ALBERT

Description: Tibetan glaciers are substantially influenced by smoke aerosols derived from intensive biomass burning (BB) emissions in surrounding regions. However, knowledge regarding the impact of smoke aerosols on Tibetan glaciers is limited. Here we present levoglucosan records extracted from two southeastern Tibetan (SET) glaciers. We found that Zuoqiupu (ZQP) Glacier, situated on the windward side of the mountains, is more strongly affected by BB aerosols when compared with Cuopugou (CPG) Glacier on the leeward side. On ZQP Glacier, the highest levoglucosan concentration was detected at an elevation near the equilibrium line altitude (ELA). The injection height of smoke plumes and the actions of post-depositional processes on the glacier surface determined the distribution patterns of levoglucosan concentrations at different altitudes. Spatiotemporal variability in levoglucosan and black carbon (BC) distributions after deposition may be caused by the different source characteristics and by different post-depositional geochemical behaviors on the glacier surface. Intense wildfires can lead to extremely high concentrations (higher than 25 ng mL -1 ) of black carbon in ice near the surface of SET glaciers, and can therefore play an important role in glacial melt during the pre-monsoon season.

Description: Tropospheric O 3 has been decreasing across much of the eastern U.S. but has remained steady or even increased in some western regions. Recent increases in VOC and NO x emissions associated with the production of oil and natural gas (O&NG) may contribute to this trend in some areas. The Northern Front Range of Colorado has regularly exceeded O 3 air quality standards during summertime in recent years. This region has VOC emissions from a rapidly developing O&NG basin and low concentrations of biogenic VOC in close proximity to urban-Denver NO x emissions. Here, VOC OH reactivity (OHR), O 3 production efficiency (OPE), and an observationally constrained box model are used to quantify the influence of O&NG emissions on regional summertime O 3 production. Analyses are based on measurements acquired over two summers at a central location within the Northern Front Range that lies between major regional O&NG and urban emission sectors. Observational analyses suggest that mixing obscures any OPE differences in air primarily influenced by O&NG or urban emissions sectors. The box model confirms relatively modest OPE differences that are within the uncertainties of the field observations. Box model results also indicate that maximum O 3 at the measurement location is sensitive to changes in NO x mixing ratio but also responsive to O&NG VOC reductions. Combined, these analyses show that O&NG alkanes contribute over 80% to the observed carbon mixing ratio, roughly 50% to the regional VOC OHR, and approximately 20% to regional photochemical O 3 production.

Description: Temporal variability in the vertical distribution of aerosol optical thickness (AOT) derived from the 0.532 µm aerosol extinction coefficient is described using Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) observations over eight and a half years (June 2006 – December 2014). Temporal variability of CALIOP column-integrated AOT is largely consistent with total-column AOT trends from several passive satellite sensors, such as the Moderate Resolution Imaging Spectroradiometer (MODIS), Multi-angle Imaging Spectroradiometer (MISR), and the Sea-viewing Wide Field-of-view Sensor (SeaWiFS). Globally, a 0.0002 AOT per year positive trend in deseasonalized CALIOP total-column AOT for daytime conditions is attributed to corresponding changes in near-surface (i.e., 0.0-0.5 km or 0.5-1.0 km above ground level [AGL]) aerosol particle loading, while a -0.0006 AOT per year trend during nighttime is attributed to elevated (i.e., 1.0-2.0 km or 〉 2.0 km AGL) aerosols. Regionally, increasing daytime CALIOP AOTs are found over Southern Africa and India, mostly due to changes in aerosol loading at the 1.0-2.0 km and 0.0-0.5 km AGL layers, respectively. Decreasing daytime CALIOP AOTs are observed over Northern Africa, Eastern U.S., and South America (due mostly to elevated aerosol loading), while the negative CALIOP AOT trends found over Eastern China, Europe, and Western U.S. are due mostly to aerosol layers nearer the surface. To our knowledge, this study is the first to provide both a globally comprehensive estimation of the temporal variation in aerosol vertical distribution and insight into passive sensor column AOT trends in the vertical domain.

Description: A large-scale precipitation tracking (LPT) method is developed to track convection and precipitation associated with the MJO using the TRMM 3B42 rainfall data from October-March 1998-2015. LPT uses spatially smoothed 3-day rainfall accumulation to identify and track precipitation features in time with a minimum size of 300, 000 km 2 and time continuity at least 10 days. While not all LPT systems (LPTs) are attributable to the MJO, among the 199 LPTs, there were 42 with a mean eastward propagation of at least 2 m s -1 , which are considered to be MJO convective initiation events. These LPTs capture the diversity of the MJO convection, which is not well depicted by the Realtime Multivariate MJO (RMM) index or the OLR MJO Index (OMI). During the 17 years, there were 17 instances out of 45 with a MJO signature in the RMM without eastward propagating LPTs. Among the 42 eastward propagating LPTs, 24 propagated across the Maritime Continent (MC), which confirms the MC barrier effect. Among the cases that crossed the MC from the Indian Ocean to the west Pacific (MC-crossing), 18 (75%) had a significant MJO signature in the RMM index. In contrast, only 6 (33%) of the non-MC-crossing cases occurred with a RMM MJO signal. There is a significant seasonal and interannual variability with MC-crossing LPTs occurring in December more commonly than other months. More MC-crossing events were observed during La Niña than El Niño, which is consistent with observations of stronger and more frequent MJO events identified by RMM during La Niña years.

Description: Here we assess estimates of atmospheric evaporative demand over China in twelve state-of-the-art Global Climate Models (GCMs) against observed D20 pan evaporation ( E pan ) over the period 1961–2000. To do that, we use an energy-relevant and physical-based approach, namely PenPan model, to comprehensively evaluate GCM performance with respect to their ability to simulate annual, seasonal and monthly statistics of E pan (and its radiative and aerodynamic components, E p , R and E p , A ). The results indicated that most GCMs generally captured the spatial pattern and seasonal cycle of E pan , E p , R and E p , A . However, regional means of annual and monthly E pan , E p , R and E p , A were underestimated by most GCMs mainly due to negatively biased surface air temperature ( T a ) and vapour pressure deficit ( vpd ) outputted/simulated by the GCMs. Overall, the discrepancies among GCMs in estimating the regional statistics (regional means and seasonal cycles) of E p , A were relatively larger than that ofE p , R , which indicates considerable uncertainties in the calculation of the aerodynamic component of evaporation based on the GCM outputs. Moreover, a few GCMs captured negative trends of regional mean annual and seasonal E pan , E p , R and E p , A well over the period 1961– 2000, but most showed positive trends. The underestimation of net radiation ( R n ) and overestimation of wind speed at 2 meters ( u 2 ) in most GCMs may, to some extent, accentuate/compensate the negative biases in GCM-estimated annual and seasonal E pan , E p , R and E p , A . The results demonstrate the importance of incorporating observation of pan evaporation and well validated PenPan model to evaluate GCMs performance on atmospheric evaporative demand that is relevant to projections of future drought and regional water-energy budgets.

Description: A meteorological model requires accurate initial conditions and boundary conditions to obtain realistic numerical weather predictions. The land surface controls the surface heat and moisture exchanges, which can be determined by the physical properties of the soil and soil state variables, subsequently exerting an effect on the boundary layer meteorology. The initial and boundary conditions of soil moisture are currently obtained via NCEP FNL (Final) Operational Global Analysis data, which are collected operationally in 1 degree by 1 degree resolutions every six hours. Another input to the model is the soil map generated by the FAO-UNESCO soil database, which combines several soil surveys from around the world. Both soil moisture from the FNL analysis data and the default soil map lack accuracy and feature coarse resolutions, particularly for certain areas of China. In this study, we update the global soil map with data from Beijing Normal University in 1 km by 1 km grids and propose an alternative method of soil moisture initialization. Simulations of the Weather Research and Forecasting Model show that spinning-up the soil moisture improves near-surface temperature and relative humidity prediction using different types of soil moisture initialization. Explanations of that improvement and improvement of the planetary boundary layer height in performing process analysis are provided.

