mobility (hypermobile) landslides. Three classes of high mobility landslides are associated respectively to meteoroid impact, the Olympus Mons aureoles, and landslides with Toreva-block failure style, and their mobility can be explained by the peculiar flow mechanics. The fourth class includes landslides associated with isolated craters, those in the regions wetted by the putative Oceanus Borealis, and the ones at high latitudes. We suggest that the common factor behind all the hypermobile landslides of this fourth kind is the presence of ice. This is confirmed by our data showing that landslides increase in mobility with latitude. The latitudinal trend mirrors the distribution of ice as detected by radar, neutron probes, and the presence of glacial and layered ejecta morphologies. Because the overall landslide distribution supports the presence of ice-lubricated conditions, two ice lubrication models are presented showing how ice melting within or underneath the landslides could enhance mobility. By proper analysis in terms of apparent friction residuals, we find that the mobility of landslides in Valles Marineris with the largest landslide concentration is lower than average. We explain this circumstance partly from the smaller role of ice in equatorial Valles Marineris, and partly because the collapses from high slope relief imply high-speed impact with the floor valley confinement, loss of momentum, and decrease in mobility. Environmental consequences imply that the present subsurface ice distribution may have been persistent throughout the Amazonian period.

Description: ABSTRACT An analytical study was conducted to assess the long-term influence, role, and impacts of El Niño-Southern Oscillation (ENSO) on Puerto Rico's precipitation patterns and significant moisture deficits (droughts). Detection and attribution was addressed by evaluating local rainfall measures and ENSO-related data to (1) detect ENSO signals and patterns, (2) quantify the magnitude of any impacts, and (3) determine if ENSO may be an important factor for local prediction of future droughts. Data were evaluated at different time periods and two spatial scales (island-wide and internal climate regions of Puerto Rico). Although a signal was detected, it was weak, in both directions, varied regionally, and has inconsequential impacts. No evidence was found for a major control by ENSO over local monthly, seasonal, and yearly rainfall for any climate regions on the island. These results indicate that ENSO is not a main factor causing droughts in Puerto Rico for the study period and thus should not be a factor in predicting the potential for local dry periods or large precipitation deficits in the future. Any presumed teleconnections between Puerto Rico's dry periods and ENSO are not based on current climatological evidence. Thus, local drought prediction efforts should be focused on finding major causes of local rainfall variation other than ENSO. ENSO's signal was detected in Puerto Rico using different methods but actual impacts on rainfall for the past century are minimal to none at any time and spatial scales.

Description: The lunar cratering record provides valuable information about the late accretion history of the inner Solar System. However, our understanding of the origin, rate, and timing of the impacting projectiles is far from complete. To learn more about these projectiles, we can examine crater size-frequency distributions (CSFDs) on the Moon. Here, we re-investigate the crater populations of 30 lunar basins (≥ 300 km) using the buffered non-sparseness correction (BNSC) technique, which takes crater obliteration into account, thus providing more accurate measurements for the frequencies of smaller crater sizes. Moreover, we revisit the stratigraphic relationships of basins based on N(20) crater frequencies, absolute model ages, and observation data. The BNSC-corrected CSFDs of individual basins, particularly at smaller crater diameters are shifted upwards. Contrary to previous studies, the shapes of the summed CSFDs of Pre-Nectarian (excluding South Pole-Aitken Basin), Nectarian (including Nectaris) and Imbrian (including Imbrium) basins show no statistically significant differences, and thus provide no evidence for a change of impactor population.

Description: ABSTRACT The sub-monthly intra-seasonal 8–24-day period (SIS8-24) timescale variability of the summer (1 November to 31 March) rainfall over South America (SA) under distinct inter-annual (IA) backgrounds was analysed using the Tropical Rainfall Measure Mission (TRMM) based daily total precipitation data for the 1998–2012 period. The IA backgrounds refer to the El Niño (EN) and La Niña (LN) years. First, the summer daily precipitation anomaly fields were subject to the empirical orthogonal function (EOF) analysis. Using the first and the second principal component time series filtered at the SIS8-24 timescale, positive and negative events were selected. The first SIS8-24 mode features a precipitation anomaly dipole with centres over southeastern SA (SESA) and central and eastern tropical SA both extending southeastwards into the adjacent Atlantic Ocean. The second mode features a precipitation anomaly pattern similar to that previously documented for the oceanic South Atlantic convergence zone (SACZ). The SIS8-24 precipitation anomaly patterns for the positive (negative) events show differences in the anomaly intensities between EN and LN years, but with almost the same locations of the anomaly centres. These differences result from the variability inter-SIS8-24 events, as indicated by the distinct paths of the SIS8-24 Rossby wave train patterns in the subtropics, although they are regionally locked over tropical SA. The relation between the SIS8-24 and IA variabilities might occur through variations in the Rossby wave train patterns. The Rossby wave trains of both timescales, depending on their phases, reinforce or weaken the rainfall anomalies over SA, in such a way that the rainfall anomalies over SA show similar patterns but with distinct magnitudes for EN and LN composites. The South American precipitation responses to the combined SIS8-24 and IA variability timescales stratified according to the IA backgrounds have not been studied before and might be useful for operational forecasting services. The sub-monthly intra-seasonal 8–24-day period (SIS8-24) timescale variability of the summer (1 November to 31 March) rainfall over South America (SA) under distinct inter-annual (IA) backgrounds was analysed using the Tropical Rainfall Measure Mission (TRMM) based daily total precipitation data for the 1998–2012 period. The IA backgrounds refer to the El Niño (EN) and La Niña (LN) years. The first mode features a precipitation anomaly dipole with centres over southeastern SA (SESA) and the second mode features a precipitation anomaly pattern similar to that previously documented for the oceanic South Atlantic convergence zone (SACZ).

Description: ABSTRACT Observational analyses of changing climate extremes over the West Africa region have been limited by the availability of long and high-quality datasets. To help address this gap, a climate extremes indices workshop was held in the Gambia in December 2011 with participants from 14 West African countries. The resulting analysis utilized 15 annual indices derived from observed daily temperatures and 10 annual indices derived from observed daily precipitation. The analysis was conducted for 166 meteorological stations in 13 countries for 2 periods: 1960–2010 and 1981–2010. The analyses of trends in the annual mean temperature indices have identified statistically significant increases of 0.16 °C/decade and 0.28 °C/decade for mean annual maximum and mean annual minimum temperatures, respectively, averaged over all available land stations in the region during the last 50 years. The seasonal-temperature-related indices show significant patterns of warming in all seasons. The annual mean of daily minimum temperature has increased more than the annual mean of daily maximum temperature leading to a decreasing trend in the diurnal temperature range. Warm days and warm nights have become more frequent, and cold days and cold nights have become less frequent. The analyses of precipitation-based indices indicate spatially non-coherent changes throughout the study area with few statistically significant trends over the longer period. Exceptions to this are the simple daily intensity index and maximum 5-day precipitation, which show significant increasing regional trends over both the shorter and longer periods. Additionally, over the recent period (1981–2010) most of the precipitation related indices show significant trends towards wetter conditions. However, this period of increased rainfall follows a decade of significantly drier conditions in the region – it is not clear whether the recent upward trends reflect the ‘recovery’ from this long drought period or represents a long-term response to warming. Climate extremes indices were derived from daily temperature and precipitation data from 166 observing stations in 13 West African countries, and combined to provide a regional assessment of changing extremes for 1960–2010 and 1981–2010. Statistically significant warming trends indicate more frequent warm days and nights and less frequent cold days and nights. Precipitation-based indices indicate weak spatial patterns with few significant trends over 1960–2010, but over 1981–2010 show significant trends towards wetter conditions.

Description: Aeolian processes have likely been the predominant geomorphic agent for most of Mars’ history and have the potential to produce relatively young exposure ages for geologic units. Thus, identifying local evidence for aeolian erosion is highly relevant to the selection of landing sites for future missions, such as the Mars 2020 Rover mission that aims to explore astrobiologically-relevant ancient environments. Here, we investigate wind-driven activity at eight Mars 2020 candidate-landing sites to constrain erosion potential at these locations. To demonstrate our methods, we found contemporary dune-derived abrasion rates were in agreement with rover-derived exhumation rates at Gale crater and could be employed elsewhere. The Holden crater candidate site was interpreted to have low contemporary erosion rates, based on the presence of a thick sand coverage of static ripples. Active ripples at the Eberswalde and southwest Melas sites may account for local erosion and the dearth of small craters. Moderate-flux regional dunes near Mawrth Vallis were deemed unrepresentative of the candidate site, which is interpreted to currently be experiencing low levels of erosion. The Nili Fossae site displayed the most unambiguous evidence for local sand transport and erosion, likely yielding relatively young exposure ages. The down-selected Jezero crater and northeast Syrtis sites had high-flux neighboring dunes and exhibited substantial evidence for sediment pathways across their ellipses. Both sites had relatively high estimated abrasion rates, which would yield young exposure ages. The down-selected Columbia Hills site lacked evidence for sand movement and contemporary local erosion rates are estimated to be relatively low.

Description: A simplified model setup has been used in atmospheric general circulation models (AGCMs), to clarify the fluid dynamical process of terrestrial planets. In the present work, the research aim is to ascertain the dynamical effects of polar indirect circulation on superrotation and multiple equilibrium states in Venus-like planets. The model setup previously used for Venus AGCM intercomparison is applied to the Model for Interdisciplinary Research On Climate (MIROC) AGCM, and the horizontal resolution and initial conditions are altered in the long-term experiments. The structures of general circulation and planetary-scale waves in the T42 (Truncation wavenumber 42) experiment are similar to those in the T63 experiment. In the presence of the polar indirect circulation, the superrotational flow weakens in the cloud layer and its momentum is transported toward the lower atmosphere at high latitudes. In contrast, in the T21 experiment, because the polar indirect circulation is not fully resolved, the vertical momentum transport due to the indirect circulation is ineffective in the lower atmosphere, and thus the cloud-top superrotational flow becomes greater than those in the higher-resolution experiments. The multiple equilibrium states caused by different initial zonal flows appear in the T21 experiments, although they are not seen in the experiments of T42 and higher. Thus, the polar indirect circulation in the Gierasch–Rossow–Williams mechanism weakens the superrotational flow in the cloud layer and breaks the steady-state multiplicity of the general circulation.

Description: ABSTRACT One of the major obstacles to using numerical weather prediction models for guidance on mitigating urbanization's impact on local and regional climate is the lack of detailed and model ready morphological data at urban scale. The World Urban Database and Access Portal Tool (WUDAPT) is a recent project developed to extract climate relevant information on urban areas, in the form of local climate zones (LCZs), out of remote sensing imagery. This description of the urban landscape has been tested and used for parameterization of different urban canopy models (UCM) for mesoscale studies. As detailed information is usually bounded within cities' centres, crowdsourced and remote sensing data offer the possibility to move beyond the old barriers of urban climate investigations by studying the full range of variation from the urban core to the periphery and its related impacts on local climate. Thus, for this study we sought to compare the relative impact of using the WUDAPT methodology versus a simplified definition of the urban morphology extracted out of detailed GIS information to initialize a regional weather model and compare the output against official and crowdsourced weather station networks. A case study over Vienna, Austria was conducted using the weather research forecasting (WRF) model, coupled with the building effect parameterization and building energy models (BEP–BEM) in five distinct seasonal periods. Results demonstrated that using detailed GIS data to derive morphological descriptions of LCZs for mesoscale studies provided only a marginal overall improvement over using the default WUDAPT parameters based on the ranges proposed by Stewart and Oke (2012). The findings also highlighted the importance of developing techniques that are better at capturing the morphological heterogeneity across the entire urban landscape and thus improve our understandings of UCM performance over urban areas. A case study over Vienna, Austria was conducted using the Weather Research Forecasting (WRF) model, coupled with the building effect parameterization and building energy models (BEP–BEM) in five distinct seasonal periods. Results demonstrated that using detailed morphological descriptions of LCZs for mesoscale studies provided only a marginal overall improvement over using the default WUDAPT parameters. The findings also highlighted the importance of developing techniques that are better at capturing the variation of urban morphology and thus improve UCM performance over urban areas.

Description: ABSTRACT Based on historical and RCP8.5 experiments, along with 25 Coupled Model Intercomparison Project Phase 5 (CMIP5) models, we evaluate the skills of the CMIP5 models in simulating the subtropical westerly jet (SWJ) and its effect on the projected summer rainfall over central Asia (CA). The historical experiments show that 23 models can well simulate the changes in the position and strength of the SWJ. Further analysis finds that 21 models can capture the relationship between the SWJ position change and summer rainfall over the domain of 55–85°E and 35–50°N and 17 models can capture the relationship between the SWJ strength change and summer rainfall over the domain of 55–75°E and 45–55°N, where 15 models can capture the relationships between both SWJ strength and position change with summer rainfall. Based on the SWJ change among the 15 models, except for the HadGEM2-CC model, the 500 hPa winds of the rest 14 models well match the summer rainfall over CA. So the 14 models are used to do next analysis. In the last 50 years of the 21st century, only the inmcm4 model presents the change in the SWJ strength, and the rest 13 models present the changes in the SWJ position. Among above 13 models, 10 models maintain the relationships between the SWJ position change and summer rainfall over the domain of 55–85°E and 35–50°N into the future. Under the background of global warming, the changes in the SWJ position are well related to the sea surface temperatures (SSTs) over the Indian Ocean in the future. The SST warming over the Indian Ocean results in the South Asian summer monsoon weakening, corresponding to an anomalous anticyclone over the low-level troposphere of the monsoon regions; this situation results in an anomalous cyclone at the upper level of the troposphere of the northwestern flank of the monsoon heating regions due to Matsuno–Gill-type responses, which favour the SWJ axis shifting further south. In addition, we also compare the current projected summer rainfall over CA from our selected models with other selected previous models using different methods. The ensemble results show that more summer rainfall occurring in most of Kazakhstan and Xinjiang Province of northwestern China is more likely in the future; in the rest of the countries of CA, there are uncertainties regarding future rainfall changes. The first two leading EOF modes of the summer zonal wind anomaly at 200 hPa over 25–55°N, 40–80°E for 1961–2004 in (a) and (b). The normalized principal component (PC) corresponding to the leading modes of EOF1 (c) and EOF2 (d).

Description: There is strong evidence that Mercury's polar deposits are water ice hosted in permanently shadowed regions. In this study, we present new Arecibo radar observations of Mercury's south pole, which reveal numerous radar-bright deposits and substantially increase the radar imaging coverage. We also use images from MESSENGER's full mission to determine the illumination conditions of Mercury's south polar region at the same spatial resolution as the north polar region, enabling comparisons between the two poles. The area of radar-bright deposits in Mercury's south is roughly double that found in the north, consistent with the larger permanently shadowed area in the older, cratered terrain at the south relative to the younger smooth plains at the north. Radar-bright features are strongly associated with regions of permanent shadow at both poles, consistent with water ice being the dominant component of the deposits. However, both of Mercury's polar regions show that roughly 50% of permanently shadowed regions lack radar-bright deposits, despite some of these locations having thermal environments that are conducive to the presence of water ice. The observed uneven distribution of water ice among Mercury's polar cold traps may suggest that the source of Mercury's water ice was not a steady, regular process but rather that the source was an episodic event, such as a recent, large impact on the innermost planet.

Description: ABSTRACT Quantile estimates are generally interpreted in association with the return period concept in practical engineering. To do so with the peaks-over-threshold (POT) approach, combined Poisson-generalized Pareto distributions (referred to as PD-GPD model) must be considered. In this article, we evaluate the incorporation of non-stationarity in the generalized Pareto distribution (GPD) and the Poisson distribution (PD) using, respectively, the smoothing-based B-spline functions and the logarithmic link function. Two models are proposed, a stationary PD combined to a non-stationary GPD (referred to as PD0-GPD1) and a combined non-stationary PD and GPD (referred to as PD1-GPD1). The teleconnections between hydro-climatological variables and a number of large-scale climate patterns allow using these climate indices as covariates in the development of non-stationary extreme value models. The case study is made with daily precipitation amount time series from southeastern Canada and two climatic covariates, the Arctic Oscillation (AO) and the Pacific North American (PNA) indices. A comparison of PD0-GPD1 and PD1-GPD1 models showed that the incorporation of non-stationarity in both POT models instead of solely in the GPD has an effect on the estimated quantiles. The use of the B-spline function as link function between the GPD parameters and the considered climatic covariates provided flexible non-stationary PD-GPD models. Indeed, linear and nonlinear conditional quantiles are observed at various stations in the case study, opening an interesting perspective for further research on the physical mechanism behind these simple and complex interactions. Using statistical tools like the cross-wavelet analysis illustrated in the figure, common features of variability are found between precipitation extreme events and the Artic Oscillation index at the Upper Stewiacke station located in Nova Scotia (Canada). Using this index as covariate, we developed non-stationary Poisson-generalized Pareto models, which allow observing conditional quantiles with concave form. The proposed models are more flexible than classical extreme value non-stationary models which often used prior assumption of linear dependence.