Description: No abstract is available for this article.

Description: We use a single-particle aerosol mass spectrometer (SPAMS) coupled with a ground-based counterflow virtual impactor (GCVI) to measure the chemical compositions of individual submicron fog droplet residues. This is the first report of single-particle mass spectrometry measurements of fog droplet residual particles at ground level in an urban area. We show that most of the fog droplet residues were composed of elemental carbon (EC) (67.7%), followed by K-rich (19.2%) and mineral dust/metal (12.3%) particles. The predominance of EC-containing particles demonstrated that these particles could be effective fog nuclei and highlights the important influence of anthropogenic emissions on regional climate system. Compared with interstitial and ambient aerosols, nitrate was enhanced, sulfate was depressed, and ammonium- and organics-containing particles were hardly found in the fog droplet residues during fog events, suggesting that dust and metal particles containing nitrate may be preferentially activated and that ammonium and organics may not play important roles in fog formation in Guangzhou. We also present direct observational evidence that trimethylamine (TMA) and hydroxymethanesulfonate (HMS) are not found within fog droplet residues, although we previously observed enhanced gas-to-particle partitioning of these compounds by fog processing. Additionally, higher fraction or intensities of [K] + , [Fe] + and [SiO 3 ] - were found in fog droplet residues than in ambient and interstitial particles.

Description: This paper presents an analysis of the relationship between land surface temperatures (LST) and screen-level air temperatures (T2m) using in situ observations from 19 Atmospheric Radiation Measurement (ARM) deployments located in a range of geographical regimes. The diurnal cycle is resolved using one-minute observations: a particular focus of the study is on the relationship between daily extremes of LST (LSTmax, LSTmin) and T2m (Tmax, Tmin). Temperature differences are analysed with respect to cloud, wind speed and snow cover. Under cloud-free, low wind speed conditions, day time LST is often several degrees Celsius (°C) higher than T2m at low-to-mid latitudes, and at high latitudes during the summer months. In contrast, LST and T2m are often close (e.g. within 2 °C) under cloudy and/or moderate-to-high wind speed conditions, or when solar insolation is low or absent. LSTmin and Tmin are generally well correlated (r 〉0.8, often r 〉0.9), while seasonal correlations between LSTmax and Tmax are weaker (r 〉0.6, often r 〉0.8). At high latitudes, LST and T2m are well coupled in Spring/Autumn/Winter; the relationship between LST and T2m tends to weaken with decreasing latitude. The timing of daily extremes is also investigated and it is found that LSTmin and Tmin typically occur close to sunrise, with Tmin occurring slightly after LSTmin. LSTmax occurs close to solar noon, with Tmax typically occurring 1-3 hours later. This study will inform temperature data users on differences between LST and T2m, and aid development of methods to estimate T2m using satellite LSTs.

Description: Satellite remote sensing of Precipitable Water Vapor (PWV) is essential for monitoring moisture in real-time for weather applications, as well as tracking the long-term changes in PWV for climate change trend detection. This study assesses the accuracies of the current satellite observing system, specifically the National Aeronautics and Space Administration (NASA) Atmospheric Infrared Sounder (AIRS) v6 PWV product and the European Organization for the Exploitation of Meteorological Satellite Studies (EUMETSAT) Infrared Atmospheric Sounding Interferometer (IASI) v6 PWV product, using Ground-Based SuomiNet Global Positioning System (GPS) network as truth. Elevation-corrected collocated matchups to each SuomiNet GPS station in North America and around the world was created and results were broken down by station, ARM-region, climate zone, and latitude zone. The greatest difference, exceeding 5%, between IASI and AIRS retrievals occurred in the tropics. Generally, IASI and AIRS fall within a 5% error in the PWV range of 20-40 mm (a mean bias less than 2 mm), with a wet bias for extremely low PWV values (less than 5 mm) and a dry bias for extremely high PWV values (greater than 50 mm). The operational IR satellite products are able to capture the mean PWV but degrade in the extreme dry and wet regimes.

Description: We use data from the Aeronomy of Ice in the Mesosphere (AIM) mission and simulations using the Whole Atmosphere Community Climate Model (WACCM) to determine the impact of the January 23-30, 2012 solar proton event (SPE) on polar mesospheric clouds (PMCs) and mesospheric water vapor. We see a small heating and loss of ice mass on 26 January that is consistent with prior results, but is not statistically significant. We also find a previously unreported but statistically significant ~10% increase in ice mass and in water vapor in the sublimation area in the model that occurs in the 7 to 14 days following the start of the event. The magnitude of the response to the January 2012 SPE is small compared to other sources of variability like gravity waves and planetary waves; however, sensitivity tests suggest that with larger SPEs this delayed increase in ice mass will increase, while there is little change in the loss of ice mass early in the event. The PMC response to SPEs in models is dependent on the gravity wave parameterization, and temperature anomalies from SPEs may be useful in evaluating and tuning gravity wave parameterizations.

Description: Extreme precipitation events, commonly associated with 'Atmospheric Rivers', are projected to increase in frequency and severity in western North America, however, the intensity and landfall position are difficult to forecast accurately. As the isotopic signature of precipitation has been widely utilized as a tracer of the hydrologic cycle and could potentially provide information about key physical processes, we utilize both climate and precipitation isotope data to investigate these events in California from 2001–2011. Although individual events have extreme isotopic signatures linked to associated circulation anomalies, the composite across all events unexpectedly resembles the weighted mean for the entire study period, reflecting diverse moisture trajectories and associated teleconnection phases. We document that 90% of events reaching this location occurred during the negative Arctic Oscillation, suggesting a possible link with higher latitude warming. We also utilize precipitation data of extreme precipitation events across the entire Western US to investigate the relationships between key tropical and Arctic climate modes known to influence precipitation in this region. Results indicate the wettest conditions occur when the negative Arctic Oscillation, negative Pacific North American pattern, and positive Southern Oscillation are in sync and that precipitation has increased in the Southwestern US and decreased in the Northwestern US relative to this phase combination's 1979–2011 climatology. Furthermore, the type of El Niño Southern Oscillation event, Central Pacific or Eastern Pacific, influences the occurrence, landfall location, and isotopic composition of precipitation.

Description: The snow-albedo feedback (SAF) strongly influences climate over mid-latitude mountainous regions. However, over these regions the skill of regional climate models (RCMs) at simulating properties such as snow cover and surface albedo is poorly characterized. These properties are evaluated in a pair of 7-year long high-resolution RCM simulations with the Weather Research and Forecasting (WRF) model over the central Rocky Mountains. Key differences between the simulations include the computational domain (regional vs. continental) and land surface model used (Noah vs. Noah-MP). Simulations are evaluated against high-resolution satellite estimates of snow cover and albedo from the Moderate Resolution Imaging Spectroradiometer (MODIS). Both simulations generally reproduce the observed seasonal and spatial variability of snow cover, but also exhibit important biases. One simulation substantially over-predicts sub-pixel fractional snow cover over snowy pixels (by up to 0.4) causing large positive biases in surface albedo, likely due in part to inadequate representation of canopy effects. The other simulation exhibits a negative bias in areal snow extent (as much as 19% of the analysis domain). Surface measurements reveal large positive biases in snow albedo (exceeding 0.2) during late spring caused by neglecting radiative effects of impurities deposited onto snow. Semi-idealized climate change experiments show substantially different magnitudes of SAF-enhanced warming in the two simulations that can be tied to the differences in snow cover in their control climates. More-confident projections of regional climate change over mountains will require further work to evaluate and improve representation of snow cover and albedo in RCMs.