Description: ABSTRACT It is generally agreed that models that better simulate historical and current features of climate should also be the ones that more reliably simulate future climate. This article describes the ability of a selection of global climate models (GCMs) of the Coupled Model Intercomparison Project Phase 5 (CMIP5) to represent the historical and current mean climate and its variability over northeastern Argentina, a region that exhibits frequent extreme events. Two types of simulations are considered: Long-term simulations for 1901–2005 in which the models respond to climate forcing (e.g. changes in atmospheric composition and land use) and decadal simulations for 1961–2010 that are initialized from observed climate states. Monthly simulations of precipitation and temperature are statistically evaluated for individual models and their ensembles. Subsets of models that best represent the region's climate are further examined. First, models that have a Nash–Sutcliffe efficiency of at least 0.8 are taken as a subset that best represents the observed temperature fields and the mean annual cycle. Their temperature time series are in phase with observations ( r 〉 0.92), despite systematic errors that if desired can be corrected by statistical methods. Likewise, models that have a precipitation Pearson correlation coefficient of at least 0.6 are considered that best represent regional precipitation features. GCMs are able to reproduce the annual precipitation cycle, although they underestimate precipitation amounts during the austral warm season (September through April) and slightly overestimate the cold season rainfall amounts. The ensembles for the subsets of models achieve the best evaluation metrics, exceeding the performance of the overall ensembles as well as those of the individual models. The northeast region of Argentina present hydro-climatic variability at various time scales and undergoes changes in extreme events that could be exacerbated in the coming decades. Reliable projections of future climate require models that adequately represent the regional climate system. This paper evaluates the ability of 27 global climate models (GCMs) of the Coupled Model Intercomparison Project Phase 5 (CMIP5) to simulate the observed climate and selects a subset of 9 models for temperature and 7 models for precipitation. The multi-model ensembles using selected GCMs improve the performance of each individual GCM.

Description: ABSTRACT Aerosol optical depth (AOD) has become one of the most crucial parameters for climate change assessment. This study presents long-term (2002–2016) spatio-temporal distributions and trends in AOD over East Africa (EA) retrieved from the moderate-resolution imaging spectroradiometer (MODIS) Aqua [Dark Target (DT) and Deep Blue (DB)] and multi-angle imaging spectroradiometer (MISR). An inter-comparison of AODs retrieved from different algorithms noticed significant positive correlations ( r  = 0.72 − 0.87) with MISR underestimating MODIS. Moderate (〉0.5–0.8) to high (≥0.8) correlations in AOD exhibited over EA, with a few regions representing low (0–0.5) positive correlations. The spatial patterns of annual mean AOD were generally characterized by low (〈0.2), moderate (0.2–0.35) and high (〉0.35) centres over EA. The seasonal mean AODs over EA were found high (low) during the local dry (wet) seasons, with annual mean (±σ) values of 0.20 ± 0.01, 0.18 ± 0.01 and 0.20 ± 0.02 as observed by DT, DB and MISR, respectively. A single peak distribution of frequencies in AOD was observed by the three sensors in the interval 0.1–0.2, signifying a generally less polluted environment dominated by particular aerosol type. Linear trend analysis revealed an increase in AOD by 0.52, 0.57 and 0.74% year −1 as detected by MISR, DT and DB, respectively, and were consistent with those noted in key meteorological parameters. Furthermore, annual and seasonal spatial trends and tendencies revealed a general increase in AOD over EA, being positive and significant over the northern part of EA. Later, classification of major aerosol types over major cities in EA revealed dominance of continental (74.47%) followed by the mixed (16.22%) and biomass-burning/urban-industrial (8.02%) aerosols, with minor contributions from desert dust (1.03%) and clean maritime (0.32%) type of aerosols. AOD retrieved from MODIS and MISR compared well over East Africa (EA), exhibiting moderate to high correlations. Spatial AOD patterns over EA characterized by low, moderate and high AOD centers. Significant positive trends in AOD were noticed over the northern parts of EA, consistent with those found in key meteorological parameters. Dominant aerosol types revealed varying percentage contribution over EA.

Description: ABSTRACT Southern Peru receives over 60% of its annual climatological precipitation during the short period of January–March. This rainy season precipitation exhibits strong inter-annual and decadal variability, including severe drought events that incur devastating societal impacts and cause agricultural communities and mining facilities to compete for limited water resources. Improving existing seasonal prediction models of summertime precipitation could aid in water resource planning and allocation across this water-limited region. While various underlying mechanisms modulating inter-annual variability have been proposed by past studies, operational forecasts continue to be largely based on rudimentary El Niño-Southern Oscillation (ENSO)-based indices, such as Niño3.4, justifying further exploration of predictive skill. To bridge the gap between understanding precipitation mechanisms and operational forecasts, we perform systematic studies on the predictability and prediction skill of southern Peru's rainy season precipitation by constructing statistical forecast models using best available weather station and reanalysis data sets. We construct a simple regression model, based on the principal component (PC) tendency of tropical Pacific sea surface temperatures (SST), and a more advanced linear inverse model (LIM), based on the empirical orthogonal functions of tropical Pacific SST and large-scale atmospheric variables from reanalysis. Our results indicate that both the PC tendency and LIM models consistently outperform the ENSO-only based regression models in predicting precipitation at both the regional scale and for individual station, with improvements for individual stations ranging from 10 to over 200%. These encouraging results are likely to foster further development of operational precipitation forecasts for southern Peru. In this article, we first re-examined the characteristics of southern Peru precipitation and its relationship with ENSO by using newly collected rain gauge data and reanalysis data sets. Then we reviewed the current forecast skill of existing and potential existed forecasts. At last we introduced two simple statistical models to predict southern Peru precipitation anomalies at both regional and station levels, with both models demonstrating improvement over existing models based on retrospective forecast experiments.

Description: ABSTRACT Pan evaporation ( E pan ) is reported to have exhibited a decreasing trend in many regions of the world over the past several decades. However, recently, the latest studies have discovered the inconsistent phenomenon that the E pan of some regions showed an increasing trend with climate change. E pan is regarded as a critical indicator that plays a significant role in atmospheric evaporative demand, and its trend has an important significant indication to climate change and ecological environment changes. In this article, we adopted the PenPan model and the method of the total short-wave irradiance of the pan to reparameterize the PenPan-20 model for the Qinghai–Tibet Plateau (QTP). In addition, we employed sensitivity and a contribution model to analyse the attribution of changes in E pan under climate change over the QTP in 1970–2011. The results showed that the PenPan model can be applied to QTP. Furthermore, the results showed significant decreasing trends of E pan in 1970–2001 and insignificant increasing trends of E pan in 2002–2011. Therefore, we compartmentalized the two periods to analyse the cause of changing E pan by sensitivity and contribution rate. Trend analysis determined that the combined effects of decreasing net radiation and wind speed contributed to the decreasing of E pan in 1970–2001, and the increasing vapour pressure deficit contributed to the increasing of E pan in the study area in 2002–2011. Meanwhile, sensitivity analysis revealed that net radiation was the most sensitive factor. In addition, the results of analysis of the contribution rate were consistent with trend analysis. The dominant factor of changing E pan varied in different periods via qualitative and quantitative analysis. Distribution of meteorological sites and elevation of the Qinghai–Tibetan Plateau.

Description: The Mars Exploration Rover Opportunity (MER-B) has been exploring the surface of Mars since landing in 2004. Its Alpha Particle X-ray Spectrometer (APXS) is primarily used to interrogate the chemical composition of rocks and soil samples in situ. Additionally, the APXS has measured the atmosphere of Mars with a regular cadence, monitoring the change in relative atmospheric argon density. Atmospheric measurements with the MER-B APXS span over six Mars years providing an unprecedented level of statistics for careful study of the ubiquitous APXS spectral background. Several models were applied to high-frequency long-duration Spirit rover atmospheric APXS measurements. The most-stable model with the least uncertainty was applied to the MER-B data set. Seasonal variation of 10-15% in equatorial atmospheric argon density was observed-in agreement with existing literature and global climate models (GCMs). Unseen in previous work and GCMs, an abrupt deviation from the model-predicted annual mixing ratio was measured by the MER-B APXS around L s 150. The sharp change, ~10% over 10 o L s , provides strong evidence for a northward migrating front, enriched in argon, sourced from the south pole at the end of southern winter. A similar weaker front is possibly observed around L s 325, sourced from the northern polar region.

Description: Basaltic volcanism is one of the most important geologic processes of the Moon. Research on the thickness and volume of late-stage basalts of Mare Imbrium helps better understand the source of lunar volcanism and eruption styles. Based on whether apparent flow fronts exist or not, the late-stage basalts within Mare Imbrium were divided into two groups, namely, Upper Eratosthenian basalts (UEm) and Lower Eratosthenian basalts (LEm). Employing the topographic profile analysis method for UEm and the crater excavation technique for LEm, we studied the thickness and distribution of Eratosthenian basalts in Mare Imbrium. For the UEm units, their thicknesses were estimated to be ~16–34 (±2) m with several layers of individual lava (~8–13 m) inside. The estimated thickness of LEm units was ~14–45(±1) m, with a trend of reducing thickness from north to south. The measured thickness of late-stage basalts around the Chang'E-3 landing site (~37±1 m) was quite close to the results acquired by the lunar penetrating radar carried onboard the Yutu Rover (~35 m). The total volume of the late-stage basalts in Mare Imbrium was calculated to be ~8671 (±320) km 3 , which is four times lower than that of Schaber's estimation (~4 × 10 4 km 3 ). Our results indicate that the actual volume is much lower than previous estimates of the final stage of the late basaltic eruption of Mare Imbrium. Together, the area flux and transport distance of the lava flows gradually decreased with time. These results suggest that late-stage volcanic evolution of the Moon might be revised.

Description: ABSTRACT In the southwest Pacific (SWP) tropical cyclones (TCs) account for 76% of the regions natural disasters and have substantial economic, physical and environmental impacts on people and places. Therefore, information is needed to better understand when and where TCs are likely to occur, as this can aid in preparedness and planning. While there is a well-established relationship between Pacific Ocean sea surface temperature (SST) variability and tropical cyclogenesis (TC genesis) in the SWP, it does not fully explain the historical spatial and temporal variability observed. Therefore, this study aims to look beyond the Pacific and establish a new relationship between Indian Ocean SST variability and SWP TC genesis. This is achieved by statistically relating indices of Indian Ocean SST variability to SWP TC genesis positions. The physical mechanisms driving these observed relationships are then established by studying changes in the environmental conditions conducive to TC genesis. This analysis shows that Indian Ocean SST variability significantly modulates the clustering of SWP TC genesis, where warmer (cooler) SSTs in the eastern and western regions of the Indian Ocean result in a statistically significant north/east (south/west) migration of TC genesis by up to 950 km. Importantly, this relationship is shown to be consistent when the El Niño/Southern Oscillation (ENSO, the dominant Pacific mode) is in an inactive phase (ENSO neutral). Favourable TC genesis parameters including warm SSTs, increased relative humidity, anomalously negative 700 hPa vorticity, anomalously negative and low absolute 200–850 hPa vertical wind shear account for the observed shift in clustering. Furthermore, we show that the combined effect of ENSO/Indian Ocean SST variability results in varying risk profiles for island nations of the region, with the two climate modes either enhancing or suppressing individual impacts. Significantly, the findings from this study provide an opportunity for meteorological agencies to improve seasonal SWP TC outlooks. TC genesis, KDE contours and MCC for positive/negative phases of IOD E, IOD W and II during ENSO neutral conditions (NDJFMA). TC genesis, KDE contours and MCC for ENSO neutral seasons is also included for reference (bold frame).

Description: ABSTRACT The role that the Indonesian Throughflow plays on climate is investigated in an alternative scenario, expected during glacial ages. The equatorwards shift of the Southern Hemisphere westerlies found in glacial ages acts to decrease the Agulhas Leakage (AL) and the thermohaline circulation (THC) in the Atlantic. Recent results suggest that these changes are followed by an increased THC in the Pacific, through an inter-basin seesaw mechanism. The enhanced circulation in the Pacific demands thermocline water to cross the equator towards northern latitudes, which shifts the water source of the throughflow from the low-salinity North Pacific to the relative saltier South Pacific. It is shown that in this equilibrium, the salinity anomalies of the throughflow impact the inter-basin seesaw towards the restoration of the modern climate, enhancing the North Atlantic Deep Water (NADW) formation and decreasing the THC in the Pacific. These results are consistent with paleo-observations and provide new insights to interpreting the climate changes in glacial periods. The present investigation has found that in an alternative climate, where the thermohaline circulation in the Pacific ocean is intensified towards an Atlantic-like circulation, the Indonesian Throughflow acts to restore the circulation as it is known for the modern climate. Furthermore, our results show that many aspects observed in the tropical Pacific in glacial times, inferred from paleo-observations, might be explained by the impacts of the throughflow and its connection with the inter-basin seesaw mechanism.

Description: Recent measurements by the Imaging Ultraviolet Spectrograph (IUVS) instrument on NASA's Mars Atmosphere and Volatile EvolutioN (MAVEN) mission show that a persistent layer of Mg + ions occurs around 90 km in the Martian atmosphere, but that neutral Mg atoms are not detectable. These observations can be satisfactorily modeled with a global ablation rate of 0.06 metric tonnes of magnesium sol -1 , out of a cosmic dust input of 2.7 ± 1.6 t sol -1 . The absence of detectable Mg at 90 km requires that at least 50% of the ablating Mg atoms ionize through hyperthermal collisions with CO 2 molecules. Dissociative recombination of MgO + .(CO 2 ) n cluster ions with electrons to produce MgCO 3 directly, rather than MgO, also avoids a buildup of Mg to detectable levels. The meteoric injection rate of Mg, Fe and other metals – constrained by the IUVS measurements - enables the production rate of metal carbonate molecules (principally MgCO 3 and FeCO 3 ) to be determined. These molecules have very large electric dipole moments (11.6 and 9.2 Debye, respectively), and thus form clusters with up to 6 H 2 O molecules at temperatures below 150 K. These clusters should then coagulate efficiently, building up metal carbonate-rich ice particles which can act as nucleating particles for the formation of CO 2 -ice clouds. Observable mesospheric clouds are predicted to occur between 65 and 80 km at temperatures below 95 K, and above 85 km at temperatures about 5 K colder.

Description: Fatigue can cause materials that undergo cyclic loading to experience brittle failure at much lower stresses than under monotonic loading. We propose that the lithospheres of icy satellites could become fatigued and thus weakened by cyclical tidal stresses. To test this hypothesis, we performed a series of laboratory experiments to measure the fatigue of water ice at temperatures of 198 K and 233 K and at a loading frequency of 1 Hz. We find that ice is not susceptible to fatigue at our experimental conditions and that the brittle failure stress does not decrease with increasing number of loading cycles. Even though fatigue was not observed at our experimental conditions, colder temperatures, lower loading frequencies, and impurities in the ice shells of icy satellites may increase the likelihood of fatigue crack growth. We also explore other mechanisms that may explain the weak behavior of the lithospheres of some icy satellites.

Description: Impact cratering is likely a primary agent of regolith generation on airless bodies. Regolith production via impact cratering has long been a key topic of study since the Apollo era. The evolution of regolith due to impact cratering, however, is not well understood. A better formulation is needed to help quantify the formation mechanism and timescale of regolith evolution. Here, we propose an analytically derived stochastic model that describes the evolution of regolith generated by small, simple craters. We account for ejecta blanketing as well as regolith infilling of the transient crater cavity. Our results show that the regolith infilling plays a key role in producing regolith. Our model demonstrates that, because of the stochastic nature of impact cratering, the regolith thickness varies laterally, which is consistent with earlier work. We apply this analytical model to the regolith evolution at the Apollo 15 site. The regolith thickness is computed considering the observed crater size-frequency distribution of small, simple lunar craters (〈 381 m in radius for ejecta blanketing and 〈 100 m in radius for the regolith infilling). Allowing for some amount of regolith coming from the outside of the area, our result is consistent with an empirical result from the Apollo 15 seismic experiment. Finally, we find that the timescale of regolith growth is longer than that of crater equilibrium, implying that even if crater equilibrium is observed on a cratered surface, it is likely the regolith thickness is still evolving due to additional impact craters.

Description: ABSTRACT The lunar highlands are isostatically compensated at large horizontal scales, but the specific compensation mechanism has been difficult to identify. With topographic data from the Lunar Orbiter Laser Altimeter and gravity data from the Gravity Recovery and Interior Laboratory, we investigate support of highland topography. Poor correlation between crustal density and elevation shows that Pratt compensation is not important in the highlands. Using spectrally weighted admittance, we compared observed values of geoid-to-topography ratio (GTR) with those predicted by isostatic models. Observed GTRs are 25.8 –5.7 +7.5 m/km for the nearside highlands and 39.3 –6.2 +5.7 m/km for the farside highlands. These values are not consistent with flexural compensation of long-wavelength topography or Airy isostasy defined under an assumption of equal mass in crustal columns. Instead, the observed GTR values are consistent with models of Airy compensation in which isostasy is defined under a requirement of equal pressures at equipotential surfaces at depth. The gravity and topography data thus reveal that long-wavelength topography on the Moon is most likely compensated by variations in crustal thickness, implying that highland topography formed early in lunar history before the development of a thick elastic lithosphere.

Description: ABSTRACT The summer rainfall in China in 2016 exhibited a substantial intraseasonal feature, with an intensification in June and July but a suppression in August over the Yangtze River Basin and North China. The Madden–Julian oscillation (MJO) during the summer and its impact on rainfall in China are investigated by conducting observational analyses and diagnostic linear baroclinic model (LBM) experiments. A significant MJO activity in the summer is observed with three MJO episodes corresponding to three stages of rainfall in China. The LBM is utilized to diagnose the circulation response to the tropical heating forcing associated with each MJO episode. The results suggest that much of the atmospheric circulation linked to the anomalous rainfall is attributed to the strong MJO episodes. During June–July (August), the enhanced (suppressed) convection over the tropical Indian Ocean along with the suppressed (enhanced) convection over the South China Sea (SCS) to the western Pacific excite an ‘East Asian–Pacific’ north-eastward-propagating Rossby wave train, inducing anomalous low-level anticyclonic (cyclonic) flows over the northern SCS and the western North Pacific but cyclonic (anticyclonic) flows over North China. They lead to a westward (eastward) shift and strengthening (weakening) of the western Pacific subtropical high, thus favouring the intensification (suppression) in rainfall over the Yangtze River Basin and North China along with the opposite variation over South China. Relative to the first MJO episode, the MJO convection in the second episode causes a northward movement of the anomalous rainfall band from the Yangtze River Basin to North China. Apart from the impact on the above regions, the first (second and third) MJO episode favours an increase (reduction) in rainfall over Northeast China. A significant Madden–Julian oscillation (MJO) activity in the 2016 summer is observed with three MJO episodes corresponding to three stages of rainfall in China. The transition of the rainfall pattern is closely related to the propagation of the MJO. The atmospheric circulation linked to the anomalous rainfall can be modulated by the anomalous MJO convection through exciting a Rossby wave train and thus leading to the variability of the western Pacific subtropical high.

Description: Impact craters on Mars have been extensively modified by ancient geologic processes that may have included rainfall and surface runoff, snow and ice, denudation by lava flows, burial by aeolian material, or others. Many of these processes can leave distinct signatures on the morphometry of the modified impact crater as well as the surrounding landscape. To look for signs of potential regional differences in crater modification processes, we conducted an analysis of different morphometric parameters related to modified impact craters located in the Margaritifer Sinus, Sinus Sabaeus, Iapygia, Mare Tyrrhenum, Aeolis, and Eridania quadrangles, including depth, crater wall slope, crater floor slope, the curvature between the interior wall and the crater floor slope, and the curvature between the interior wall and surrounding landscape. A Welch's t-test analysis comparing these parameters shows that fresh impact craters (Type 4) have consistent morphologies regardless of their geographic location examined in this study, which is not unexpected. Modified impact craters both in the initial (Type 3) and terminal stages (Type 1) of modification also have statistically consistent morphologies. This would suggest that the processes that operated in the late Noachian were globally ubiquitous, and that modified craters eventually reached a stable crater morphology. However, craters preserved in advanced (but not terminal) stages of modification (Type 2) have morphopholgies that vary across the quadrangles. It is possible that these variations reflect spatial differences in the types and intensity of geologic processes that operated during the Noachian, implying that the ancient climate also varied across regions.

Description: No abstract is available for this article.

Description: We report the results of geological studies by the Opportunity Mars rover on the Endeavour Crater rim. Four major units occur in the region (oldest to youngest): the Matijevic, Shoemaker, Grasberg and Burns formations. The Matijevic formation, consisting of fine-grained clastic sediments, is the only pre-Endeavour-impact unit and might be part of the Noachian etched units of Meridiani Planum. The Shoemaker formation is a heterogeneous polymict impact breccia; its lowermost member incorporates material eroded from the underlying Matijevic formation. The Shoemaker formation is a close analog to the Bunte Breccia of the Ries Crater, although the average clast sizes are substantially larger in the latter. The Grasberg formation is a thin, fine-grained, homogeneous sediment unconformably overlying the Shoemaker formation, and likely formed as an airfall deposit of unknown areal extent. The Burns formation sandstone overlies the Grasberg, but compositions of the two units are distinct; there is no evidence that the Grasberg formation is a fine-grained subfacies of the Burns formation. The rocks along the Endeavour Crater rim were affected by at least four episodes of alteration in the Noachian and Early Hesperian: (i) vein formation and alteration of pre-impact Matijevic formation rocks; (ii) low-water/rock alteration along the disconformity between the Matijevic and Shoemaker formations; (iii) alteration of the Shoemaker formation along fracture zones; and (iv) differential mobilization of Fe and Mn, and CaSO 4 -vein formation in the Grasberg and Shoemaker formations. Episodes (ii) and (iii) possibly occurred together, but (i) and (iv) are distinct from either of these.

Description: Using Moon Mineralogy Mapper data, we characterize surface diversity across the enormous South Pole - Aitken Basin (SPA) by evaluating the abundance and composition of pyroxenes, which are overwhelmingly the most abundant mafic mineral in the region. Although SPA exhibits significant complexity due to billions of years of geologic processes subsequent to formation, the basin has retained regular patterns of compositional heterogeneity across its structure. Four distinct, roughly concentric zones are defined: (1) a central SPA compositional anomaly (SPACA), which exhibits a pervasive elevated Ca,Fe-rich pyroxene abundance, (2) a Mg-Pyroxene Annulus, which is dominated by abundant Mg-rich pyroxenes, (3) a Heterogeneous Annulus, which exhibits localized pyroxene-rich areas spatially mixed with feldspathic materials, and (4) the SPA Exterior, which is primarily feldspathic. Pyroxene compositions in the Heterogeneous Annulus are similar to those in the Mg-Pyroxene Annulus, and Mg-rich pyroxenes also underlie the more Ca,Fe-rich pyroxene surface material across SPACA. The establishment of these four distinct compositional zones across SPA constrains future basin evolution models serves to guide potential sample return (and other science) targets.

Description: Post-Noachian Martian paleochannels indicate the existence of liquid water on the surface of Mars after about 3.5 Gya [ Irwin et al. , 2015; Palucis et al. , 2016]. In order to explore the effects of variations in CO 2 partial pressure and obliquity on the possibility of surface water, we created a zero-dimensional surface energy balance model. We combine this model with physically consistent orbital histories to track conditions over the last 3.5 Gyr of Martian history. We find that melting is allowed for atmospheric pressures corresponding to exponential loss rates of or faster, but this rate is within 0.5 σ of the rate calculated from initial measurements made by the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, if we assume all the escaping oxygen measured by MAVEN comes from atmospheric CO 2 [ Lillis et al. , 2017; Tu et al. , 2015]. Melting at this loss rate matches selected key geologic constraints on the formation of Hesperian river networks, assuming optimal melt conditions during the warmest part of each Mars year [ Irwin et al. , 2015; Stopar et al. , 2006; Kite et al. , 2017a,b].. The atmospheric pressure has a larger effect on the surface energy than changes in Mars's mean obliquity. These results show that initial measurements of atmosphere loss by MAVEN are consistent with atmospheric loss being the dominant process that switched Mars from a melt-permitting to a melt-absent climate [ Jakosky et al. , 2017], but non-CO 2 warming will be required if 〈2 Gya paleochannels are confirmed, or if most of the escaping oxygen measured by MAVEN comes from H 2 O.

Description: ABSTRACT India is very prone to heat waves during April–June. The intra-annual variability of heat wave episodes over the east coast of India has been studied using 16-year NCMRWF global forecast system (NGFS) retrospective data. The objective of this study is threefold: (1) identification of heat wave episodes over the east coast of India, (2) intra-annual variability of heat wave episodes, and (3) which physical mechanism(s) is responsible for its occurrence and long-lasting? A total of ten heat wave episodes (100 hot days) were obtained for the period 2000–2015. The intensity of heat wave is found to be maximum (minimum) for 2015 (2007) episode. The average duration of heat wave episodes was 10 days, with the longest episode lasting for 20 days in the year 2003. Moreover, an average duration of severe heat wave is 3.5 days longer than that of a normal heat wave. The common feature observed in all heat wave cases is the presence of anticyclone in the upper troposphere and associated persistence high. This can cause sinking motion, which leads to surface warming due to adiabatic compression. The lack of soil moisture (SM) induces a positive feedback between the surface and the air above it, which amplifies the sensible heating and thereby increases surface temperature. The prevailed westerly anomalies over the study region which reduce the land–sea breeze result in heat wave. The heat wave episodes exhibit a significant intra-annual variability. Intensity of heat waves averaged over the east coast of India has shown an increase of 0.06 °C per heat wave. The geopotential height anomaly, vertical velocity, and SM exhibit significant intra-annual variability between the episodes and become decisive parameters for the maintenance and variability. The correlation coefficient between the maximum temperature and SM is found to be −0.56, indicating the importance of SM regulating the intensity of heat waves. Time-series of area-averaged maximum temperature ( T max ) (top panel), representing the intensity of heat wave, and the corresponding T max anomalies are shown in bars (bottom panel), illustrating the intra-annual variability of heat waves. The dashed black (red) lines represents climatological temperature + 4 (5) °C, respectively.

Description: ABSTRACT Recent and historical austral summer and winter rainfall characteristics have been widely investigated across southern Africa. However, a notable gap of knowledge remains for the Namibian region. This article presents the first extensive 19th century (1845–1900) hydro-climate history for central Namibia, derived from documentary evidence. Unpublished and published data sources were scrutinized in various archives and libraries in Germany, Switzerland, Namibia and South Africa. Missionary Carl Hahn's detailed diaries are the most valuable source of information for the earliest period until 1859. Other important sources of information include the Rhenish Missionary Society (RMS) annual reports and monthly ‘Berichte’ (news), station chronicles, official annual reports for the colonial period (1894 onwards) and letters/diaries by traders, travellers, etc. Climate information was transcribed, translated and organized chronologically. Using a five-point categorization system ranging from very wet (+2) to very dry (−2), each year was classified according to overall rainfall conditions during the rain season. A portion of the chronology is compared with instrumental rainfall data for Okahandja, Windhoek and Rehoboth and confirms good agreement. Possible associations between El Niño-Southern Oscillation (ENSO) phases and subsequent austral summer rainfall conditions are explored for central Namibia. Wetter years (42%) are over-represented in comparison to dry years (38%) during the second half of the 19th century in central Namibia, with a high percentage (42%) constituting either extremely wet or extremely dry years. Inter-annual rainfall variability between 1845 and 1900 seems more pronounced than elsewhere in southern Africa during this period. Extreme to very strong and prolonged El Niño (e.g. 1876–1878) and La Nina (e.g. 1865–1866) phases account for rare hydro-climatic synchronicity between southern African sub-regions and between continents of the Southern Hemisphere. Negligible relative rainfall trend for central Namibia from 1845 to 1900. Very high inter-annual hydro-climatic variability over central Namibia from 1845 to 1900. Extended and very strong to severe ENSO phases produce extreme climatic conditions and rare hydro-climatic synchronicity across southern African summer rainfall sub-regions, and even across continents of the Southern Hemisphere.

Description: ABSTRACT As an important bottom-up driver of ecosystem processes, rainfall is intrinsically linked to the dynamics of vegetation and species distributions through its effects on soil moisture content and surface water availability. Rainfall effects are thus spatially and temporally specific to different environmental role-players. Knowledge of its spatio-temporal pattern is therefore essential to understanding natural ecosystem flux and potential climate change effects. Climate change poses a serious threat to protected areas in particular, as they are often isolated in fragmented landscapes and confined within hard park boundaries. In consequence, a species' natural movement response to resulting climate-induced niche shifts is often obstructed. Long-term, accurate and consistent climate monitoring data are therefore important resources for managers in large protected areas like the Kruger National Park (Kruger). In this article we model local rainfall measurements as a function of global rainfall surfaces, elevation and distance to the ocean using a generalized additive mixed effects model to produce fine-scale (1 km 2 ) monthly rainfall surfaces from July 1981 to June 2015. Results show a clear seasonal cycle nested within an oscillating multi-decadal trend. Most noticeably, seasonality is shifting both temporally and spatially as rainfall moves outside of the typical dry/wet periods and areas. In addition, high-rainfall seasons are generally receiving more rainfall while low-rainfall seasons are receiving less. Northwestern regions of the park are experiencing more extreme annual rainfall differences, while far northern and southern regions show greater seasonality changes. The well-described north–south and east–west rainfall gradient is still visible but the spatial complexity of this pattern is more pronounced than expected. Taken together, we show that Kruger's spatio-temporal rainfall patterns are changing significantly in the short to medium term. The resulting raster data set is made freely available to promote holistic ecosystem studies and support longer-term climate change research ( http://dataknp.sanparks.org/sanparks/ ). Using generalized additive mixed effects models to explore the variability of local rainfall observations as a function of global rainfall surfaces, elevation and distance to the ocean. Results suggest significant change in spatio-temporal patterns of rainfall in the Kruger National Park, South Africa from 1985 to 2015.

Description: ABSTRACT We investigate methodological uncertainties associated with the standardized precipitation index (SPI) that result from limited record length, trends, and outliers. We use long, homogenous records from 14 Italian stations to investigate how specific features in the precipitation record affect construction of an underlying gamma probability function. We apply a resampling scheme to the long records in order to estimate confidence intervals associated with a range of precipitation characteristics. Stability in parameter estimation increases nonlinearly as record length increases. The resulting SPI estimates for 30-year reference periods have considerably more uncertainty than those made from 60-year records. In general, increasing record length beyond 60-years has limited benefits and, in the presence of a trend, may increase uncertainty. Extreme events also have significant influence on SPI estimates, even for records exceeding 60 years. Despite using stations from different geographic regions, each with unique precipitation characteristics, we find consistent confidence interval estimates across stations. These confidence intervals can be applied to specific time series to identify how trends, changes in variability, and outliers during a particular reference period influence SPI values. Estimates of the standardized precipitation index (SPI) have inherent uncertainties associated with limited record length, trends, and outliers. Despite the uniqueness of individual precipitation records, there is consistency in SPI confidence interval estimates across stations and distinct patterns based on record length. Such estimates can be applied to specific time series to identify how trends, changes in variability, and outliers during a particular reference period influence SPI values.

Description: ABSTRACT UK seasonal mean temperature and precipitation conditions are extremely variable from one year to the next but in the last decade have featured several cool, wet summers and mild, wet winters interspersed with some notable cold winter episodes. Jet stream variability is a major determinant of these fluctuations and is often represented by the North Atlantic Oscillation (NAO) index. Recent work has shown some evidence of promising predictability in the winter NAO from 1 to 2 months ahead, while summer predictability remains very limited. Although the phase and magnitude of the NAO influences total UK rainfall, there are regional variations which it does not explain. Here we examine the relationship between UK regional summer and winter precipitation and temperature and a range of North Atlantic atmospheric circulation indices. While the NAO shows a significant relationship with temperature in both seasons and summer rainfall over most of the UK, the picture in winter is more complicated, with other circulation indices such as the East Atlantic pattern explaining rainfall anomalies in southern England. Other indices also show significant relationships with precipitation in regions where the NAO does not. Because UK weather is determined by the interplay between different circulation indices, attention should be given to developing seasonal forecasts of other circulation indices to complement the NAO forecasts. We also find that some potential drivers of jet stream variability are significantly associated with UK temperature and rainfall variability, particularly in summer. This provides further scope for producing seasonal forecasts based directly on these drivers. Improved seasonal forecasts will be useful to a range of end users in agriculture, energy supply, transport and insurance industries and can be extended to other UK weather variables such as extreme rainfall events and storm frequency, and related metrics such as wind power capacity and solar energy. The winter North Atlantic Oscillation is predictable from a few months ahead, but does not explain all regional UK precipitation and temperature anomalies. We examine associations between a number of circulation indices and UK summer and winter temperature and rainfall patterns. The East Atlantic and Scandinavian patterns explain significant regional variations in UK weather, and some drivers of summer jet stream variability are directly associated with summer temperature and precipitation variability. There is potential to develop improved regional seasonal forecasts.

Description: ABSTRACT The North Pacific subtropical front (NPSTF) of sea surface temperature (SST) is an important subtropical feature in the North Pacific. In this study, we reveal that the inter-annual variability of the spring NPSTF has a robust correlation with the El Niño-Southern Oscillation (ENSO) in the following winter over the period of 1961–2016. When there is a strong spring NPSTF, anomalous cyclonic and anticyclonic circulations in the low troposphere occur to its north and south, respectively. The northeasterly wind anomaly associated with the anticyclonic circulation increases the climatological northeasterly wind over the subtropical Northeast Pacific, resulting in SST decrease via the wind–evaporation–SST feedback. The SST and wind perturbations propagate southwards from the subtropical to the eastern central equatorial Pacific in summer and grow via the Bjerknes feedback from summer to winter, eventually leading to a La Niña event in winter. A strong spring NPSTF induces an anomalous anticyclonic circulation to its south through both transient eddy activity and atmospheric heat source anomaly. The enhanced air temperature gradient due to a strong NPSTF increases the atmospheric baroclinicity, favouring an enhanced transient eddy activity over the NPSTF and to the north. The enhanced transient eddy activity triggers a significant negative height anomaly to the north via high-frequency transient eddy feedback forcing, which is conductive to an anticyclonic circulation over the subtropical North Pacific through the downstream effect of Rossby waves. On the other hand, the convergence and increased atmospheric baroclinicity related to the strong NPSTF act to enhance precipitation over the NPSTF and to the north, corresponding to the increased atmospheric heat source, which can also excite an anomalous anticyclonic circulation over the subtropical North Pacific. The spring NPSTF is negatively correlated with the ENSO in the following winter. Anticyclonic circulation due to a strong NPSTF in spring generates negative SST anomalies over the subtropical Northeast Pacific, which grow via the WES and Bjerknes feedback to a La Nina event in winter. Both transient eddy activity and atmospheric heat source play roles in the NPSTF inducing the anticyclonic circulation in spring.