Description: Using a set of fully-coupled climate model simulations, the response to partial deforestation over the Amazon due to agricultural expansion has been analyzed. Three variations of 50% deforestation (all of western half, all of eastern half, and half of each grid box) were compared with total deforestation to determine the degree and character of non-linearity of the climate response to partial deforestation. A metric is developed to quantify the degree and distribution of non-linearity in the response, applicable to any variable. The metric also quantifies whether the response is saturating or accelerating, meaning either significantly more or less than 50% of the simulated response to total deforestation is attained at 50% deforestation. The spatial structure of the atmospheric response to Amazon deforestation reveals large areas across the tropics that exhibit a significant non-linear component, particularly for temperature and geopotential height. Over the domain between 45°S-45°N across all longitudes, 50% deforestation generally provides less than half of the total response to deforestation over oceans, indicating the marine portion of climate system is somewhat resilient to progressive deforestation. However, over continents there are both accelerating and saturating responses to 50% Amazon deforestation, and the response is different depending on whether the eastern or western half of Amazonia is deforested, or half of the forest is removed uniformly across the region.

Description: This study expands upon the results of Bang and Zipser [2015], which demonstrated that oceanic precipitation features with lightning tended to be over ten times larger and more stratiform than those over continents, and suggested the hypothesis that some form of external forcing is acting in ways that lead to both larger features and stronger updrafts over tropical oceans. In this work, we evaluate this hypothesis by using reanalysis data to compare large-scale vertical motion and thermodynamic data for RPFs in archetypal land and ocean regimes in the Congo and Central Pacific. We then expand our study to the entire TRMM domain (35°S to 35°N) over all seasons. Over the ocean, there is a tendency for stronger large-scale upward motion, linear organization of the convective region, and larger precipitation areas in systems with lightning. By comparison, over land, features with lightning tend to be smaller, in environments of higher instability, with little difference in large-scale vertical motion. Expanding our analysis to 21 different regions, we highlight those in which seasonal synoptic patterns and water temperature gradients lead to distributions that are exceptions to the findings that ocean storms with lightning tend to be larger and more mature than land storms with lightning. These findings support the hypothesis that most land storms have updrafts sufficiently strong to develop lightning in their early growth stages, while ocean storms require large-scale ascent and growth into mesoscale convective systems before convective scale updrafts become strong enough to provide the necessary conditions for lightning.

Description: The temporal and spatial slopes of water isotope-temperature relations are studied for the last 21,000 years over the middle and high latitudes using a series of snapshot simulations of global climate and water isotopes in the isotope-enabled atmospheric model isoCAM3. Our model simulation suggests that both the temporal slope and spatial slope remain largely stable throughout the last deglaciation. Furthermore, the temporal slope can vary substantially across regions. Nevertheless, on average, and most likely, the temporal slope is about 0.3‰∙ °C − 1 , and is about half of the spatial slope. Finally, the relation between temporal and spatial slopes is understood using a semi-empirical equation that is derived based on both the Rayleigh distillation and a fixed spatial slope. The slope equation quantifies the Boyle's mechanism and suggests that the temporal slope is usually smaller than the spatial slope in the extratropics mainly because of the polar amplification feature in global climate change, such that the response in local temperature at mid- and high-latitudes is usually greater than that in the total equivalent source temperature.

Description: Using a coastal ice core collected from Prince of Wales (POW) Icefield on Ellesmere Island, we investigate source regions of sea ice-modulated chemical species (methanesulfonic acid (MSA) and chloride (Cl - )) to POW Icefield, and the influence of large-scale atmospheric variability on the transport of these marine aerosols (1979–2001). Our key findings are: (1) MSA in the POW Icefield core is derived primarily from productivity in the sea-ice zone of Baffin Bay and the Labrador Sea, with influence from waters within the North Water (NOW) polynya, (2) sea-ice formation processes within the NOW polynya may be a significant source of sea-salt aerosols to the POW core site, in addition to offshore open water source regions primarily in Hudson Bay, and (3) the tropical Pacific influences the source and transport of marine aerosols to POW Icefield through its remote control on regional winds and sea-ice variability. Regression analyses during times of MSA deposition reveal sea level pressure (SLP) anomalies favorable for opening of the NOW polynya, and subsequent oceanic dimethyl sulfide production. Regression analyses during times of Cl - deposition reveal SLP anomalies that indicate a broader oceanic region of sea-salt sources to the core site. These results are supported by SMMR- and SSM/I-based sea-ice reconstructions and air mass transport density analyses, and suggest the marine biogenic record may capture local polynya variability, while sea-salt transport to the site from larger offshore source regions in Baffin Bay is likely. Regression analyses show a link to tropical dynamics via an atmospheric Rossby wave.

Description: The effects of two types of ENSO events on tropical ozone (O 3 ) variations from 1982 to 2010, and the mechanisms underlying these effects, were analyzed using observations and model simulations. Tropospheric column O 3 anomalies (TCOA) during canonical El Niño were different from El Niño Modoki. Absolute TCOA values are larger during canonical El Niño than during El Niño Modoki in most regions. La Niña events were not separated into the different types because of their similarity in terms of sea surface temperature patterns. TCOA in La Niña showed a reversed dipole from canonical El Niño. During canonical El Niño, anomalous downward motion together with suppressed convection weakened O 3 outflow from the troposphere, causing an increase in tropospheric O 3 over western Pacific. Over central and eastern Pacific, decreased O 3 concentrations resulted primarily from a change in net chemical production of O 3 . The change in net O 3 chemical production relates to increased levels of HOx under wetter condition. During El Niño Modoki, transport and chemical fluxes were similar but weaker than during canonical El Niño. During La Niña, O 3 anomalies and transport fluxes were the opposite of those during the El Niño Modoki. Stratospheric O 3 played a key role in the development of O 3 anomaly above 250 hPa during ENSO events, contributing 〉30% to the O 3 anomalies. The change in free tropospheric O 3 affected the O 3 anomaly from 850 hPa to 200 hPa (60% of O 3 anomaly). The contribution of O 3 from planetary boundary layer was concentrated at the surface, with a contribution of 〈15%.

Description: The performance of Beijing Climate Center Climate system model (BCC_CSM) with 2 horizontal resolutions in simulating the precipitation seasonal variation over Eastern China has been evaluated. The possible reasons related to the differences in the simulations of BCC_CSM1.1 m model with fine resolution and BCC_CSM1.1 model with coarse resolution also have been addressed and discussed. Results show that the the improved simulation of the timing and amount of precipitation in dry seasons except for larger biases during rainy seasons can be noted in BCC_CSM1.1 m model relative to BCC_CSM1.1 model. The occurrence time of the precipitation annual peaks in BCC_CSM1.1 m model shows better agreements with the observation compared to BCC_CSM1.1 model. Mechanism analysis indicates that BCC_CSM1.1 produced earlier East Asian summer monsoon (EASM) onset and northward jump of Western Pacific subtropical high (WPSH), leading to the earlier start of the rainy seasons and occurrence time of the precipitation annual peaks over Eastern China comparing with the observation and BCC_CSM1.1 m simulation. The improved EASM onset and northward jump of WPSH in BCC_CSM1.1 m model resulted in better simulation of precipitation seasonal transition and occurrence time of the precipitation annual peaks. However, compared to BCC_CSM1.1 model, the much more underestimated summer precipitation over most Eastern China in BCC_CSM1.1 m model is mainly due to the weakly simulated northeastward water vapor transport which is resulted from the much stronger WPSH with farther northwest location and weaker land sea thermal contrast (LSTC).