Description: ABSTRACT This study provides an assessment of recent changes in near-surface air temperature over the central Adriatic region of Italy, focusing on extreme events at annual and seasonal scales. It investigates trends in selected indices calculated from quality controlled and homogenized daily temperature data recorded from 1980 to 2012 at 34 meteorological stations distributed over the territory. The results reveal overall warming tendencies, particularly pronounced in spring and summer, with significant increases in the duration of warm spells (WSDI) and in the frequency of warm days (TX90p) and warm nights (TN90p), summer days (SU) and tropical nights (TR). Moreover, cold-related extremes (cold spell duration (CSDI), cool days (TX10p) and cool nights (TN10p), frost days (FD) and icing days (ID)) show significant reductions, although of lower magnitudes, thus confirming the recent warming over the study domain. Prevalent increasing tendencies are also observed for absolute extreme temperature indices (highest and lowest daily values of maximum and minimum temperatures), but with more mixed and less uniform spatial patterns. Finally, the influence of large-scale circulation modes on temperature extremes is examined. The results highlight the presence of significant correlations between most of the selected extreme temperature indices and the East-Atlantic pattern, in particular for the warm season. This study examines trends in extreme temperature indices in the central Adriatic region of Italy for the period 1980–2012. The results show overall warming tendencies, particularly pronounced in spring and summer, with significant increases (reductions) in hot (cold) extremes. This study also investigates the influence of large-scale circulation patterns on extreme temperature variability and the results reveal that the registered recent warming is significantly correlated with the East Atlantic pattern.

Description: Thermal tides in the Venus atmosphere are investigated by using a GCM named as AFES-Venus. The three-dimensional structures of wind and temperature associated with the thermal tides obtained in our model are fully examined and compared with observations. The result shows that the wind and temperature distributions of the thermal tides depend complexly on latitude and altitude in the cloud layer, mainly because they consist of vertically propagating and trapped modes with zonal wavenumbers of 1–4, each of which predominates in different latitudes and altitudes under the influence of mid- and high-latitude jets. A strong circulation between the subsolar and antisolar (SS-AS) points, which is equivalent to a diurnal component of the thermal tides, is superposed on the superrotation. The vertical velocity of SS-AS circulation is about 10 times larger than that of the zonal-mean meridional circulation (ZMMC) in 60–70 km altitudes. It is suggested that the SS-AS circulation could contribute to the material transport, and its upward motion might be related to the UV dark region observed in the subsolar and early afternoon regions in low-latitudes. The terdiurnal and quaterdiurnal tides, which may be excited by the nonlinear interactions among the diurnal and semidiurnal tides in mid- and high-latitudes, are detected in the solar-fixed Y-shape structure formed in the vertical wind field in the upper cloud layer. The ZMMC is weak and has a complex structure in the cloud layer; the Hadley circulation is confined to latitudes equatorward of 30 ∘ , and the Ferrel-like one appears in mid- and high-latitudes.

Description: One of the most intriguing, long-standing questions regarding Venus' atmosphere is the origin and distribution of the unknown UV-absorber, responsible for the absorption band detected at the near-UV and blue range of Venus' spectrum. In this work, we use data collected by MASCS spectrograph on board the MESSENGER mission during its second Venus flyby in June 2007 to address this issue. Spectra range from 0.3 μ m to 1.5 μ m including some gaseous H 2 O and CO 2 bands, as well as part of the SO 2 absorption band and the core of the UV absorption. We used the NEMESIS radiative transfer code and retrieval suite to investigate the vertical distribution of particles in the Equatorial atmosphere and to retrieve the imaginary refractive indices of the UV-absorber, assumed to be well mixed with Venus' small mode-1 particles. The results show an homogeneous Equatorial atmosphere, with cloud tops (height for unity optical depth) at 75±2 km above surface. The UV absorption is found to be centered at 0.34±0.03  μ m with a full width half maximum of 0.14±0.01 μ m. Our values are compared with previous candidates for the UV aerosol absorber, among which disulfur oxide (S 2 O) and dioxide disulfur (S 2 O 2 ) provide the best agreement with our results.

Description: The localized loss of near-surface excess ice on Mars by sublimation (and perhaps melting) can produce thermokarstic collapse features such as expanded craters and scalloped depressions, which can be indicators of the preservation of shallow ice. We demonstrate this by identifying HiRISE images containing expanded craters south of Arcadia Planitia (25–40°N), and observe a spatial correlation between regions with thermokarst and the lowest-latitude ice-exposing impact craters identified to date. In addition to widespread thermokarst north of ~35°N, we observe localized thermokarst features that we interpret as patchy ice as far south as 25°N. Few ice-exposing craters have been identified in the southern hemisphere of Mars since they are easier to find in dusty, high-albedo regions, but the relationship among expanded craters, ice-exposing impacts, and the predicted ice table boundary in Arcadia Planitia allows us to extend this thermokarst survey into the southern mid-latitudes (30–60°S) to infer the presence of ice today. Our observations suggest that the southern hemisphere excess ice boundary lies at ~45°S regionally. At lower latitudes, some isolated terrains (e.g., crater fill, pole-facing slopes) also contain thermokarst, suggesting local ice preservation. We look for spatial relationships between our results and surface properties (e.g., slope, neutron spectrometer water ice concentration) and ice table models to understand the observed ice distribution. Our results show trends with thermal inertia and dust cover, and are broadly consistent with ice deposition during a period with a higher relative humidity than today. Shallow, lower-latitude ice deposits are of interest for future exploration.

Description: Isolated landscapes largely shaped by aeolian processes can occur on Earth, while the majority of Mars’ recent history has been dominated by wind-driven activity. Resultantly, Martian landscapes often exhibit large-scale aeolian features, including yardang landforms carved from sedimentary-layered deposits. High-resolution orbital monitoring has revealed that persistent bedform activity is occurring with dune and ripple migration implying ongoing abrasion of the surface. However, little is known about the interaction between dunes and the topography surrounding them. Here we explore dune-yardang interactions in Becquerel crater in an effort to better understand local landscape evolution. Dunes there occur on the north and south sides of a 700-m-tall sedimentary deposit, which displays numerous superposed yardangs. Dune and yardang orientations are congruent suggesting they both were formed under a predominantly northerly wind regime. Migration rates and sediment fluxes decrease as dunes approach the deposit and begin to increase again downwind of the deposit where the effect of topographic sheltering decreases. Estimated sand abrasion rates (16-40 μm yr -1 ) would yield a formation time of 1.8-4.5 million years for the 70-m-deep yardangs. This evidence for local aeolian abrasion also helps explain the young exposure ages of deposit surfaces, as estimated by the crater size-frequency distribution. Comparisons to terrestrial dune activity and yardang development begin to place constraints on yardang formation times for both Earth and Mars. These results provide insight into the complexities of sediment transport on uneven terrain and are compelling examples of contemporary aeolian-driven landscape evolution on Mars.

Description: Boulder halos are circular arrangements of clasts present at martian middle to high latitudes. Boulder halos are thought to result from impacts into a boulder-poor surficial unit that is rich in ground-ice and/or sediments and that is underlain by a competent substrate. In this model, boulders are excavated by impacts and remain at the surface as the crater degrades. To determine the distribution of boulder halos and to evaluate mechanisms for their formation, we searched for boulder halos over 4,188 HiRISE images located between ~50-80° north and 50-80° south latitude. We evaluate geological and climatological parameters at halo sites. Boulder halos are about three times more common in the northern hemisphere than in the southern (19% vs. 6% of images), and have size-frequency distributions suggesting recent Amazonian formation (tens to hundreds of millions of years). In the north, boulder halo sites are characterized by abundant shallow subsurface ice and high thermal inertia. Spatial patterns of halo distribution indicate that excavation of boulders from beneath non-boulder-bearing substrates is necessary for the formation of boulder halos, but that alone is not sufficient. Rather, surface processes either promote boulder halo preservation in the north or destroy boulder halos in the south. Notably, boulder halos predate the most recent period of near-surface ice emplacement on Mars and persist at the surface atop mobile regolith. The lifetime of observed boulders at the martian surface is greater than the lifetime of the craters that excavated them. Finally, larger minimum boulder halo sizes in the north indicate thicker icy soil layers on average throughout climate variations driven by spin/orbit changes during the last 10s to 100s Ma.

Description: Thermal infrared spectra acquired by Cassini/CIRS in limb viewing geometry in 2015 are used to derive 2-D latitude-pressure temperature and thermal wind maps. These maps are used to study the vertical structure and evolution of Saturn's equatorial oscillation (SEO), a dynamical phenomenon presenting similarities with the Earth's Quasi-Biennal Oscillation (QBO) and Semi-Annual Oscillation (SAO). We report that a new local wind maximum has appeared in 2015 in the upper stratosphere, and derive the descent rates of other wind extrema through time. The phase of the oscillation observed in 2015, as compared to 2005 and 2010, remains consistent with a ∼15-year period. The SEO does not propagate downward at a regular rate, but exhibits faster descent rate in the upper stratosphere, combined with a greater vertical wind shear, compared to the lower stratosphere. Within the framework of a QBO-type oscillation, we estimate the absorbed wave momentum flux in the stratosphere to be on the order of ∼7 × 10 −6 N m −2 . On Earth, interactions between vertically propagating waves (both planetary and mesoscale) and the mean zonal flow drive the QBO and SAO. To broaden our knowledge on waves potentially driving Saturn's equatorial oscillation, we searched for thermal signatures of planetary waves in the tropical stratosphere using CIRS nadir spectra. Temperature anomalies of amplitude 1-4 K and zonal wavenumbers 1 to 9 are frequently observed and an equatorial Rossby (n=1) wave of zonal wavenumber 3 is tentatively identified in November, 2009.

Description: Signatures of lithospheric flexure were previously identified at a dozen or more large coronae on Venus. Thin plate models fit to topographic profiles return elastic parameters, allowing derivation of mechanical thickness and surface heat flows given an assumed yield strength envelope. However, the low resolution of altimetry data from the NASA Magellan mission has hindered studying the vast majority of coronae, particularly those less than a few hundred kilometers in diameter. Here we search for flexural signatures around 99 coronae over ∼20% of the surface in Magellan altimetry data and stereo-derived topography that was recently assembled from synthetic aperture radar images. We derive elastic thicknesses of ∼2 to 30 km (mostly ∼5 to 15 km) with Cartesian and axisymmetric models at 19 coronae. We discuss the implications of low values that were also noted in earlier gravity studies. Most mechanical thicknesses are estimated as 〈19 km, corresponding to thermal gradients 〉24 K km −1 . Implied surface heat flows 〉95 mW m −2 —twice the global average in many thermal evolution models—imply that coronae are major contributors to the total heat budget or Venus is cooling faster than expected. Binomial statistics show that “Type 2" coronae with incomplete fracture annuli are significantly less likely to host flexural signatures than “Type 1" coronae with largely complete annuli. Stress calculations predict extensional faulting where nearly all profiles intersect concentric fractures. We failed to identify systematic variations in flexural parameters based on type, geologic setting, or morphologic class. Obtaining quality, high-resolution topography from a planet-wide survey is vital to verifying our conclusions.

Description: ABSTRACT This study analysed the characteristics of climate change (including temporal trend and spatial distribution of temperature and precipitation) in Yunnan Province, China during 1961–2011 based on the observed data from 22 meteorological stations, and its relationship with land use/cover change (LUCC) was also discussed. The results showed that: (1) Significant increasing trend in temperature was observed at the annual scale, especially for the period 1987–2011. At the seasonal scale, such trend was the most prominent in winter. (2) Temporally, the annual precipitation showed a non-significant decreasing trend, which was dominant by the rainy season; spatially, the annual precipitation showed the east-to-west and north-to-south increasing trends over this region. (3) This study analysed the impacts of elevation and geographical location on climate change patterns, and the statistical equations to estimate the annual temperature and precipitation as well as their changing rates were established based on longitude, latitude and elevation. (4) Through analysing the relationship between climate change and the LUCC, the correlation between the LUCC and temperature was stronger than that between the LUCC and precipitation. The results would be valuable for researchers and managers to better understand the characteristics of climate change as well as its relationship with the LUCC and to make better decisions in future. This article analysed the characteristics of climate change (including temporal trend and spatial distribution of temperature and precipitation) in Yunnan Province, China, for the period 1961–2011. This article investigated the impacts of elevation and geographical location on climate change, and the statistical equations to estimate the annual temperature and precipitation as well as their changing rates were established based on longitude, latitude and elevation. This article preliminarily presented the possible impacts of urbanization through analysing the relationship between climate change and land use/cover change.

Description: ABSTRACT Despite an increasing body of evidence from observed data that climate change is having a significant impact on different types of biogeophysical systems in the Midwest and Great Lakes region, there still remain critical questions of how quickly and how much climate will be altered over this region in the future. For this evaluation, we make use of 31 global climate model (GCM) projections from the Coupled Model Intercomparison Project, Phase 5 (CMIP5). Based on changes in temperature ( T ) and precipitation ( P ) over the Midwest, we selected ten GCM scenarios which (1) simulate historical climate well and (2) successfully capture the range of future climate from the entire CMIP5 ensemble. We then downscaled T and P projections to 1/16° gridded data sets for two different emission scenarios (RCP4.5 and RCP8.5) for three 30-year future periods using the Hybrid Delta (HD) statistical downscaling approach which was proven to be applicable for daily-scale application by a validation work using historical data. T is projected to increase across all seasons, with ensemble mean changes up to 6.5 °C by 2100 for the RCP8.5 scenarios. P increases up to 30% in spring and winter with decreasing snowfall to precipitation ratio, while summer P decreases moderately (−15%) by the 2080s. Changes in daily extreme events show similar seasonal patterns including increasing daily extreme P events in winter and decreasing P in summer. Growing season P may actually increase, however, despite projected P reductions in the warmest summer months. Regional warming results in decreased heating degree days (−1639 °C days, −32%) and increasing cooling degree days (+318 °C days, +957%) by 2080s, with overall net reductions in energy demand. Despite an increasing body of evidence that climate change is having a significant impact on different types of biogeophysical systems in the Midwest and Great Lakes region, there still remain critical questions of how quickly and how much climate will be altered over this region in the future. This study provides future daily temperature and precipitation at high resolution (1/16°) which can be used in many regional impact assessments, and also analyses the projected mean and extreme climate events.

Description: No abstract is available for this article.

Description: ABSTRACT Large-scale patterns of ocean surface temperature can influence weather across the globe and understanding their interaction with the local climate can improve seasonal forecasting of local temperature and precipitation. Here we focus on the combined interactions of the El Niño-Southern Oscillation (ENSO), the Atlantic Multidecadal Oscillation (AMO) and the Pacific Decadal Oscillation (PDO) in the Alabama–Coosa–Tallapoosa (ACT) and Apalachicola–Chattahoochee–Flint (ACF) river basins of the southeastern United States. Nonparametric ranks-sum tests of individual and coupled impacts of these teleconnections on the annual study area climate (1895–2009) found significant impacts. A positive AMO phase was associated with decreased precipitation and increased mean temperature while the negative AMO phase was associated with increased precipitation and decreased temperature. While an El Niño event generally increases regional precipitation, El Niño during a positive AMO or PDO phase resulted in precipitation below the long-term average in our study area. Because of many instances of El Niño being shared between AMO and PDO phase, the effects of the PDO and AMO on El Niño could not be distinguished. La Niña was associated with negative precipitation and increased temperature. The effects of La Niña on the temperature and precipitation anomaly were significantly increased during positive AMO and PDO phases. The coupled impacts of the aforementioned teleconnections demonstrate the necessity of including the effects of the AMO and the PDO when using ENSO-based forecasts. The significant shifts on the effects of teleconnections on area climate from AMO negative phase to AMO positive phase cast doubt on seasonal prediction for the study area based on the recent history (i.e. the use of the period 1950–2000 to predict seasonal climate since 2000). While an El Niño event generally increases regional precipitation, El Niño during a positive AMO or PDO phase resulted in precipitation below the long-term average in our study area. Because of many instances of El Niño being shared between AMO and PDO phase, the effects of the PDO and AMO on El Niño could not be distinguished. The effects of La Niña on the temperature and precipitation anomaly were significantly increased during a positive AMO and PDO phases.

Description: ABSTRACT We review recent climate changes over the Tibetan Plateau (TP) and associated responses of cryospheric, biospheric, and hydrological variables. We focused on surface air temperature, precipitation, seasonal snow cover, mountain glaciers, permafrost, freshwater ice cover, lakes, streamflow, and biological system changes. TP is getting warmer and wetter, and air temperature has increased significantly, particularly since the 1980s. Most significant warming trends have occurred in the northern TP. Slight increases in precipitation have occurred over the entire TP with clear spatial variability. Intensification of surface air temperature is associated with variation in precipitation and decreases in snow cover depth, spatial extent, and persistence. Rising surface temperatures have caused recession of glaciers, permafrost thawing, and thickening of the active layers over the permafrost. Changing temperatures, precipitation, and other climate system components have also affected the TP biological system. In addition, elevation-dependent changes in air temperature, wind speed, and summer precipitation have occurred in the TP and its surroundings in the past three decades. Before projecting multifaceted interactions and process responses to future climate change, further quantitative analysis and understanding of the change mechanisms is required. Responses of hydrosphere, cryosphere, and biosphere to changing climatic system on the TP. SOS means the start of vegetation growing season and EOS represents end of vegetation growing season.

Description: ABSTRACT The main objective of this study was to project changes in the evolution of drought characteristics (frequency, duration and magnitude) during the 21st century in lowlands, highlands and mountainous regions in the Czech Republic (CR). We focused on the multi-scalar nature of droughts as a function of the variables that govern the balance of moisture during climate change, such as precipitation, which supplies moisture, and temperature, which modulates evapotranspiration. Thereby, this issue is addressed with two drought indices, i.e. the standardized precipitation evapotranspiration index (SPEI) and the standardized precipitation index (SPI), for various lags (1, 3, 6, 12 and 24 months). To assess the impact of climate change on drought characteristics, a set of eight regional climate models (RCMs) simulations were selected for further analysis driven by five different global circulation models (GCMs) carried out in the frame of Euro-CORDEX. Future drought changes were developed for the two representative concentration scenarios (RCP4.5 and RCP8.5). For the temporal evolution of the droughts, the monthly drought indices were calculated over the entire study period from 1961 to 2100. The SPEI showed a higher frequency in the categories of severe droughts and extreme droughts than the SPI, while the SPEI yielded fewer events in the extreme wet categories. The probability distribution of the SPEI-6 under the RCP8.5 scenario shifted more than one and a half standard deviations in lowlands at the end of the century, peaking at −1.65 (with a probability of 10.5%). This meant that severe droughts, according to the current climate criteria, will become the new norm in the period 2071–2100. Outlook of the temporal evolution of the SPEI and SPI at a 12-month lag for observed (1961–2015) and the projected historical (1970–2005) and future (2006–2100) drought and wetness events under the pathway scenarios for RCMs of the Euro-CORDEX runs in the lowland region. Outlook of the drought frequency (%) per region at 6-month lag (SPEI/SPI) for historical (1961–2005 or 1970–2005: Hist) and future (2006–2100: Fut) simulations for eight RCMs of the Euro-CORDEX runs under the RCP8.5 scenario. Box plots–central line: median; box: interquartile range (IQR); whiskers: outlier limits (1.5 × the IQR). Region I is characterized by the warmest climate in the country, the highest potential evapotranspiration during the growing season and the most intensive agriculture (lowlands). Region II is characterized by a moderate-temperature regime and less intensive agriculture (highlands). Region III is mostly forested and is characterized by limited agricultural production (mountainous).

Description: ABSTRACT The fragile ecosystem, scarce water resources, and limited ecosystem resilience of Xinjiang, China make the region especially vulnerable to climate change. Researchers need reliable analyses of climate change trends to formulate regional mitigation and adaption strategies and to support sustainable development. Therefore, two statistical downscaling methods and the combination of a Mann–Kendall test with Co-Kriging interpolation were used to investigate the spatiotemporal characteristics of climate change in Xinjiang based on the ensemble of 37 general circulation models (GCMs) in 2021–2060. The reliabilities of single run and ensemble downscaling results of GCMs were evaluated by 69 meteorological stations over the period 1965–2004. The correlation coefficients (CC) with the observations for precipitation and temperature ranged between 0.4–0.8 and 0.9–0.99 in the reference period, respectively. CC improved to 0.87 and was close to 1 after downscaling for precipitation and temperature, respectively. A pronounced increase of ca . 0.27–0.51 °C decade −1 was projected overall, and especially for Representative Concentration Pathway (RCP) 8.5 in northern Xinjiang. In general, the precipitation changed by −1.66 to 6.83% decade −1 while varying seasonally and spatially; a declining tendency emerged in the western regions of Xinjiang during summer. More extreme rainfall events are predicted to occur in summer and autumn months, while warmer extremes would be concentrated in August. The climate in Xinjiang will continue to become warmer and wetter. Nevertheless, Western Xinjiang will experience a warmer and drier climate in summer and autumn. These projections of climate change in the near future are able to provide useful information for the development of potential mitigation measures and adaptation strategies. Multiple circulation mechanisms are also suggested accounting for the changes in precipitation and temperature which will benefit the understanding of the possible drivers of climate variability in this region. The location of Xinjiang Uygur Autonomous Region and meteorological stations used in this study. An inset map shows the location of Xinjiang within China.

Description: ABSTRACT Understanding the spatio-temporal variability of rainfall over mountainous regions such as the Andes is crucial for the maintenance of water resources and ecosystems. This study provided a comprehensive analysis of the signal, statistical significance and spatial pattern of rainfall trends in central and southern Peruvian Andes (CSPA) from 1965 to 2010. Rainfall from 47 quality-controlled rain gauge stations was examined using the hydrologic calendar year. Total and extreme rainfall indices proposed by the Expert Team on Climate Change Detection and Indices (ETCCDI) were calculated and trends were examined with Mann–Kendall test and Sen's slope estimator. Significant regional patterns of changes in rainfall extremes were investigated and compared with previous studies. Four major regions of stations were identified based on principal component analysis and clustering techniques: Amazon, central Pacific, southern Pacific and Titicaca basins. Statistically significant trend patterns showed that the annual total rainfall has decreased in the Amazon basin, despite the increase in the number of rainy days and some extreme rainfall indices. Decrease in 1-day and 5-day yearly maximum rainfall was observed in central Pacific, along with an increase in the number of wet days. Positive trends in indices related to the intensity of very strong daily rainfall were detected in southern Pacific. Titicaca basin showed an increase in the intensity of rainfall extremes. Rainfall variability and trends were evaluated during contrasting El Niño-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO). Most stations in the CSPA exhibited positive (negative) anomaly of total and extreme rainfall indices (consecutive dry days) during La Niña (El Niño) years. Positive (negative) anomalies of annual total rainfall and consecutive dry days during positive (negative) PDO occurred in the Amazon, southern Pacific and Titicaca basins, respectively. The ENSO–PDO conditions may have influenced the complex and mostly non-statistically significant long-term trends in CSPA. Trends in total and extreme rainfall indices over central and southern Peruvian Andes during 1965–2009 water years: (a) wet days annual rainfall (PRCPTOT), (b) consecutive dry days (CDD), (c) very wet day rainfall (R95p) and (d) percentage of wet days (Wdays).

Description: ABSTRACT Errors are quite large in the simulated carbon and water fluxes obtained by global models used for the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, and reducing those errors is important for improving our confidence about these models and their projections. Errors in model parameter values are a major cause of those large modelling errors but can be significantly reduced if model parameter values are optimized. While parameter optimizations have been carried out at local sites or regional scales, parameter optimizations have been rarely conducted at the global scale because of the high computing costs required to optimize a large (〉100) number of model parameters. In this study, we used an adaptive surrogate modelling based optimization (ASMO) method to maximize the match between simulated monthly global gross primary production (GPP) and latent heat flux (LE) derived by two global land surface models (LSMs) and the model-data products for global GPP and LE from the 1982–2008 period generated by the Max Plank Institute. The ASMO method only required a few hundred model runs to find the optimal values of all optimized parameters for the two global LSMs [the Australian Community Atmosphere-Biosphere-Land Exchange (CABLE) and joint UK land environment simulator (JULES)]. Our results show that up to 65% of the model errors can be reduced by parameter optimization for most of the plant functional types (PFTs) and that the model performances of CABLE and JULES are significantly improved at 72 and 93% of the land points, respectively. At last, we discuss the limitations of this work and recommend that parameter optimization based on surrogate modelling using various observational data sets and acceptable prior information of uncertainties in model structure and observations should be considered as a key step in improving the performance of global LSMs or model intercomparisons. Automatic parameter optimization of global land surface models for global gross primary production and latent heat flux can be achieved with 〈700 model runs. Parameter optimization can significantly improve carbon and water cycle simulation at land point, PFT (as shown in the image), and global scales. Parameter optimization using various observational data sets is recommended as a key step in improving land model performance.

Description: ABSTRACT Previous studies documented that El Niño (EN) events are in general associated with negative phases of the Southern Annular Mode (SAM). EN 2015–2016 (EN15–16) was one of the three strongest events ever recorded. However, it was associated with a SAM positive phase of extreme intensity. Furthermore, while the negative linear relationship between ENSO and SAM during the most recent period (1986–2014) was significant and associated with a narrow uncertainty band, the combined condition of both climate patterns in the EN15–16 event was an outlier. The EN15–16 influence on the austral summer circulation anomalies at the extratropical and polar regions of the Southern Hemisphere was considerably altered by the strong SAM positive phase, which was evident not only at the troposphere but also at the stratosphere. Such circulation changes resulted in unusual regional impacts, such as negative anomalies of surface air temperature in western Antarctic Peninsula and negative precipitation anomalies in southeastern South America, ever recorded for previous strong EN events. Further research is needed to better understand the mechanisms explaining the SAM behaviour during 2015–2016 and its implication for climate predictability on seasonal timescales. Previous studies documented that El Niño (EN) events are in general associated with negative phases of the Southern Annular Mode (SAM). EN 2015–-2016 (EN15–-16) was one of the three strongest events ever recorded. However, it was associated with a SAM positive phase of extreme intensity. That combination of climate patterns altered the response of the extratropical circulation in the Southern Hemisphere (SH) typically expected in strong EN. Therefore, the purpose of this work is to analyse the main characteristics of the SAM activity between 2015 and 2016, and its role in modulating the EN15–-16 influence on the climate anomalies in the SH. Boxplots of the detrended SAM values associated with the Historical EN events (blue) and 7 strongest EN events (red) for ASO, SON, OND, NDJ, DJF, and JFM. Crosses indicate the SAM values for the seasons of 2015–-2016.

Description: ABSTRACT We analyse recent trends and variability of observed near-surface wind speed from 19 stations across Saudi Arabia (SA) for 1978–2013. The raw wind speed data set was subject to a robust homogenization protocol, and the stations were then classified under three categories: (1) coast, (2) inland and (3) mountain stations. The results reveal a statistically significant ( p  〈 0.05) reduction of wind speed of −0.058 m s −1 dec −1 at annual scale across SA, with decreases in winter (−0.100 m s −1 dec −1 ) and spring (−0.066 m s −1 dec −1 ) also detected, being non-significant in summer and autumn. The coast, inland and mountain series showed similar magnitude and significance of the declining trends across all SA series, except for summer when a decoupled variability and opposite trends of wind speed between the coast and inland series (significant declines: −0.101 m s −1 dec −1 and −0.065 m s −1 dec −1 , respectively) and the high-elevation mountain series (significant increase: +0.041 m s −1 dec −1 ) were observed. Even though wind speed declines dominated across much of the country throughout the year, only a small number of stations showed statistically significant negative trends in summer and autumn. Most interestingly, a break in the stilling was observed in the last 12-year (2002–2013) period (+0.057 m s −1 dec −1 ; not significant) compared to the significant slowdown detected in the previous 24-year (1978–2001) period (−0.089 m s −1 dec −1 ). This break in the slowdown of winds, even followed by a non-significant recovery trend, occurred in all seasons (and months) except for some winter months. Atmospheric circulation plays a key role in explaining the variability of winds, with the North Atlantic Oscillation positively affecting the annual wind speed, the Southern Oscillation displaying a significant negative relationship with winds in winter, spring and autumn, and the Eastern Atlantic negatively modulating winds in summer. Wind speed declined significantly across Saudi Arabia for 1978–2013. A recent break in the stilling has been detected for 2002–2013. Atmospheric circulation modes partly explain the variability of surface winds.

Description: ABSTRACT In this study, potential impacts of the North Pacific subarctic frontal zone (SAFZ) variation, including its intensity variation and meridional shift, upon the subseasonally varying North Pacific storm track are investigated by using the 100-year reanalysis data sets. Regression analysis indicates that the changes in the SAFZ intensity and meridional position have significant influence on the North Pacific storm track, which intensifies with the strengthening of the SAFZ and moves northwards following the northwards shift of the SAFZ. However, the storm-track response pattern exhibits distinct differences from one calendar month to another. Specifically, the storm-track response to the SAFZ intensity variation is strongest in February and March; while its response to the SAFZ meridional shift is most pronounced in November and December. However, the storm-track response is relatively weak in January. Further analysis shows that the intensified (or northwards shifted) SAFZ would result in changes in the near-surface baroclinicity and hence affects the storm track, while the weak storm-track response in January is not the result of the anomalous near-surface baroclinicity. The investigation of the local energetics reveals that changes in the baroclinic energy conversion (BCEC) associated with the SAFZ variation are consistent with the storm-track anomalies, indicating that the BCEC plays a crucial role in modulating the subseasonal changes in the storm-track response. In January, the weakened BCEC contributes to the reduced storm-track response to the SAFZ variation. This study revealed that the storm track intensifies with the strengthening of the subarctic frontal zone (SAFZ) and moves northwards following the northwards shift of the SAFZ as shown in the figure. The storm-track response to the SAFZ intensity variation is strongest in February and March, while its response to the SAFZ meridional shift is most pronounced in November and December. The storm-track response is relatively weak in January.

Description: ABSTRACT Soil moisture affects hydro-climate processes by altering water and energy exchanges between land surface and atmosphere. Understanding of the predictability of soil moisture is not only important for a skillful forecasting of seasonal hydro-climate, but also for agricultural drought early warning. This paper assesses seasonal forecast skill and potential predictability of soil moisture directly produced by climate models, and investigates an optimal combination of different models over China. A set of 29-year hindcasts for soil moisture from six North American Multi-model Ensemble (NMME) models are verified against ERA Interim reanalysis. Results show that soil moisture predictability, which is defined by anomaly correlation under a perfect model assumption, is higher than forecast skill in all models, suggesting that soil moisture prediction may have a room for improvement. Except the CESM model, NMME climate forecast models with higher predictability also have higher forecast skill, where predictability is positively correlated with forecast skill with p 〈 0.01 across different lead times. Soil moisture forecast skill from NMME simple arithmetic mean is higher than any individual models, and the skill is further improved through an optimization of model weights with a cross validation procedure. As compared with simple ensemble mean, the optimized superensemble mean reduces root mean squared error by 19 and 7% for seasonal mean soil moisture forecast during winter and summer seasons, respectively, and increases correlation by about 10%. This study suggests that soil moisture forecasts directly produced by climate models, when combined appropriately, can provide useful information for climate service. Seasonal mean soil moisture predictability ( x -axis) versus forecast skill ( y -axis) in terms of anomaly correlation at different lead time. Different colors represent different models. All statistics are calculated by using NMME hindcasts during 1982–2010.

Description: ABSTRACT Regional climate models (RCMs) from the North American Regional Climate Change Assessment Program (NARCCAP) are compared with the two gridded precipitation data sets [Climate Prediction Center (CPC) and the University of Washington (UW)] and the North American regional reanalysis (NARR) to examine if RCMs are able to reproduce very heavy precipitation under similar physical conditions seen in observations. The analysis focuses on contemporary climate (1982–1999) in an upper Mississippi region during the summer (June–July–August) months and utilizes output from NARCCAP RCMs forced with a reanalysis and atmosphere–ocean global climate models (AOGCMs). The NARCCAP models generally reproduce the precipitation frequency versus intensity spectrum seen in observations up to around 25 mm day −1 , before producing overly strong precipitation at high intensities. CRCM simulations produce lower precipitation amounts than the rest of the models and observations past the 25 mm day −1 threshold. Further analysis focuses on precipitation events exceeding the 99.5th percentile that occur simultaneously at several points in the region, yielding ‘widespread events’. Apart from the CRCM and EPC2 simulations, models and observations produce peaks in widespread events during 0300–0900 UTC, although the models typically produce slightly weaker intensities compared to observations. Widespread precipitation falls too frequently throughout the day, especially between 1500 and 2100 UTC, compared to observations. Composite precipitation shows inter-model differences in magnitude and location of widespread events. Examination of additional fields shows that NARCCAP models produce credible representations of very heavy precipitation and their supporting environments when compared to the NARR. Composite daily precipitation during widespread very heavy events for observations and RCM simulations. Contour scale for all plots is on the bottom right, in mm day −1 . Each plot uses the native RCM projection, which accounts for the subtle differences in the region covered. Observations are transformed to the NARR grid for comparison.