Description: The emission of mineral dust aerosols in arid and semi-arid regions is a complex process whose representation in atmospheric models remains crude, due to insufficient knowledge about the aerosol lifting process itself, the lack of global data on soil characteristics, and the impossibility for the models to resolve the fine-scale variability in the wind field that drives some of the dust events. As a result, there are large uncertainties in the total emission flux of mineral dust, its natural variability at various timescales, and the possible contribution from anthropogenic land use changes. This work aims for estimating dust emissions and reduce their uncertainty over the Sahara Desert and the Arabian Peninsula –the largest dust source region of the globe. We use a data assimilation approach to constrain dust emission fluxes at a monthly resolution for 18 sub-regions. The MODIS satellite-derived aerosol optical depth is assimilated in a regional configuration of a general circulation model coupled to an aerosol model. We describe this data assimilation system and apply it for one year, resulting in a total mineral dust emissions flux estimate of 2900 Tg year −1 over the Sahara Desert and the Arabian Peninsula for the year 2006. The analysis field of aerosol optical depth shows an improved fit relative to independent AERONET measurements as compared to the model prior field.

Description: The marine boundary layer of the northeastern U.S. is studied with focus on wind speed, atmospheric stability, and turbulent kinetic energy (TKE), the three most relevant properties in the context of offshore wind power development. Two long-term observational datasets are analyzed. The first one consists of multi-level meteorological variables measured during 2003-2011 at the offshore Cape Wind tower up to 60 m, located near the center of the Nantucket Sound. The second dataset comes from the 2013-2014 IMPOWR campaign (Improving the Modeling and Prediction of Offshore Wind Resources), in which wind and wave data were collected with new instruments on the Cape Wind platform, in addition to meteorological data measured during 19 flight missions offshore of New York, Connecticut, Rhode Island, and Massachusetts. It is found that in this region: 1) the offshore wind resource is remarkable, with monthly-average wind speeds at 60 m exceeding 7 m s -1 all year round, highest winds in winter (10.1 m s -1 ) and lowest in summer (7.1 m s -1 ), and a relatively weak diurnal modulation on average; 2) the marine boundary layer is predominantly unstable, meaning that mixing is strong, heat fluxes are positive, and the wind speed profile is often non-logarithmic (~40% of the time); and 3) the shape of the wind speed profile (log versus non-log) is an effective qualitative proxy for atmospheric stability, whereas TKE alone is not.

Description: Hydroclimatic process in the Yarlung Tsangpo River (YTR) basin, a sensitive area to climate change, is obviously changing during recent years, but there has limited understanding about it. In this study, we investigated the spatiotemporal variation of precipitation over last four decades in the basin, and the impact thereon of the changing Indian summer monsoon at inter-annual and decadal time scales. All the precipitation series have similar scaling behavior, reflecting similar climatic regime throughout the basin. However, the effect of the Indian monsoon strengthens from the downstream to upstream, causing spatial variability in the seasonal distribution of precipitation, and on this basis the YTR basin is roughly divided into three regions: east, mid and west. Both the occurrence times and magnitude of precipitation extremes, ranging 25-50 mm/day, are exhibiting downward trends over the last four decades, which bodes well for water disaster controls in the basin. The Indian summer monsoon index, as an intensity indicator for the Indian summer monsoon, shows a positive relationship with the summer precipitation in the YTR basin. Periodic variability of the Indian monsoon determines the inter-annual nonstationary fluctuations of precipitation. Especially, the weakening effect of the Indian summer monsoon has caused an obvious decrease in precipitation over the rainy season after 1998. If the Indian summer monsoon keeps weakening, the precipitation would decrease and potentially water shortage would become more severe in the basin. Effective adaptation strategy should therefore be developed proactively to handle the unfavorable water situation, which is likely to occur in the future.

Description: The light absorbing properties of water-soluble brown carbon (WS-BrC) and methanol-soluble brown carbon (MeS-BrC) were studied in PM 10 aerosols collected at the “Nepal Climate Observatory-Pyramid” (NCO-P) station (5079 m a.s.l.) during the period 2013-2014. The light absorption coefficients of WS-BrC and MeS-BrC were the highest during the pre-monsoon season and the lowest during monsoon. MeS-BrC absorbs about 2 times higher at 365 nm and about 3 times more at 550 nm compared to WS-BrC. The mass absorption cross-section (MAC) of WS-BrC measured at 365 nm is similar to that observed previously at South Asian low-altitude sites. Fractional solar radiation absorption by BrC compared to BC considering the full solar spectrum showed that WS-BrC absorbs 4 ± 1% and MeS-BrC absorbs 9 ± 2% compared to BC at NCO-P. Such ratios become 8 ± 1% (for WS-BrC respect to BC) and 17 ± 5% (for MeS-BrC respect to BC) when accounting for correction factors proposed by previous studies to convert absorption coefficients in bulk solutions into light absorption by accumulation mode aerosol particles. These results confirm the importance of BrC in contributing to light-absorbing aerosols in this region of the world. However, the BrC absorption at 550 nm appears small compared to that of BC (1-4%, or 3 – 8% with conversion factors), and it is lower compared to global model estimates constrained by AERONET observations. Finally, our study provides no clear evidence of a change in the fractional contribution of BrC with respect to BC to light absorption in the middle troposphere respect to the Indo-Gangetic plain boundary layer.

Description: Clouds in the presence of absorbing aerosols results in their apparent darkening, observed at the Top of Atmosphere (TOA), which is associated with the radiative effects of aerosol absorption. Owing to the large warming radiative effect and potential impacts on regional climate, above-cloud aerosols have recently been characterized in multiple satellite-based studies. While satellite data are particularly useful in demonstrating the radiative impact of above-cloud aerosols at the TOA, there remains uncertainties in the in-depth understanding of aerosol-cloud radiative interactions and climate effects. Furthermore, recent literature indicates large uncertainties in satellite retrievals of above-cloud Aerosol Optical Depth (AOD) and Single Scattering Albedo (SSA), which are among the most important parameters in the assessment of associated radiative effects. In this study, we analyze radiative characteristics of clouds in the presence of wildfire smoke using airborne data primarily from NASA's Cloud Absorption Radiometer, collected during the ARCTAS campaign in Canada during the 2008 summer season. We found a strong positive reflectance ( R ) gradient in the UV-VIS-NIR spectrum for clouds embedded in dense smoke, as opposed to an (expected) negative gradient for cloud-free smoke and a flat spectrum for smoke-free cloud cover. Several cases of clouds embedded in thick smoke were found, when the aircraft made circular/spiral measurements, which not only allowed the complete characterization of angular distribution of smoke scattering, but also provided the vertical distribution of smoke and clouds (within 0.5 – 5 km). Specifically, the largest darkening by smoke was found in the UV/VIS, with R 0.34μm reducing to 0.2 (or 20%), in contrast to 0.8 observed at NIR wavelengths (e.g. 1.27 µm). The observed darkening was found to be associated with large AODs (0.5 – 3.0) and moderately low SSA (0.85 – 0.93 at 0.53 µm), resulting in a significantly large instantaneous aerosol forcing efficiency of 254 ± 47 Wm -2 τ -1 . Our observations of smoke-cloud radiative interactions were found to be physically consistent with theoretical plane-parallel 1D and Monte Carlo 3D radiative transfer calculations, capturing the observed gradient across UV-VIS-NIR. Results from this study offer insights into aerosol-cloud radiative interactions, and may help in better constraining satellite-retrieval algorithms.