Description: ABSTRACT Aspects of forecast skill in predicting seasonal characteristics using global climate models (GCMs) are assessed over South Africa. The GCMs output is configured to predict number of rainfall days at South African Weather Service stations exceeding pre-defined threshold values for the austral summer seasons and to predict the rainfall totals of the onset months of the rainy seasons for eight homogeneous rainfall regions of South Africa. Using canonical correlation analysis (CCA) as statistical downscaling technique through model output statistics, the forecast skill levels of coupled ocean–atmosphere and uncoupled atmospheric models are determined through retro-actively generated hindcasts. Both downscaled models have skill in predicting low and high number of rainfall days exceeding pre-defined thresholds for the austral summer seasons as well as rainfall totals of onset months. In addition to the forecast verification results, CCA pattern is performed to determine the dominating atmospheric circulation systems predicted to be controlling rainfall variations for the seasons and months of interest. CCA patterns for both the GCMs indicate that usually when there are anomalously negative (positive) predicted 850 hPa geopotential heights over South Africa, there are anomalously wet (dry) conditions over most parts of South Africa. The work has paved the way for the operational production of seasonal rainfall characteristics over South Africa in real time. This study established that the two climate models run at the South African Weather Service are capable of predicting number of rainfall days exceeding pre-defined thresholds for the austral summer seasons as well as the onset months of the rainy seasons. It was also found that in general similar atmospheric circulation systems are responsible for seasonal rainfall and number of rainfall days within seasons.

Description: We investigate Titan's low- and mid-latitude surface using spectro-imaging near-infrared data from Cassini/VIMS. We use a radiative transfer code to first evaluate atmospheric contributions and then extract the haze and the surface albedo values of major geomorphological units identified in Cassini Synthetic Aperture Radar data, which exhibit quite similar spectral response to the VIMS data. We have identified three main categories of albedo values and spectral shapes, indicating significant differences in the composition among the various areas. We compare with linear mixtures of three components (water ice, tholin-like, and a dark material) at different grain sizes. Due to the limited spectral information available, we use a simplified model, with which we find that each albedo category of regions of interest can be approximately fitted with simulations composed essentially by one of the three surface candidates. Our fits of the data are overall successful, except in some cases at 0.94, 2.03, and 2.79 μm, indicative of the limitations of our simplistic compositional model and the need for additional components to reproduce Titan's complex surface. Our results show a latitudinal dependence of Titan's surface composition, with water ice being the major constituent at latitudes beyond 30°N and 30°S, while Titan's equatorial region appears to be dominated partly by a tholin-like or by a very dark unknown material. The albedo differences and similarities among the various geomorphological units give insights on the geological processes affecting Titan's surface and, by implication, its interior. We discuss our results in terms of origin and evolution theories.

Description: Ancient impact craters with wind-eroded layering on their floors provide a record of resurfacing materials and processes on early Mars. In a 54 km Noachian crater in Terra Sabaea (20.2°S, 42.6°E), aeolian deflation of a friable, dark-toned layer up to tens of meters thick has exposed more resistant, underlying light-toned material. These layers differ significantly from strata of similar tone described in other regions of Mars. The light-toned material has no apparent internal stratification, and visible/near-infrared spectral analysis suggests that it is rich in feldspar. Its origin is ambiguous, as we cannot confidently reject igneous, pyroclastic, or clastic alternatives. The overlying dark-toned layer is probably a basaltic siltstone or sandstone that was emplaced mostly by wind, although its weak cementation and inverted fluvial paleochannels indicate some modification by water. Negative-relief channels are not found on the crater floor, and fluvial erosion is otherwise weakly expressed in the study area. Small impacts onto this crater's floor have exposed deeper friable materials that appear to contain goethite. Bedrock outcrops on the crater walls are phyllosilicate-bearing. The intercrater plains contain remnants of a post-Noachian thin, widespread, likely aeolian mantle with an indurated surface. Plains near Hellas-concentric escarpments to the north are more consistent with volcanic resurfacing. A 48 km crater nearby contains similar dark-over-light outcrops but no paleochannels. Our findings indicate that dark-over-light stratigraphy has diverse origins across Mars and that some dark-toned plains with mafic mineralogy are not of igneous origin.

Description: Science operates best by sharing accurate new knowledge in clear ways. In order to check our assumptions, our methods, and our interpretations of the observations, experiments, analyses, and calculations that we do, we ask others to look at our work. We call this peer review – other experts who were not involved in a given study read and critically evaluate the descriptions of our work. They look for completeness, accuracy, whether work is new, and how clearly we have written the descriptions. We continue to be humbled by the time, effort, and careful insights that our colleagues share with each other through the process of peer review. In 2017, JGR Planets benefited from more than 610 reviews provided by 398 of our peers for papers submitted to the journal. Thank you all for your awesome efforts toward advancing planetary science now and for the future.

Description: Liquid water is one of the most important materials affecting the climate and habitability of a terrestrial planet. Liquid water vaporizes entirely when planets receive insolation above a certain critical value, which is called the runaway greenhouse threshold. This threshold forms the inner most limit of the habitable zone. Here, we investigate the effects of the distribution of surface water on the runaway greenhouse threshold for Earth-sized planets using a three-dimensional dynamic atmosphere model. We considered a 1-bar atmosphere whose composition is similar to the current Earth's atmosphere with a zonally uniform distribution of surface water. As previous studies have already showed, we also recognized two climate regimes: the land planet regime, which has dry low latitude and wet high latitude regions, and the aqua planet regime, which is globally wet. We showed that each regime is controlled by the width of the Hadley circulation, the amount of surface water, and the planetary topography. We found that the runaway greenhouse threshold varies continuously with the surface water distribution from about 130% (an aqua planet) to 180% (the extreme case of a land planet) of the present insolation at Earth's orbit. Our results indicate that the inner edge of the habitable zone is not a single sharp boundary, but a border whose location varies depending on planetary surface condition, such as the amount of surface water. Since land planets have wider habitable zones and less cloud cover, land planets would be good targets for future observations investigating planetary habitability.

Description: ABSTRACT Homogeneous meteorological data are a prerequisite for reliable climatological studies. This paper investigates the homogeneity of wind data from 213 m high Cabauw tower located in The Netherlands. The wind measurements are conducted at 10, 20, 40, 80, 140 and 200 m above ground. The analysed data cover the period from February 1986 to January 1997 and from April 2000 to December 2015. This study presents the first homogeneity analysis of wind data from a tall meteorological mast. Homogeneities of wind speed and wind direction series were investigated independently using the ReDistribution Method. Overall, the wind measurements at Cabauw tower are very homogeneous. The only wind speed inhomogeneity was detected at 200 m above ground and it seems to be, at least to a certain extent, caused by the rapid expansion of the town of Lopik in the 1990s. Lopik's growth to the west, however, only influenced the east winds on the Cabauw tower. Small inhomogeneities in wind direction data were detected at 20, 40 and 80 m levels, whereas a fairly large inhomogeneity was observed at 10 m above ground. Several potential causes of inhomogeneities in wind direction data are discussed, but the major contributor could not be determined with certainty. In addition, the homogeneity of real measurements from Cabauw tower is compared against the synthetically created wind data for Cabauw tower using the Monte-Carlo method of random sampling. The results show that the detected anomalies are not due to the random noise in the time series. The first homogeneity analysis of wind data from a tall meteorological tower. Wind data from the 213 m high Cabauw tower in The Netherlands have several weak wind direction inhomogeneities and a single wind speed inhomogeneity. The potential causes for inhomogeneities determined and discussed.

Description: ABSTRACT North-East Indian Monsoon rainfall (NEIMR) during October–December is of immense socio-economic importance to the agriculture-dependent population in the southeastern peninsular India. NEIMR is subject to extreme year-to-year and intra-seasonal variability that needs to be understood to enhance climate resilience. In this study, we employed hidden Markov model to characterize the spatio-temporal variations of NEIMR at pentad time step and its probability of occurrence during 1982–2014. The results indicated the dominant presence of three rainfall states during the NEIMR season, which were the wet (State-1), coastal wet (State-2), and dry (State-3) states. Seasonal total NEIMR was significantly and positively correlated with the frequency of State-1, whereas it was negatively correlated with that of State-3, indicating a crucial role of the rainfall states in determining water requirements in the southeastern peninsular India. The rainfall states were associated with distinctive atmospheric circulation and surface temperature conditions, particularly the wet (State-1) and dry (State-3) conditions. Wet conditions were characterized by enhanced cyclonic activities and increased moisture convergence at 850 hPa over the southeastern peninsular India and its neighbouring oceanic regions (Bay of Bengal and Indian Ocean). In contrast, dry conditions were associated with anticyclonic circulation and reduced moisture convergence at 850 hPa. The plausible physical mechanisms behind the wet (dry) condition could be that anomalous warmer (cooler) land temperature above 20°N induced lower (higher) sea level pressure anomalies and drove anomalous southwesterly (northeasterly) surface winds over the NEIMR region. These anomalous surface winds and the associated lower level cyclonic (anticyclonic) circulations could enhance (suppress) moisture transport from the convergence regions over the Bay of Bengal and northern Indian Ocean into the southern peninsular India. This study revealed the pentad variability of NEIMR with the classified three rainfall states and identified the key atmospheric circulation and surface temperature conditions linked to these rainfall states. This study revealed the pentad variability of North-East Indian Monsoon rainfall (NEIMR) with the classified rainfall states. The plausible physical mechanisms behind the wet state of NEIMR could be that anomalous warmer land temperature induced lower sea level pressure and drove anomalous southwesterly surface winds. These anomalous surface winds and the associated lower level cyclonic circulations could enhance moisture transport from the convergence regions over the Bay of Bengal and northern Indian Ocean into the southern peninsular India.

Description: We present a new implementation of the hydrological cycle scheme into a general circulation model of the Martian atmosphere. The model includes a semi-Lagrangian transport scheme for water vapor and ice, and accounts for microphysics of phase transitions between them. The hydrological scheme includes processes of saturation, nucleation, particle growth, sublimation and sedimentation under the assumption of a variable size distribution. The scheme has been implemented into the Max Planck Institute Martian general circulation model (MPIŰMGCM) and tested assuming mono- and bimodal lognormal distributions of ice condensation nuclei. We present a comparison of the simulated annual variations, horizontal and vertical distributions of water vapor and ice clouds with the available observations from instruments onboard Mars orbiters. The accounting for bi-modality of aerosol particle distribution improves the simulations of the annual hydrological cycle, including predicted ice clouds mass, opacity, number density, particle radii. The increased number density and lower nucleation rates brings the simulated cloud opacities closer to observations. Simulations show a weak effect of the excess of small aerosol particles on the simulated water vapor distributions.

Description: ABSTRACT The far eastern tropical Pacific experienced a rapid, marked warming in early 2017, causing torrential rains along the west coast of South America with a significant societal toll in Peru and Ecuador. This strong coastal El Niño was largely unpredicted, even a few weeks before its onset, and it developed differently from either central or eastern events. Here we provide an overview of the event, its impacts and concomitant atmospheric circulation. It is proposed that a remotely forced, sustained weakening of the free tropospheric westerly flow impinging the subtropical Andes leads to a relaxation of the southeasterly (SE) trades off the coast, which in turn may have warmed the eastern Pacific throughout the weakening of upwelling in a near-coastal band and the lessening of the evaporative cooling farther offshore. As depicted in this GPM radar image, torrential rains afflicted the otherwise arid coast of Ecuador and Peru from January to April 2017, resulting in a death toll of at least 200 and widespread damage to civil works and infrastructure. The storms occurred in connection with a very strong and largely unpredicted coastal El Niño, whose essential features and plausible trigger mechanism are described here.

Description: ABSTRACT The article demonstrates the impact of atmospheric circulation on the long-term variability of cloudiness (amount and certain cloud genera) in Kraków based on midday observations of the amount and genera of clouds in the period from 1 January 1906 to 31 December 2015. There was found statistically significant (although rather moderate) correlation between circulation indices and the frequency of cloud cover consisting of a single cloud genus or a group of clouds. The 11-year moving averages of frequency of occurrence of one-genus cloud cover show periods of alternating increasing/decreasing trends, some of which are multi-decadal. Decreasing trends, lasting till now, are shown for Cirrostratus , Nimbostratus and Stratus beginning from the 1920s to 1930s and for Altostratus from the 1970s. The Cirrus , Stratocumulus and Cumulus trends are generally increasing from the 1920s, 1950s and 1950s, respectively. The article demonstrates the impact of atmospheric circulation on the long-term variability of cloudiness (amount and certain cloud genera) in Kraków. There was found statistically significant (although rather moderate) correlation between circulation indices and the frequency of cloud cover consisting of a single cloud genus or a group of clouds.

Description: ABSTRACT This study explores the possible causes of rainfall distribution over the two major oceanic raining regions of the north Bay of Bengal (nBoB) and the east equatorial Indian Ocean (eEIO). Despite 17% difference in vertically averaged humidity, there is almost 34% difference in mean rainfall over these two regions. The climatological seasonal [June–September (JJAS)] mean (standard deviation) rainfall over nBoB region is always higher (lower) than that over the eEIO region in all the independent data used. The eEIO region has a much larger percentage of low stratiform and convective rainfall (〈5 mm day −1 ) distribution as compared to nBoB, which is totally opposite in case of moderate stratiform and convective rainfall (〉5 mm day −1 ) distribution. This is further substantiated by a much lower values of outgoing long-wave radiation (OLR) in nBoB (〈200 W m −2 ) as compared to the eEIO (217 W m −2 ) region. Mean Hadley circulation along with relative vorticity/divergence profile supports more intense (gentle) updrafts over nBoB (eEIO) region. Latent heat (LH) is almost three times at the upper level (∼8 km) in case of nBoB as compared to eEIO; however, at the lower level (∼3 km) LH is marginally higher over eEIO region. Microphysical variables, namely cloud ice optical thickness and cloud ice water path, are in much larger quantities over nBoB as compared to eEIO. Furthermore, the cold (warm) rain processes dominate among other microphysical processes over nBoB (eEIO) region. Thus, the interplay among large-scale dynamics, thermodynamics and microphysics is very crucial in the formation of deep clouds and convective rain over the nBoB region and similarly shallow clouds and stratiform rain over the eEIO region. This study will be very useful to guide present-day coupled models for proper representation of different rain components over the nBoB and eEIO region. Schematic of different types of cloud and their associated processes over the (a) nBoB region and (b) eEIO region.

Description: ABSTRACT This article analysed two typhoon seasons (1998 and 2016) over the western North Pacific (WNP) with similar preceding background conditions of the tropical Pacific sea surface temperature (SST). Following the strong El Niño event in the preceding winter, the typhoon season was inactive in 1998 while active in 2016. Compared with 1998, the monsoon trough (MT) in 2016 shifted more eastwards, leading to an increase of the mid-level water vapour, lower-tropospheric relative vorticity and upper-tropospheric divergence, and a decrease of the vertical wind shear. Additionally, the eastwards extension of the MT in 2016 induced more active tropical depression (TD)-type waves than those in 1998. The analysis of the energy budget suggested that the eastwards shift of the MT during the 2016 typhoon season provided increased eddy kinetic energy for typhoon genesis, due to the joint contributions of the meridional shear of the mean zonal winds and the zonal wind convergence over the WNP. Moreover, the WNP entered a La Niña-like SST pattern after July 2016. The relatively slower developing process of this pattern sustained the warmer SST anomalies and the anomalous cyclonic circulation, which the eastwards extension of the MT can be attributed. Hence, compared to 1998, the active typhoon season in 2016 is attributed to the eastwards extension of the MT, more active TD-type wave activities, and slow developing process of a La Niña-like SST pattern in 2016 typhoon season. Numbers of typhoon geneses over the WNP (0–30°N, 100°–180°E) during May–December in 1998 (blue bars) and 2016 (red bars).

Description: ABSTRACT Precipitation data of finer timescale and higher spatial density are crucial for continuous hydrological modelling and flood risk assessment. Disaggregation methods are often used to transform the coarser-timescale precipitation data into finer resolutions. The nonparametric approach based on method of fragments (MOF) has received broad attention in precipitation disaggregation literature, given its superiority in reproducing the at-site statistical attributes. However, a detailed literature review has shown that the MOF-based resampling approaches are mainly focused in the single-site precipitation disaggregation context, which may subject to limitations such as the unavailability of at-site precipitation records and the incapability to preserve the inter-site correlation structure. To address these issues, we propose three resampling approaches based on MOF. The first approach is a single-site interval-based resampling approach which only draws subdaily fragment vectors from at-site record. The second one extends the first one to a regionalized version where subdaily fragment vectors are drawn from both the at-site and neighbouring stations. The third one is a multi-site approach developed to preserve the observed inter-site correlation. The performances of the three methods are evaluated with applications to daily-to-hourly precipitation disaggregation at six rain gauges in Singapore and eight precipitation stations in Wangkuai reservoir catchment in northern China. An elaborate list of performance measures, including standard validation statistics, spatial correlation, inter-day connectivity, annual extreme analysis, and intra-day dry and wet spell characteristics are used to assess the performance. The proposed three methods are shown to be effective in reproducing the at-site attributes, and no significant deterioration of performance is observed when moving from the single-site method to the regionalized and multi-site versions. As expected, the multi-site approach is the only one method that is able to reconstruct the spatial correlation in the disaggregated precipitation field. The approaches can be applied for daily-to-subdaily precipitation disaggregation in different regions. Three resampling approaches, i.e. the singe-site interval-based resampling, the regionalized approach, and the multi-site approach based on method of fragments are proposed for daily-to-hourly precipitation disaggregation. All three approaches are capable of reproducing the at-site statistical attributes. Only the multi-site approach is able to reconstruct the spatial correlation in the disaggregated precipitation field.