Description: Variations in oxygen isotope compositions (δ 18 O) provide insight into modern climate and past changes in climate and topography. In addition, in regions such as Tibet, geologic archives of isotope ratios record climate change driven by plateau uplift and therefore also provide information about the surface uplift history. A good understanding of modern day controls on δ 18 O is crucial for interpreting geologic δ 18 O in this context. We use the ECHAM5-wiso global atmospheric general circulation model to calculate δ 18 O in precipitation (δ 18 O p ) for the present-day climate. In the region of the Tibetan Plateau, spatial variations of monthly means of δ 18 O p are statistically related to spatial variations of 2 m-air temperature and precipitation rate, as well as to topography. The size and location of investigated regions are varied in our study to capture regional differences in these relationships and the processes governing the modern δ 18 O p . In addition to correlation analyses, a cross-validated stepwise multiple regression is carried out using δ 18 O p as the predictand and topography and atmospheric variables (temperature, precipitation amount) as predictors. 2 m-air temperature and topography yield the highest spatial correlation coefficients of 〉0.9 and 〈 -0.9 respectively, throughout most of the year. Particularly high correlation coefficients are calculated for the region along the Himalayan orogeny and parts of Western China. The predictors explain 〉90% of the δ 18 O p spatial variance in the same regions. 2 m-air temperature is the dominant predictor and contributes 93.6% to the total explained spatial variance on average. The results demonstrate that most of the δ 18 O p pattern on and around the Tibetan Plateau can be explained by variation in 2 m-air temperature and altitude. Correlation of the dependent predictors indicate that in low-altitude regions where topography does not determine temperature variability, the high correlation of temperature and δ 18 O p may partially be explained by variations in precipitation rates.

Description: Light-absorbing atmospheric aerosols such as carbonaceous particles influence the climate through absorbing sunlight. The mixing states of these aerosol particles affect their optical properties. This study examines the changes in the mixing states and abundance of strongly light-absorbing carbonaceous particles by using transmission electron microscopy (TEM) and single-particle soot photometer (SP2), as well as of iron-oxide particles, in Tokyo, Japan. TEM and SP2 use fundamentally different detection techniques for the same light-absorbing particles. TEM allows characterization of the morphological, chemical, and structural features of individual particles, whereas SP2 optically measures the number, size, and mixing states of black carbon (BC). A comparison of the results obtained using these two techniques indicates that the peaks of high soot (nanosphere soot (ns-soot)) concentration periods agree with those of the BC concentrations determined by SP2 and that the high Fe-bearing particle fraction periods measured by TEM agree with that of high number concentrations of iron-oxide particles measured using SP2 during the first half of the observation campaign. The results also show that the changes in the ns-soot/BC mixing states primarily correlate with the air mass sources, wind speed, precipitation, and photochemical processes. Nano-sized, aggregated, iron-oxide particles mixed with other particles were commonly observed by using TEM during the high-iron-oxide particle periods. We conclude that, although further quantitative comparison between TEM and SP2 data will be needed, the morphologically and optically defined ns-soot and BC, respectively, are essentially the same substance and that their mixing states are generally consistent across the techniques.

Description: No abstract is available for this article.

Description: The present study aims to examine the new understanding of cyclogenesis by analyzing the genesis sequence of formation of a very severe cyclonic storm Madi (6-13 December 2013) occurred over the Bay of Bengal (BoB). We have generated high resolution (18 km, 6 km, and 2 km) analysis using three-dimensional variational (3DVAR) data assimilation technique and Weather Research and Forecasting (WRF) model. The genesis sequence of Madi cyclone is analyzed using the concepts in the marsupial theory and other theories of tropical cyclone formation. Major results are as follows, the developed analysis is found useful for tracking the movement of westward moving parent disturbance from 15 days prior to the genesis; identifying developed pouch region in the Lagrangian frame of reference; understanding the evolution of the pouch and convection within the pouch region and for the study of intensification inside the pouch region. Also, large scale priming of environment concurs with the hypotheses of the marsupial theory of tropical cyclogenesis. The analysis of dynamical and thermodynamical processes within the pouch region showed gradual moistening, uplifting of moisture, diabatic heating causing buoyant convection in the vorticity rich environment followed by vortex tube stretching, development of convection, heavy precipitation, strengthening of lower level convergence and hence spinup during a day or two preceding the genesis of Madi cyclone. In general, it is concluded that intensification within pouch region during the cyclogenesis phase followed the marsupial paradigm and bottom-up mechanism.

Description: The coupled global climate model fidelity in representing upper ocean salinity including near-surface bulk salinity (SSS) is evaluated in this study, with a focus on the Pacific Ocean. The systematic biases in ocean surface evaporation (E) minus precipitation (P) and SSS are found to be fairly similar in the 20th century simulations of the Coupled Model Intercomparison Phase 3 (CMIP3) and Phase 5 (CMIP5) relative to the observations. One of the potential causes of the CMIP model biases is the missing representation of the radiative effects of precipitating hydrometeors (i.e., snow) in most CMIP models. To examine the radiative effect of cloud snow on SSS, sensitivity experiments with and without such effect are conducted by the NCAR coupled Community Earth System Model (CESM). This study investigates the difference in SSS between sensitivity experiments and its relationship with atmospheric circulation, E-P and air-sea heat fluxes. It is found that the exclusion of the cloud snow radiative effect in CESM produces weaker Pacific trade winds, resulting in enhanced precipitation, reduced evaporation, and a reduction of the upper-ocean salinity in the tropical and sub-tropical Pacific. The latter results in an improved comparison with climatological upper-ocean bulk salinity. The introduction of cloud snow also altered the budget terms that maintain the time-mean salinity in the mixed layer.

Description: The El Niño–Southern Oscillation (ENSO) has significant effects on the extratropical stratosphere. This study explores the nonlinearity and the asymmetry of these influences by distinguishing the different effects of four types of ENSO: “moderate El Niño”, “strong El Niño”, “moderate La Niña”, and “strong La Niña”. It is revealed that the moderate El Niño and the strong La Niña are much more efficient than the strong El Niño and the moderate La Niña, respectively, in modulating the northern winter stratospheric variability, resulting in significant nonlinearity and asymmetry. The tropical rainfall anomalies induced by a moderate El Niño or a strong La Niña are centered over the central equatorial Pacific region near the dateline, while the convection responses to a strong El Niño or a moderate La Niña are centered farther eastward. Accordingly, the anomalous Pacific–North America wave train pattern is modulated by ENSO in a nonlinear and asymmetric way, which leads the large nonlinear and asymmetric components of the vertical Eliassen-Palm (E–P) flux responses to ENSO. The increase of planetary wave activity in the extratropical stratosphere in moderate El Niño winters is thus greater than in strong El Niño winters, whereas a strong La Niña gives a larger decrease in propagation than a moderate La Niña. The relatively strong (weak) E–P flux responses to moderate (strong) El Niño and strong (moderate) La Niña explain the remarkable nonlinearity and asymmetry in the response of the extratropical stratosphere to ENSO.

Description: Microphysical characteristics of pre-monsoon and monsoon deep cumuli over India observed by an instrumented aircraft are contrasted focusing on influences of environmental conditions and entrainment-mixing processes. Differences in the lower-tropospheric temperature and moisture profiles lead to contrasting undiluted cloud buoyancy profiles around the cloud base, larger in the pre-monsoon case. It is argued that this affects the variation of the mean and maximum cloud droplet number concentrations and the droplet radius within the lowest several hundred meters above the cloud base. The conserved-variable thermodynamic diagram analysis suggests that entrained parcels originate from levels close to the observational level. Mixing processes and their impact on the droplet size distribution (DSD) are investigated contrasting 1 Hz and 10 Hz observations. Inhomogeneous-type mixing, likely because of unresolved small-scale structures associated with active turbulent stirring, is noted at cloud edge volumes where dilution is significant and DSDs shift towards smaller sizes with reduced droplet number concentrations due to complete evaporation of smaller droplets and partial evaporation of larger droplets. DSDs within cloud core volumes suggest that the largest droplets are formed in the least diluted volumes where raindrops can form at higher levels; no super-adiabatic droplet growth is observed. The typical diluted parcel size is approximately 100–200 m for cloud edge volumes, and it is much smaller, 10–20 m, for cloud core volumes. Time scale analysis indicates the possibility of inhomogeneous type mixing within the diluted cloud edge volumes at spatial scales of a 100 m or more.

Description: Soil moisture is at the heart of many processes connected to water cycle, climate, ecosystem and societal conditions. This paper investigates the ability of a relatively simple analytical soil-moisture model to reproduce temporal variability dynamics in long-term data series for: (i) remotely sensed large-scale water storage change in twenty-five large catchments around the world, and (ii) measured soil water content and groundwater level in individual stations within ten smaller catchments across the United States. The model-data comparison for large-scale water storage change (i) shows good model ability to reproduce the observed temporal variability around long-term average conditions in most of the large study catchments. Also the model comparison with locally measured data for soil water content and groundwater level in the smaller U.S. catchments (ii) shows good representation of relative seasonal and longer-term fluctuations and their timings and frequencies. Overall, the model results tend to underestimate rather than exaggerate the range of temporal soil moisture fluctuations and storage changes. The model synthesis of large-scale hydro-climatic data is based on fundamental catchment-scale water balance and is as such useful for identifying flux imbalance biases in the hydro-climatic data series that are used as model inputs.

Description: Thinning of Arctic sea ice gives rise to ice fracturing and leads (areas of open water surrounded by sea ice) that are a potential source of sea salt aerosol. Atmospheric particle inorganic ion concentrations, local sea ice conditions, and meteorology at Barrow, AK from 2006-2009 were combined to investigate the dependence of submicron (aerodynamic diameter 〈 1 µm) and supermicron (aerodynamic diameter 1-10 µm) sea salt mass concentrations on sea ice coverage and wind speed. Consistent with a wind-dependent source, supermicron sea salt mass concentrations increased in the presence of nearby leads and wind speeds greater than 4 m s -1 . Increased supermicron and submicron sea salt chloride depletion was observed for periods of low winds or a lack of nearby open water, consistent with transported sea salt influence. Sea salt aerosol produced from leads has the potential to alter cloud formation, as well as the chemical composition of the Arctic atmosphere and snowpack.

Description: Long-term simulations from the Community Earth System Model with the Whole Atmosphere Community Climate Model (CESM-WACCM) as its atmospheric component are used to investigate the asymmetry and the nonlinearity of the influences of El Niño–Southern Oscillation (ENSO) on the northern winter stratosphere. As in Part I of this study, four different types of ENSO are considered. The composite CESM-WACCM results first confirm the conclusions drawn from the observations, that the stratospheric polar jet responses to “moderate El Niño” and “strong La Niña” are stronger than those to “strong El Niño” and “moderate La Niña”. In association with the ENSO sea surface temperature (SST) patterns that are reproduced well in the model, the tropical rainfall response centers exhibit an asymmetric east–west shift between El Niño and La Niña, which directly leads to the nonlinear and asymmetric PNA responses in the extratropics. Accordingly, the strengthening (weakening) planetary wave response in the stratosphere during warm (cold) ENSO also exhibits nonlinear and asymmetric features. When the ENSO SST forcing is prescribed to be linear and symmetric in WACCM, the nonlinearity and asymmetry of the stratospheric responses to moderate ENSO reveal the dominant role of the inherent properties of the atmosphere. However, the absence of asymmetry and nonlinearity in the stratospheric responses to strong ENSO in our sensitivity experiments indicates that the asymmetry in SST forcing between strong El Niño and La Niña still plays an important role in the asymmetric and nonlinear influences of ENSO on the extratropics.

Description: Shortwave Infrared (SWIR) imaging spectroscopy enables accurate remote mapping of cloud thermodynamic phase at high spatial resolution. We describe a measurement strategy to exploit signatures of liquid and ice absorption in cloud top apparent reflectance spectra from 1.4-1.8  μ m. This signal is generally insensitive to confounding factors such as solar angles, view angles, and surface albedo. We first evaluate the approach in simulation, and then apply it to airborne data acquired in the Calwater-2 / ACAPEX campaign of Winter 2015. Here, NASA's “Classic” Airborne Visible Infrared Imaging Spectrometer (AVIRIS-C) remotely observed diverse cloud formations while the US Department of Energy ARM Aerial Facility (AAF) G-1 aircraft measured cloud integral and microphysical properties in situ . The coincident measurements demonstrate good separation of the thermodynamic phases for relatively homogeneous clouds.

Description: Surface based temperature inversions (SBIs) occur frequently over Antarctica and play an important role in climate and weather. Antarctic SBIs are examined during Austral spring, 2010 using measurements from dropsondes, ERA-Interim Atmospheric Reanalysis Model, and the recently released version 6 of the Infrared Atmospheric Sounding Interferometer (IASI) level 2 product. A SBI detection algorithm is applied to temperature profiles from these datasets. The results will be used to determine if satellite and reanalysis products can accurately characterize SBIs and if so, then they may be used to study SBIs outside of the spring 2010 study period. From the dropsonde data, SBIs occurred in 20% of profiles over sea ice and 54% of profiles over land. IASI and ERA-Interim surface air temperatures are found to be significantly warmer than dropsonde observations at high plateau regions, while IASI surface air temperature is colder over sea ice. IASI and ERA-Interim have a cold bias at nearly all levels above the surface when compared to the dropsonde. SBIs are characterized by their frequency, depth, and intensity. It is found that SBIs are more prevalent, deeper, and more intense over the continent than over sea ice, especially at higher surface elevations. Using IASI and ERA-Interim data the detection algorithm has a high probability of detection of SBIs but is found to severely overestimate the depth and underestimate the intensity for both data sets. These over- and underestimations are primarily due to the existence of extremely shallow inversion layers that neither satellite nor reanalysis products can resolve.

Description: Recent warming of the Antarctic Peninsula during austral autumn, winter, and spring has been linked to sea surface temperature (SST) trends in the tropical Pacific and tropical Atlantic, while warming of the northeast Peninsula during summer has been linked to a strengthening of westerly winds traversing the Peninsula associated with a positive trend in the Southern Annular Mode (SAM). Here we demonstrate that circulation changes associated with the SAM dominate interannual temperature variability across the entire Antarctic Peninsula during both summer and autumn, while relationships with tropical Pacific SST variability associated with the El Niño-Southern Oscillation (ENSO) are strongest and statistically significant primarily during winter and spring only. We find the ENSO-Peninsula temperature relationship during autumn to be weak on interannual timescales, and regional circulation anomalies associated with the SAM more important for interannual temperature variability across the Peninsula during autumn. Consistent with previous studies, western Peninsula temperatures during autumn, winter, and spring are closely tied to changes in the Amundsen Sea Low (ASL) and associated meridional wind anomalies. The interannual variability of ASL depth is most strongly correlated with the SAM index during autumn, while the ENSO relationship is strongest during winter and spring. Investigation of western and northeast Peninsula temperatures separately reveals that interannual variability of northeast Peninsula temperatures is primarily sensitive to zonal wind anomalies crossing the Peninsula and resultant lee-side adiabatic warming rather than to meridional wind anomalies, which is closely tied to variability in the zonal portion of the SAM pattern.

Description: We use a 0-D photochemical box model and a 3-D global chemistry-climate model, combined with observations from the NOAA Southeast Nexus (SENEX) aircraft campaign, to understand the sources and sinks of glyoxal over the Southeast United States. Box model simulations suggest a large difference in glyoxal production among three isoprene oxidation mechanisms (AM3ST, AM3B, and MCM v3.3.1). These mechanisms are then implemented into a 3-D global chemistry-climate model. Comparison with field observations shows that the average vertical profile of glyoxal is best reproduced by AM3ST with an effective reactive uptake coefficient γ glyx of 2 × 10 -3 , and AM3B without heterogeneous loss of glyoxal. The two mechanisms lead to 0-0.8 µg m -3 secondary organic aerosol (SOA) from glyoxal in the boundary layer of the Southeast U.S. in summer. We consider this to be the lower limit for the contribution of glyoxal to SOA, as other sources of glyoxal other than isoprene are not included in our model. In addition, we find that AM3B shows better agreement on both formaldehyde and the correlation between glyoxal and formaldehyde ( R GF  = [GLYX]/[HCHO]), resulting from the suppression of δ-isoprene peroxy radicals (δ-ISOPO 2 ). We also find that MCM v3.3.1 may underestimate glyoxal production from isoprene oxidation, in part due to an underestimated yield from the reaction of IEPOX peroxy radicals (IEPOXOO) with HO 2 . Our work highlights that the gas-phase production of glyoxal represents a large uncertainty in quantifying its contribution to SOA.