Description: A new modeling-based study by Johnson et al. (2017) lends support to the hypothesis that portions of Europa's surface may have been removed by the process of subduction, as suggested by Kattenhorn and Prockter (2014). Using a simple 1D model that tracks the thermal and density structure of a descending ice plate, Johnson et al. show that ice plates with 10% porosity and overall salt contents of ~5%, but which differ in salt content by ~2.5% from the surrounding reference ice shell, are non-buoyant and thus likely to sink through the underlying, convecting portion of the ice shell. The feasibility of subduction in an ice shell is critical to the existence of icy plate tectonics, which is hypothesized to exist at least locally on Europa, potentially making it the only other Solar System body other than Earth with a surface modified by plate tectonics.

Description: Estimates of the Martian elastic lithosphere thickness suggest small values of ∼25 km during the Noachian for the Southern hemisphere and a large present-day difference below the two polar caps (≥300 km in the North and 〉110 km in the South). In addition, young lava flows suggest that Mars has been volcanically active up to the recent past. We run Monte Carlo simulations using a 1D parametrized thermal evolution model to investigate whether a North/South hemispheric dichotomy in crustal properties and composition can explain these constraints. Our results suggest that 55 − 65% of the bulk radioelement content are in the crust, and most of it (43 − 51%) in the Southern one. The Southern crust can be up to 480 kg/m 3 less dense than the Northern one and might contain a non-negligible proportion of felsic rocks. Our models predict a dry mantle and a wet or dry crustal rheology today. This is consistent with a mantle depleted in radioelements and volatiles. We retrieve North/South surface heat flux of 17.1 − 19.5 mW/m 2 and 24.8 − 26.5 mW/m 2 , respectively, and a large difference in lithospheric temperatures between the two hemispheres (170 − 304 K in the shallow mantle). This difference could leave a signature in the seismic signals measured by the future InSight mission.

Description: In 2005, the complex permittivity of the surface of Saturn's moon Titan was measured by the PWA-MIP/HASI (Permittivity Wave Altimetry-Mutual Impedance Probe/Huygens Atmospheric Structure Instrument) experiment on board the Huygens probe. The analysis of these measurements was recently refined but could not be interpreted in terms of composition due to the lack of knowledge on the low-frequency/low-temperature electrical properties of Titan's organic material, a likely key ingredient of the surface composition. In order to fill that gap, we developed a dedicated measurement bench and investigated the complex permittivity of analogs of Titan's organic aerosols called "tholins". These laboratory measurements, together with those performed in the microwave domain, are then used to derive constraints on the composition of Titan's first meter below the surface based on both the PWA-MIP/HASI and the Cassini Radar observations. Assuming a ternary mixture of water-ice, tholin-like dust and pores (filled or not with liquid methane), we find that at least 10% of water ice and 15% of porosity are required to explain observations. On the other hand, there should be at most 50-60% of organic dust. PWA-MIP/HASI measurements also suggest the presence of a thin conductive superficial layer at the Huygens landing site. Using accurate numerical simulations, we put constraints on the electrical conductivity of this layer as a function of its thickness (e.g., in the range 7-40 nS/m for a 7-mm thick layer). Potential candidates for the composition of this layer are discussed.

Description: Major impact events have shaped the Earth as we know it. The Late Heavy Bombardment is of particular interest because it immediately precedes the first evidence of life. The reentry of impact ejecta creates numerous chemical byproducts, including biotic precursors such as HCN. This work examines the production of HCN during the Late Heavy Bombardment in more detail. We stochastically simulate the range of impacts on the early Earth, and use models developed from existing studies to predict the corresponding ejecta properties. Using multi-phase flow methods and finite rate equilibrium chemistry, we then find the HCN production due to the resulting atmospheric heating. We use DSMC to develop a correction factor to account for increased yields due to thermochemical nonequilibrium. We then model 1D atmospheric turbulent diffusion to find the time-accurate transport of HCN to lower altitudes and ultimately surface water. Existing works estimate the necessary HCN molarity threshold to promote polymerization is 0.01 M. For a mixing depth of 100 m, we find that the Late Heavy Bombardment will produce at least 1 impact event above this threshold with probability 24.1% for an oxidized atmosphere and 56.3% for a partially reduced atmosphere. For a mixing depth of 10 m, the probability is 79.5% for an oxidized atmosphere and 96.9% for a partially reduced atmosphere. Therefore, LHB impact ejecta is likely an HCN source sufficient for polymerization in shallow bodies of water, particularly if the atmosphere were in a partially reduced state.

Description: In this study six wooden Stevenson screen configurations (five aspirated, one non-aspirated) were evaluated at the Centre for Atmospheric Research Experiments in Egbert, Ontario, Canada. The field experiment was performed over a 1-year period to evaluate aspirated and non-aspirated Stevenson screen configurations used at the Meteorological Service of Canada’s Automated Weather Stations. The results show the non-aspirated screen is warmer than the aspirated screen duct location by 0.11 °C on average with a significant increase in the maximum daily temperature of 0.22 °C due to radiant heating effects. Temperature differences up to 2.1 °C were observed between the aspirated and non-aspirated screens with a mean increase of 0.46 °C following 30-min periods of mean global radiation greater than 200 W/m 2 and mean wind speed less than 2 m/s. Temperature differences between the two screens are more variable with standard deviations up to 0.3 °C for wind speeds below 2 m/s. The maximum daily temperature for the historic minimum and maximum thermometer locations and upper regions of the aspirated screen is also found to be significantly warmer during radiant heating conditions. The three locations within the aspiration duct provided very similar results with mean differences of −0.02 and −0.01 °C below the probe uncertainty. The aspirated Stevenson screen with motor off produced low overall bias with lower maximum daily temperatures and higher minimum daily temperatures compared to the aspirated screen. Comparison between the historic wooden frame and new aluminium mounting is not significant with the wooden frame cooler by 0.02 °C overall. Differences between the new aluminium and new plastic ducts showed similar results of 0.02 and 0.01 °C overall. The aspirated Stevenson screen configuration is recommended at new Automatic Weather Station installations where AC power is available. The non-aspirated type B Stevenson screen exhibits increased temperature relative to the aspirated screen due to relative heating particularly during periods of global radiation greater than 200 W/m 2 and wind speed less than 2 m/s. For increased wind speeds the influence is diminished due to natural aspiration of the non-aspirated screen. The temperature differences between the two screens are more variable with standard deviations up to 0.3°C for wind speeds below 2 m/s.

Description: This study addresses the impact of projected changes to northeast monsoon on rice yield during rabi season (September–December) in Tamil Nadu by using a three-step approach. First, coarse-resolution global climate models that realistically capture the mean monsoon characteristics were selected. Second, lateral and boundary conditions taken from selected global models’ projections are employed to run a high-resolution regional climate model. Third, climate variables from regional model being fed into panel data regression model. For different scenarios and for mid and end of century projections, in conjunction with projected rainfall, a comprehensive assessment is carried out to underscore the sensitivities of maximum and minimum temperatures under different stages of rice production, viz. vegetative, reproductive and maturity phases, and to the concept of growing degree days (GDD, cumulative heat effect). Irrespective of scenarios, in response to an increase in projected monsoon rainfall and surface temperature conditions, the regression model estimates an increase of rice yield of about 10–12% by mid-century and 5–33% by the end of the century. In the regression model, the baseline coefficients were estimated from observed rainfall and temperature available from India Meteorological Department (IMD). The projected changes in rice yield, however, remain unchanged for baseline coefficients estimated from regional climate model outputs (forced by reanalysis products) rainfall and temperature. The robust results obtained here provide confidence to the findings. This study addresses the impact of northeast monsoon on rice yield during rabi season in Tamil Nadu, southern India by using a high-resolution regional climate model. A comprehensive assessment is performed to underscore the sensitivities of maximum and minimum temperatures and growing degree days under different stages of rice production viz., vegetative, reproductive and maturity phases. Irrespective of scenarios, the regression model estimates an increase of rice yield of about 10–12% by mid-century and 5–33% by the end of the century.

Description: This study demonstrates a methodology to construct short-duration rainfall intensity–duration–frequency (IDF) curves and to quantify the variability in the rainfall intensities for different return periods with respect to the changing climate. A dynamical downscaling approach using the regional climate model (RCM) Weather Research and Forecasting (WRF) has been used to assess present and future climates using the downscaling of an ensemble of three global climate models (GCMs) (CSIRO-ACCESS1.3, MPI-ESM-MR ECHAM6 and NIES-MIROC5) under the Coupled Model Intercomparison Project phase 5 (CMIP5). Furthermore, a statistical approach using the well-known simple scaling method has been applied to extend the 6-hourly WRF precipitation output to the finer temporal scale of 10 min. The short-duration IDF curves were then constructed for the present and future climates under two representative concentration pathway (RCP) scenarios RCP4.5 and RCP8.5. A preliminary examination for this case study over Bac Ninh, an industrial area in the northern Vietnam, shows that there is a substantial increase in short-duration rainfall intensity in the future with respect to the baseline climate. The highest increase is towards the end of the century (2071–2100) ranging from 56 to 61% for a 10- and 100-year return period for 24-hr duration, respectively, while the increase is about 40–45% for the 10-min duration. These results strongly suggest that severe flooding in the future climate over the study region may be likely. The study results might be useful for policymakers and infrastructure planning and for insurance companies around the study area. Projection of simple scaling log–log-scale IDF curve for Bac Ninh using ensemble WRF: return periods (a) 10 years, (b) 25 years, (c) 50 years, (d) 100 years; (1) 2011–2040, (2) 2041–2070, (3) 2071–2100.

Description: In this study, we derive new time-series of monthly-mean surface air temperature for Switzerland that range back to 1864 and represent area-mean conditions over the country and three major sub-regions. The methodology integrates data from a small sample (19 stations) of homogenized long-term series and from a high-resolution (2 km) grid dataset over a short (20 years) period. The statistical combination defines an objective weighting of station data that delivers reliable and time-consistent area-mean estimates, despite coarse and biased coverage with stations in early years. The methodology also quantifies the uncertainty of the estimates. Validation of the method reveals plausible patterns of station weights, and estimation errors of about 0.1 °C, much smaller than inter-annual variations. The new series suggest a warming in Switzerland of almost 1.5 °C from the early-industrial period (1864–1900) till the latest WMO standard period (1981–2010), with a linear trend of 1.29 °C per 100 years between 1864 and 2016. The warming is found to be larger in autumn than in other seasons, larger to the north of the Alps than to the south, and larger below (above) 1000 m asl in winter (summer). In all series, the warming is modulated by inter-decadal variations. Current global temperature datasets exhibit less warming for Switzerland than the present analysis. The pattern of disagreement suggests that a network-wide change in Swiss temperature measurements around 1980 may have been missed in the homogeneity adjustments at global data archives. It is desirable that these archives are better aligned with the latest quality processing of the original data owners. The study derives new time-series of monthly-mean surface air temperature for Switzerland that range back to 1864 and represent area-mean conditions over the country and three major sub-regions. The method integrates data from a small sample of homogenized long-term series and from a high-resolution grid dataset over a short 20-year period. The statistical combination defines an objective weighting of station data that delivers reliable and time-consistent area-mean estimates together with uncertainty information.

Description: ABSTRACT A statistical analysis of 100-year historic Southern Annular Mode (SAM) time series is carried out, for a set of indices calculated by different methods, in view to understanding their value as simple indicators of climate variability and of the physical processes involved, particularly for the early part of the 20th century. Historic SAM time series available in the literature are analysed together with ones calculated using the 20th-century reanalysis. A preliminary analysis and comparison is carried out using standard time and space correlations. Distinct differences are observed in the linear relations between the SAM index time series before and after 1950s. A detailed study is carried out using wavelet transform (WT) analysis, in order to better determine the spectral nature and non-stationarity of the timeseries. The WT spectra reveal an aperiodic, non-stationary evolution in all cases, with differences in the spectral signature of the various SAM indices during the 20th century. Preferred oscillation periods mainly appear between 2 and 20 years. Important differences between the SAM indices arise from different behaviour on the interannual time scale even in more recent years, as well as non-stationarity and phase differences on longer time scales. A wavelet coherency (WTC) analysis between the 20th-century-reanalysis-derived SAM time series shows that differences may also arise for indices calculated from the same data source, particularly during the earlier part of the sample. WTC differences appear at times of perturbed El Niño-Southern Oscillation (ENSO) events. Results using linear as well as a mutual information analysis suggest links between SAM, ENSO, and Pacific-South American patterns of variability, which may depend on the SAM time series definition. Such behaviour could be due to a combination of factors including the geographic coverage of the SAM calculation methods and data quality, as well as ENSO-SAM relationships. A statistical analysis of 100-year historic Southern Annular Mode (SAM) timeseries is carried out, for a set of indices calculated by different methods. A Wavelet transform spectra reveal an aperiodic, non stationary evolution in all historical SAM indices, with differences in the spectral signature during the 20th Century. Results using linear as well as a mutual information analysis suggest links between SAM, ENSO and Pacific-South American patterns of variability, which may depend on the SAM time series definition. Correlation patterns between SAM timeseries and sea-level pressure anomaly timeseries at grid points for SH pressure fields provided by 20CR.

Description: The integrated kinetic energy (IKE) of a tropical cyclone (TC), a volume integration of the surface winds around the centre of the TC, is computed from a comprehensive surface wind (National Aeronautics and Space Administration’s (NASA) cross-calibrated multi-platform [CCMP]) analysis available over the global oceans to verify against IKE from wind radii estimates of extended best-track data maintained by NOAA for the North Atlantic TCs. It is shown that CCMP surface wind analysis severely underestimates IKE largely from not resolving hurricane force winds for majority of the Atlantic TCs, under sampling short-lived and small-sized TCs. The seasonal cycle of the North Atlantic TC IKE also verifies poorly in the CCMP analysis. In this article we introduce proxy IKE (PIKE) based on the kinetic energy of the winds at the radius of the last closed isobar (ROCI), which shows promise for a wide range of TC sizes including the smaller-sized TCs unresolved in the CCMP data set. The composite track density (number of TCs based on non-zero values of 34–50-kt IKE per 2 × 2° cell) plot of North Atlantic TCs for the years 2004–2011 from (a) EBT, (b) CCMP and (c) combined (a) and (b).

Description: Large climate variations have been detected from paleoclimatic records in some regions of South America during the last 500 years. Among them, the Altiplano and the subtropical Andes regions exhibited wetter-than-normal conditions during the 17th century within the paleoclimatic period known as Little Ice Age (LIA). On the other hand, both regions experienced drier-than-normal conditions in the second part of the 20th century in association with the recent global warming period (GWP). This study provides an assessment of the ability of four models of the third phase of the Paleoclimate Modelling Intercomparison Project (PMIP3)/fifth phase of the Coupled Model Intercomparison Project (CMIP5) experiments in reproducing those regional rainfall changes and the associated large-scale circulation features. Climate models can represent qualitatively the temperature changes observed in South America in both periods, LIA and GWP, as compared to the control run, but they do not properly describe the associated precipitation changes. However, they can simulate, in some extent, the large-scale circulation changes that previous works identified as important in driving the precipitation changes in both regions. Therefore, the assessment allows to detect the following changes in LIA (GWP): (a) equatorwards (polewards) displacement of the southern branch of the Hadley cell, in turn associated with wetter (drier) conditions in subtropical south America; (b) negative (positive) upper-level zonal wind changes related with positive (negative) December, January and February (DJF) rainfall changes in the Altiplano; and (c) positive (negative) low-level zonal wind changes associated to positive (negative) JJA rainfall changes in the subtropical Andes, being in turn related to hemispheric wind changes resembling a negative (positive) phase of the southern annular mode. The assessment of PMIP3/CMIP5 experiments allows to detect the following changes in South America during Little Ice Age (recent global warming period): (a) equatorwards (polewards) displacement of the southern branch of the Hadley cell, associated with wetter (drier) conditions in subtropical south America; (b) negative (positive) upper-level zonal wind changes related with positive (negative) DJF rainfall changes in the Altiplano; and (c) positive (negative) low-level zonal wind changes associated to positive (negative) June, July and August (JJA) rainfall changes in the subtropical Andes.

Description: The current version of Laboratoire de Météorologie Dynamique (LMD) Mars GCM (original-MGCM) uses annually repeating (prescribed) CO 2 snow albedo values based on the Thermal Emission Spectrometer observations. We integrate the Snow, Ice, and Aerosol Radiation (SNICAR) model with MGCM (SNICAR-MGCM) to prognostically determine H 2 O and CO 2 snow albedos interactively in the model. Using the new diagnostic capabilities of this model, we find that cryospheric surfaces (with dust) increase the global surface albedo of Mars by 0.022. Over snow-covered regions, SNICAR-MGCM simulates mean albedo that is higher by about 0.034 than prescribed values in original-MGCM. Globally, shortwave flux into the surface decreases by 1.26 W/m 2 , and net CO 2 snow deposition increases by about 4% with SNICAR-MGCM over one Martian annual cycle as compared to original-MGCM simulations. SNICAR integration reduces the mean global surface temperature, and the surface pressure of Mars by about 0.87% and 2.5% respectively. Changes in albedo also show a similar distribution to dust deposition over the globe. The SNICAR-MGCM model generates albedos with higher sensitivity to surface dust content as compared to original-MGCM. For snow-covered regions, we improve the correlation between albedo and optical depth of dust from -0.91 to -0.97 with SNICAR-MGCM as compared to the original-MGCM. Dust substantially darkens Mars' cryosphere, thereby reducing its impact on the global shortwave energy budget by more than half, relative to the impact of pure snow.