Description: Based on the results from eleven flux sites during the third Tibetan Plateau (TP) Experiment (TIPEX III), land surface parameters and the turbulence characteristics of the atmospheric surface layer over the TP and surrounding region are analyzed. Monin-Obukhov similarity theory has been used to calculate the aerodynamic roughness length z 0m and the excess resistance to heat transfer kB − 1  = ln( z 0 m / z 0 h ), and the factors that cause variations of z 0m and kB − 1 are investigated. The main sdrivers for the diurnal variations of surface albedo( α ) at different sites are solar elevation, solar radiation, and soil moisture. The eddy correlation method is utilized to inversely calculate bulk transfer coefficients for momentum ( C D ) and heat ( C H ) at different sites. The relationships between C D and C H , and the wind speed at 10 m follow a power law for unstable stratification. For stable stratification, both C D and C H increase with increasing wind speed when wind speed is less than 5 m/s. Diurnal variations of turbulent fluxes are compared at different sites, and the relationships between turbulent fluxes and other variables are analyzed. Wind speed variance normalized by the friction velocity ( σ u / u * ,  σ v / u * ,  σ w / u * ) for neutral stratification ( C u1 , C v1 , C w1 ), and temperature and humidity variance normalized by a temperature and humidity scale ( σ T / T * ,  σ q / q * ) under free convection ( z/L  〈 -0.1) ( C T , C q ) are fitted with similarity relations. The differences in similarity constants ( C u1 , C v1 , C w1 , C T , C q ) at different sites are discussed. For stable stratification, cases are divided into weakly stable conditions and intermittent turbulence, and the critical values for these two states are determined. Shear and buoyancy terms in the turbulence kinetic energy (TKE) equation for different stratifications are analyzed.

Description: Contrail cirrus is the largest known component contributing to the radiative forcing associated with aviation. Despite major advances simulating contrail cirrus, their microphysical and optical properties and the associated radiative forcing remain largely uncertain. We use a contrail cirrus parameterization in a global climate model which was extended to include a microphysical two-moment scheme. This allows a more realistic representation of microphysical processes, such as deposition and sedimentation, and therefore of the microphysical and optical properties of contrail cirrus. The simulated contrail microphysical and optical properties agree well with in situ and satellite observations. As compared to estimates using an older version of the contrail cirrus scheme, the optical depth of contrail cirrus is significantly higher, particularly in regions with high air traffic density, due to high ice crystal number concentrations on the main flight routes. Nevertheless, the estimated radiative forcing for the year 2002 supports our earlier results. The global radiative forcing of contrail cirrus for the year 2006 is estimated to be 56mW/m 2 . A large uncertainty of the radiative forcing estimate appears to be connected with the, on average, very small ice crystal radii simulated in the main air traffic areas, which make the application of a radiative transfer parameterization based on geometric optics questionable.

Description: The Lake Siling Co is currently the largest endorheic lake in Tibet and the lake surface area has expanded by about 40% since the 1970s, with a remarkable acceleration after 1999. In this study, a hydrologic modeling framework was established by linking the Variable Infiltration Capacity (VIC) land surface hydrologic model with the degree-day glacier-melt model over the Lake Siling Co basin, with the aim to quantify the contribution of each runoff component to changes in the lake storage. We found that glacier melt contributed to less than 10% of the total water input to the lake during 1979–2013, while precipitation-induced runoff in non-glacierized area was responsible for about 67–75%. The mean annual water input to the lake increased by 2.15 × 10 9 m 3 yr −1 in 2000–2013 relative to that in 1979–1999. The amount of precipitation over the lake surface, precipitation-induced runoff, and glacier-melt runoff accounted for 13%, 82% and 5% of this total increase, respectively, suggesting that the substantial expansion of Siling Co in the 2000s was mostly due to the increase in precipitation-induced runoff. When modeling lake level changes during 1979–2013, we found that the water level rose by 14.1 m when glacier melt was included and only 10.5 m, a reduction of about 1/4, when glacier melt was removed. It is concluded that glacier melt played an important role in controlling the water level of Siling Co, although it only contributed less than 10% of water input to the lake during 1979–2013.

Description: High elevations are thought to be warming more rapidly than lower elevations, but there is a lack of air temperature observations in high mountains. This study compares instantaneous values of land surface temperature (1030/2230 and 0130/1330 local solar time) as measured by MODIS MOD11A2/MYD11A2 at 1 km resolution from the TERRA and AQUA platforms respectively with equivalent screen level air temperatures (in the same pixel). We use a transect of 22 in situ weather stations across Kilimanjaro ranging in elevation from 990 to 5803 m, one of the biggest elevational ranges in the world. There are substantial differences between LST and T air , sometimes up to 20˚C. During the day/night LST tends to be higher/lower than T air . LST-T air differences (ΔT) show large variance, particularly during the daytime, and tend to increase with elevation, particularly on the NE slope which faces the morning sun. Differences are larger in the dry seasons (JF and JJAS), and reduce in cloudy seasons. Healthier vegetation (as measured by NDVI) and increased humidity lead to reduced daytime surface heating above air temperature and lower ΔT, but these relationships weaken with elevation. At high elevations transient snow cover cools LST more than T air . The predictability of ΔT therefore reduces. It will therefore be challenging to use satellite data at high elevations as a proxy for in situ air temperatures in climate change assessments, especially for daytime T max. ΔT is smaller and more consistent at night, so it will be easier to use LST to monitor changes in T min.

Description: Atmospheric observations of greenhouse gases provide essential information on sources and sinks of these key atmospheric constituents. To quantify fluxes from atmospheric observations, representation of transport – especially vertical mixing – is a necessity and often a source of error. We report on remotely sensed profiles of vertical aerosol distribution taken over a two-year period in Pasadena, California. Using an automated analysis system, we estimate daytime mixing layer depth, achieving high confidence in the afternoon maximum on 51% of days with profiles from a Sigma Space Mini Micropulse LiDAR (MiniMPL) and on 36% of days with a Vaisala CL51 ceilometer. We note that considering ceilometer data on a logarithmic scale, a standard method, introduces an offset in mixing height retrievals. The mean afternoon maximum mixing height is 770 m AGL in summer and 670 m in winter, with significant day-to-day variance (within-season σ = 220m≈30 % ). Taking advantage of the MiniMPL's portability, we demonstrate the feasibility of measuring the detailed horizontal structure of the mixing layer by automobile. We compare our observations to PBL heights from sonde launches, NARR reanalysis, and a custom WRF model developed for GHG monitoring in Los Angeles. NARR and WRF PBL heights at Pasadena are both systematically higher than measured, NARR by 2.5 times; these biases will cause proportional errors in GHG flux estimates using modeled transport. We discuss how sustained lidar observations can be used to reduce flux inversion error by selecting suitable analysis periods, calibrating models, or characterizing bias for correction in post-processing.

Description: The analysis of high-energy background radiation (0.1-2MeV) enhancements during eight winter thunderstorms and five summer storms in the Ebro delta region in the northeast of Spain is presented. For the first time, high-energy radiation counts, precipitation, radar reflectivity and very high frequency lightning detections to infer charge regions altitude have been analysed in order to find out what produces the measured background radiation increments associated with storms. The good agreement between radar reflectivity and precipitation with increases in background radiation counts coupled with the spectrum analysis comparing rain/no rain periods suggests that radon-ion daughters play a major role in the radiation increments reported. No evidence has been found supporting that measured background radiation enhancements can be produced by storm electric fields. Finally, a single case of a high energy radiation increase was prior to a cloud-to-ground lightning stroke which reinforces the theory of a lower positive charge layer to exist is important for the production of Terrestrial Ground Enhancements (TGEs).