Description: Assessing the long-term drought changes is of large interest for understanding the impact of climate change on water resources. Here we have attempted to assess the long-term drought changes (1948–2012) over China using the self-calibrating Palmer drought severity index with Penman–Monteith (scPDSI PM ) and Thornthwaite (scPDSI Th ) methods for potential evapotranspiration (PET) estimations, respectively, so as to understand the impact of different PET methods on drought assessment. Both scPDSI PM and scPDSI Th appear to have drying trends in the humid and transitional climatic regions, which are particularly significant in the north China. Compared to scPDSI PM , the scPDSI Th data have resulted in exaggerated drought severity in the north China since 1980s, and such exaggeration is particularly significant for extreme droughts in terms of the occurrences and the intensity. In the dry climatic regions of northwest China, both scPDSI PM and scPDSI Th appear to exhibit adequate wetting trends; however, both data have shown drying trends of intensity when drought occurs, indicating there are more extreme dry conditions in the context of generally wetting background. Surprisingly, scPDSI PM is found to result in exaggerated droughts rather than scPDSI Th in the northwest China. Both scPDSI PM and scPDSI Th show significant drying trends in the north China, where the scPDSI Th droughts are largely exaggerated. Slightly wetting trends are shown in both scPDSI PM and scPDSI Th in the northwest China, where there are however significantly increased droughts. Either the Penman–Monteith or the Thornthwaite method for PET estimations can lead to exaggerated droughts in different regions in the warming climate. Pixel-wise linear trends for (a) scPDSI PM and (b) scPDSI Th , respectively, during 1948–2012.

Description: Observed sea surface temperature (SST) anomalies in the central eastern equatorial Pacific exhibit two kinds of phase evolution, that is, transition and no-transition, for both the eastern Pacific (EP) and central Pacific (CP) El Niño events. The transition type of El Niño is characterized by a strong decay after its peak and followed by a rapid transition to a La Niña event in the subsequent winter, while the no-transition type of both EP and CP El Niño is featured by a weaker decay after its mature phase and fails to develop a La Niña event in the decaying year. For the EP El Niño, the intensity of the anomalous easterly over the western equatorial Pacific in the transition type is stronger than that in the no-transition type, which is likely determined by the coupling of the Indian Ocean dipole (IOD) during the developing phase and the Indian Ocean basin-wide mode (IOBM) during the decaying phase. For the CP El Niño, larger differences of easterly wind anomalies between the transition type and no-transition type are found over the central eastern equatorial Pacific during the decaying year, which is also likely related to the IOD and IOBM coupling process. In addition, the rapid decay of warm subsurface (80–160 m) temperature anomalies in the central eastern equatorial Pacific during the decaying phases is crucial for the phase transition for the two types of El Niño, together with the eastwards propagation of cold subsurface (100–200 m) temperature anomalies in the western equatorial Pacific. What is more, analyses of the mixed-layer heat budget show that the phase evolution of the EP El Niño depends on dynamic forcing (zonal advection) due to the difference of anomalous mixed-layer ocean currents, while the CP El Niño’s different phase evolution is mainly caused by thermodynamic process, that is, net surface heat flux anomalies. Temporal evolutions of (a) normalized Niño3 index for EP El Niño events and (b) normalized Niño4 index for CP El Niño events. Numbers 0 and 1 in the parentheses denote the developing year and the following year, respectively. Solid and dashed lines indicate transition and no-transition types, respectively. Thick line represents the corresponding composite.

Description: This study demonstrates the fidelity of Climate Forecast System version 2 (CFSv2) in three horizontal resolutions: T62, T126 and T382, during boreal winter. As the Madden–Julian oscillation (MJO) is the major mode of variability during boreal winter, the emphasis of the study is on the fidelity of the models in capturing the MJO variability. CFSv2 shows moderate skill in simulating the intra-seasonal oscillation and the skill is sensitive to the resolution of the model. Boreal winter mean precipitation shows the tendency of the model to overdo the double Intertropical Convergence Zone (ITCZ) that increases with resolution. Twenty to hundred days band-pass-filtered rainfall variances also indicate that the dominant variances are overestimated with increase in resolution. The characteristic eastwards propagation is not captured by the model at all the resolutions. In an attempt to understand the limitation of the model, composites of specific humidity are analysed which show that the model’s moisture profile is rather better represented at lower resolution than the higher ones. Analyses of relative humidity profile as a function of rainfall rates show that all the model resolutions fail to reproduce the lower-level moistening prior to deep convection. Observational studies have shown shallow convection to be responsible for this low-level moistening. Furthermore, analysis of mean stratiform rainfall indicates that spectrum of rainfall variability is not simulated by the model and increasing the resolution could not improve the cloud processes. This study therefore indicates that the fundamental moist convective processes do not improve in the model and neither its bias in capturing the intra-seasonal variability vis-à-vis MJO through increasing resolution. This can therefore be a basis for improving the moist convective processes with emphasis on the improvement of the shallow convection within boundary layer and also for the inclusion of scale dependencies in parameterized processes. Keeping in mind the inclination of modelling community towards high-resolution models, analysis of MJO simulated by CFSv2 at three different horizontal resolutions with the finest being at 28 km is performed which indicates that merely increasing the resolution of the model does improve the skill unless the parameterization schemes are also retuned accordingly or include resolution dependencies.

Description: No abstract is available for this article.

Description: Exceptional dry spells, in this study referred to as very long dry spells (VLDS), are natural hazards to which the Mediterranean region is extremely vulnerable, with socio-economic and environmental impacts. In this study, they are characterized in terms of location, spatial extent, duration, temporal variability and associated atmospheric circulations. The main objective is to assess the performance of five HyMeX/Med-CORDEX regional climate simulations to detect and reproduce VLDS in comparison with the E-OBS observed daily gridded data. Models accurately reproduce the occurrence of precipitation around the Mediterranean Basin, and therefore the occurrence of VLDS, with at least 51% of the E-OBS VLDS reproduced by the regional simulations. They also accurately simulate the spatio-temporal characteristics. A second objective is to identify the synoptic atmospheric patterns associated with VLDS. A clustering analysis shows that all models accurately reproduce the main VLDS spatial patterns, associated with anticyclonic conditions above the affected regions. The simulated VLDS occurrence is strongly related to the amplitude of the sea level pressure and 500-hPa geopotential height anomalies as well as the location of the maximum anomalies. All VLDS events are associated with anticyclonic conditions except those occurring in the eastern Mediterranean, where they are generally not associated with a specific meteorological event but with the usual summer weather regime. The main objective is to assess the performance of five HyMeX/Med-CORDEX regional climate simulations to detect and reproduce VLDS in comparison with the E-OBS observed daily gridded data. Models well reproduce the occurrence of precipitation around the Mediterranean Basin, and therefore the occurrence of VLDS and their spatio-temporal characteristics. However, models tend to detect VLDS slightly shorter and less extent compared to the E-OBS. Fraction of VLDS days at each grid point with respect to the total studied days in the whole Mediterranean domain computed from the E-OBS data set (a), and simulated biases for CCLM4 (b), Reg_CM4 (c), ALADIN52 (d), LMDZ4 model (e) and LMDZ4-NEMOMED8 model (f). The grey shaded area indicates the absence of data for the analysis.

Description: The giant impact hypothesis remains the leading theory for lunar origin. However, current models struggle to explain the Moon's composition and isotopic similarity with Earth. Here we present a new lunar origin model. High-energy, high-angular momentum giant impacts can create a post-impact structure that exceeds the corotation limit (CoRoL), which defines the hottest thermal state and angular momentum possible for a corotating body. In a typical super-CoRoL body, traditional definitions of mantle, atmosphere and disk are not appropriate, and the body forms a new type of planetary structure, named a synestia. Using simulations of cooling synestias combined with dynamic, thermodynamic and geochemical calculations, we show that satellite formation from a synestia can produce the main features of our Moon. We find that cooling drives mixing of the structure, and condensation generates moonlets that orbit within the synestia, surrounded by tens of bars of bulk silicate Earth (BSE) vapor. The moonlets and growing moon are heated by the vapor until the first major element (Si) begins to vaporize and buffer the temperature. Moonlets equilibrate with BSE vapor at the temperature of silicate vaporization and the pressure of the structure, establishing the lunar isotopic composition and pattern of moderately volatile elements. Eventually, the cooling synestia recedes within the lunar orbit, terminating the main stage of lunar accretion. Our model shifts the paradigm for lunar origin from specifying a certain impact scenario to achieving a Moon-forming synestia. Giant impacts that produce potential Moon-forming synestias were common at the end of terrestrial planet formation.

Description: Prediction of climate extremes is challenging, especially for non-Gaussian extremes in urban areas where the majority of people live, since the Gaussian assumption used in linear regression is violated and the urbanization effect needs to be considered. In this study, the first-order difference method is introduced to take these difficulties into account. Statistical prediction of the non-Gaussian annual occurrence of hot days in downtown Hong Kong, which is highly urbanized, is used to illustrate this method. With the help of the first-order difference of the annual occurrences, which follows a Gaussian distribution, the difference series is used as the predictant to find predictors and to construct a prediction model by using traditional linear regression. The difference is first predicted and is then added to the observed value at the preceding time to obtain the predicted annual occurrence. The historical urbanization effect is thus obtained directly from the observations at the preceding time. The prediction results are found desirable. The broad application potential and conditions in which this method should be used are also discussed. Time series of annual occurrence of hot days (blue curve) in Hong Kong for the period 1947–2016 (a) and its normality tests (b, c). In (a), the linear trend estimated by the WS2001 (red line) and the 11-year running mean (black curve) are also plotted. In (b), the blue bars are the target data under testing and the red line is the fitted Gaussian distribution. The p 〉 .05 in the Jarque–Bera test indicates that the target data are normally distributed. In the quantile–quantile plot (c), red circles indicate the distribution of the target data and the black solid lines represent the Gaussian distribution, with the 95% confidence intervals shown as black dashed lines. The approximate linearity of the circles suggests that the target data are normally distributed. (d), (e) and (f) are the same as (a), (b) and (c), respectively, but for the year-to-year increment of hot days.

Description: Credible information about the properties and changes of extreme events on the regional and local scales is of prime importance in the context of future climate change. Within the EU-COST Action VALUE a comprehensive validation framework for downscaling methods has been developed. Here we present validation results for extremes of temperature and precipitation from the perfect predictor experiment that uses reanalysis-based predictors to isolate downscaling skill. The raw reanalysis output reveals that there is mostly a large bias with respect to the extreme index values at the considered stations across Europe, clearly pointing to the necessity of downscaling. The performance of the downscaling methods is closely linked to their specific structure and setup. All methods using parametric distributions require non-standard distributions to correctly represent marginal aspects of extremes. Also, the performance is much improved by explicitly including a seasonal component, particularly in case of precipitation. With respect to the marginal aspects of extremes the best performance is found for model output statistics (MOS), weather generators (WGs) as well as perfect prognosis (PP) methods using analogues. Spell-length-related extremes of temperature are best assessed by MOS and WGs, spell-length-related extremes of precipitation by MOS and PP methods using analogues. The skill of PP methods with transfer functions varies strongly across the methods and depends on the extreme index, region and season considered. Indices, codes and associated performance measures for extremes of precipitation and temperature ( T min  = minimum temperature; T max  = maximum temperature).

Description: We present the Caribbean's Virgin Islands’ climate variability over the last 60 years from indices of extreme temperature and precipitation, as well as their quantitative support for a recent climatic shift (1983.2 ± 5.5 years). The region's climate indices (defined via time series averages) and trends (defined via linear least squares regression fitting) of extreme temperature and precipitation were cross-examined from 1952, 1961, 1978, and 1983–2014 to diagnose: the area's climatic extremes; a climatic transition's role in assessing decadal climate anomaly rates; and to provide an analytically independent test of the transition's existence. Analyses relied on the use of varying physical constraints to include weighting from statistical and non-statistical uncertainties in our climatic outcomes. We report that diurnal warming and enhanced precipitation accompanied each interval, however, non-negligible deviations existed in comparisons between the same anomalies in any 2 intervals. Our Virgin Islands’ long (1952, 1961–2014) versus short (1978, 1983–2014) climate variation comparisons provide evidence for the manifestation of decadal (or longer) shifts, and thus, biases, in recent Caribbean reports. Our climatic transition's overlap with the renowned 1976/1977 Pacific event insinuates a local Caribbean teleconnection, and contributes to the evidence growing globally for 1980s’ shifts in an abundance of feedback measures of Earth's energy budget. We present the Virgin Islands' climate variability over the last 60 years, from indices of extreme temperature and precipitation, as well as their quantitative support for a recent climate shift. This work diagnoses a shift's role in accessing decadal climate anomalies, and reveals biases in recent Caribbean climate reports. The shift's overlap with the renowned 1976/1977 Pacific event insinuates a teleconnection, and contributes to the evidence growing globally for 1980s' shifts in an abundance of feedback measures of Earth's energy budget.

Description: The extreme El Niño events, such as those which occurred in 1982–1983, 1997–1998, and 2015–2016, exerted devastating impacts in many parts of the globe. Hence, it is crucial to understand the precursors of such extreme events. Nevertheless, each El Niño event has its own characteristics even in the initiation. Here, we show that the development of early-spring equatorial central Pacific warming forced by the increased solar radiation due to a suppressed convection was a crucial factor in developing the 1982–1983 extreme El Niño event. The central Pacific warming anomalies in the spring of 1982 were induced by atmospheric subsidence connected to the northern subtropical Pacific convection, subsequently reinforced by a reduced evaporative cooling via westerly anomalies. On the other hand, springtime warming anomalies over the equatorial central and eastern Pacific regions during other extreme El Niño events were induced mainly by oceanic dynamical processes. Composite maps of the 925-hPa level anomalous (a) zonal wind (U925, shadings, at intervals of 0.1 m/s) and horizontal winds (UV925, vectors, wind speed 〉 0.5 m/s highlighted by thickened black vectors) and (b) upper ocean temperature (indicating the upper ocean heat content, OHC, shadings, at intervals of 0.1 °C) averaged over the equatorial band of 5°S–5°N during FMA(0) for the 20 El Niño events for the period of 1958–2016. (c) Relationship between the WP-wind ( x -axis) and OHC ( y -axis) indices during FMA(0) for the respective El Niño events (see Section 2). Scatters indicate each of the 20 El Niño events and the size of markers is proportional to the El Niño amplitudes as following the Niño-3.4 index intensities during DJF(0/1) (c.f., Figure S1). Extreme (moderate) El Niño events are marked with red (blue) markers. Temporal evolutions of the 3-month averaged (d) Niño-4 and (e) Niño-3.4 indices for the three extreme El Niño events of 1982–1983 (red), 1997–1998 (blue), and 2015–2016 (purple) and the 17 moderate El Niño events averaged anomalies (black) with the 95% confidence intervals shaded on the original anomalies. See Section 2 for the El Niño event classification. The lags are taken 2 and 1 year before (Yr(−1) and Yr(0)) and 1 year after (Yr(+1)) El Niño event has peaked. Winds including U925, UV925, and WP-wind index are from NCEP R1 data; OHC and OHC index are from SODAv2.2.4 and GODAS (only for the 2015–2016 El Niño event) data; Niño-4 and Niño-3.4 indices are from ERSSTv4 data.

Description: Seasonal snow cover over the Tibetan plateau (TP) has unique features in terms of global snow cover distribution because of the high mountains and vital surface water storage functions in non-humid regions of Southwest China and surrounding Asian countries. Limited by the complex topography and relatively low spatial resolution of satellite observations, the characteristics of snow phenology and the factors for snow phenology changes remain still unclear. Using multisource data for the period 2001–2014, this study quantifies the climatology of snow phenology and explores its attribution factors. The results show that the snow onset date ( D o ) and snow end date ( D e ) were 4.9 (±7.7) and 108.1 (±5.9) in day of year (DOY), respectively, and the snow duration days ( D d ) were 103.2 (±13.4) over the TP during the study period. The characteristics of satellite observed D d was similar to subzero temperature days derived from ground observations. The 14-year anomalies in snow phenology features regional disparity over the TP, with increased D d in the central TP and shortened D d in the Tarim River, endorheic drainage basins, and upper reaches of the Brahmaputra River. In contrast to previous findings in northern mid-latitudes, changes in D d over the TP during 2001–2014 were mainly induced by anomalies in D o , which can be further attributed to the declines in accumulation season temperature over the TP. Seasonal snow cover over the Tibetan plateau (TP) has unique features in terms of global snow cover distribution maps. Limited by its complex topography and spatial resolution of satellite snow products, the characteristics of snow phenology and the factors for snow phenology changes are still not clear. By using fine resolution satellite observations and ground records, this study investigate the climatology and anomaly of snow phenology over the TP and explored its attribution factors for the period 2001–2014, which is important in probing the response of snow cover to climate change over the TP.