Description: During 1961-2012, the regional average annual potential evapotranspiration (PET) of Southwest China (SWC) and the four subregions (named as SR1, SR2, SR3 and SR4) showed different decreases (excluding SR3); while the break-points analysis suggested that PET changes (i.e., sign and magnitude) have shifted. Based on a group of sensitivity experiments with Penman-Monteith equation and a new separating method, the contributions of each climate factor alone (i.e., net radiation, Rn; mean temperature, Tave; wind speed, Wnd; and vapor pressure deficit, Vpd) to PET changes were calculated. Results showed that declined Wnd in SR1, reduced Rn in SR2, SR4 and SWC, and increased Vpd in SR3 were responsible for the PET changes during 1961-2012. However, the determinant factor for each subregion and SWC varied in different segmented periods, which were identified using the break-point analysis. The impacts of PET shifts on SWC dryness/wetness [reflected by the 3-month Standardized Precipitation-Evapotranspiration index, (SPEI-3)] during 1961-2012 were then quantified. Briefly, SPEI-3 changes in SR3, SR4 and SWC had the determinant factor of PET in the first one or two period(s), and precipitation in the last period; while they were attributed to PET (precipitation) in SR1 (SR2) for each segmented period. It is found that PET and precipitation had comparable contributions to the variations in SWC dryness/wetness. Our findings have suggested that more attentions should be paid to the impacts of PET changes and shifts in future studies of dryness/wetness or drought.

Description: The 20 th century climate simulations from the Coupled Model Intercomparison Project Phase 3 (CMIP3) and Phase 5 (CMIP5) are compared to assess the models' ability to capture observed near surface air temperature trends at global, continental, and regional scales. We computed trends using a non-parametric method and considering long-term persistence in the time series. The role of internal variability is examined using large ensemble climate simulations from the National Center for Atmospheric Research (NCAR) model CESM. We computed temperature trends for three periods: (1) the 20 th century, (2) the second half of the 20 th century, and (3) the recent hiatus period to contrast the roles of external forcing and internal variability at various spatial and temporal scales. Both CMIP ensembles show statistically significant warming at global and continental scales during the 20 th century. We found a small but statistically significant difference between CMIP3 (0.57 ± 0.07 °C/century) and CMIP5 (0.47 ± 0.06 °C/century) 20 th century temperature trends, with the CMIP3 estimate being closer to the observations. The spatial structure of long-term temperature trends, and top-of-the atmosphere net radiation trends, suggests that differences in model parameterizations and feedback processes that lead to a smaller net radiative forcing is likely contributing to the differences between CMIP3 and CMIP5. The estimate of internal variability based on the CESM large ensemble spans 24% of the uncertainty in CMIP5 for the 20 th century temperature trends, and 76% for the recent hiatus period, both at global scales, and 43% and almost 100% during the corresponding time periods at regional scales.

Description: The role of turbulent mixing in formation of low horizontal variability of effective radius near the top of non-drizzling stratocumulus clouds is investigated in simulations of clouds observed during the DYCOMS-II field experiment. The clouds are simulated using a spectral bin microphysics Lagrangian-Eulerian model (LEM) consisting of ~2000 adjacent parcels moving in a turbulence-like field with observed correlation properties. The parcels interact through drop sedimentation and turbulent mixing. It was found that the effective radius variability in the horizontal direction near cloud top does not exceed ~10% of the averaged value. Three different types of cloud parcels are revealed to be differently influenced by mixing: ascending slightly diluted parcels, cloudy parcels experiencing intense mixing with parcels from inversion, and initially dry parcels. The evolution of droplet size distributions (DSD) in parcels belonging to these types is investigated. It is shown that in parcels of the first two types the values of effective radii do not change or change only slightly remaining close to the adiabatic value. In initially droplet-free parcels effective radius rapidly reaches a value close to the adiabatic value, while liquid water content remains low. Therefore, turbulent mixing leads to establishing vertical profiles of effective radius which are close to the adiabatic profile.

Description: During the winters of 2013-2014 and 2014-2015, anomalously warm temperatures in western North America and anomalously cool temperatures in eastern North America resulted in substantial human and environmental impacts. Motivated by the impacts of these concurrent temperature extremes and the intrinsic atmospheric linkage between weather conditions in the western and eastern United States, we investigate the occurrence of concurrent “warm-West/cool-East” surface temperature anomalies, which we call the “North American Winter Temperature Dipole”. We find that, historically, warm-West/cool-East dipole conditions have been associated with anomalous mid-tropospheric ridging over western North America and downstream troughing over eastern North America. We also find that the occurrence and severity of “warm-West/cool-East” events has increased significantly between 1980 and 2015, driven largely by an increase in the frequency with which high-amplitude “ridge-trough” wave patterns result in simultaneous severe temperature conditions in both the West and East. Using a large single-model ensemble of climate simulations, we show that the observed positive trend in the “warm-West/cool-East” events is attributable to historical anthropogenic emissions including greenhouse gases, but that the co-occurrence of extreme western warmth and eastern cold will likely decrease in the future as winter temperatures warm dramatically across the continent, thereby reducing the occurrence of severely cold conditions in the East. Although our analysis is focused on one particular region, our analysis framework is generally transferable to the physical conditions shaping different types of extreme events around the globe.

Description: A novel dynamically-based index that reflects the strength of the regional potential vorticity (PV) intrusion on the 300 K isentropic surface is proposed as a reliable measure of East Asian winter monsoon (EAWM) intensity. The index captures essential aspects of the EAWM, including its climatic influences on East Asia, its continuous weakening trend since the 1980s, and its close relationships with the Siberian high, Arctic Oscillation, and El Niño. The use of a potential vorticity framework enables the definition of a new metric called Continuous PV Intrusion Duration (CPVID), which can be used to monitor and explain wintertime weather extremes like the extreme snowfall event that occurred in South China during January 2008. The CPVID of March is comparable to that of December, indicating that data from this month should be included in estimates of the strength of the EAWM.

Description: To optimize flood management, it is crucial to determine whether rain will fall within a river basin. This requires very fine precision in prediction of rainfall areas. Cloud data assimilation has great potential to improve the prediction of precipitation area because it can directly obtain information on locations of rain systems. Clouds can be observed globally by satellite-based microwave remote sensing. Microwave observation also includes information of latent heat and water vapor associated with cloud amount, which enables the assimilation of not only cloud itself but also the cloud-affected atmosphere. However, it is difficult to observe clouds over land using satellite microwave remote sensing, because their emissivity is much lower than that of the land surface. To overcome this challenge, we need appropriate representation of heterogeneous land emissivity. We developed a coupled atmosphere and land data assimilation system with the Weather Research and Forecasting Model (CALDAS-WRF), which can assimilate soil moisture, vertically integrated cloud water content over land, and heat and moisture within clouds simultaneously. We applied this system to heavy rain events in Japan. Results show that the system effectively assimilated cloud signals and produced very accurate cloud and precipitation distributions. The system also accurately formed a consistent atmospheric field around the cloud. Precipitation intensity was also substantially improved by appropriately representing the local atmospheric field. Furthermore, combination of the method and operationally analyzed dynamical and moisture fields improved prediction of precipitation duration. The results demonstrate the method's promise in dramatically improving predictions of heavy rain and consequent flooding.

Description: The increase in cloud optical depth with warming at middle and high latitudes is a robust cloud feedback response found across all climate models. This study builds on results that suggest the optical depth response to temperature is timescale invariant for low-level clouds. The timescale invariance allows one to use satellite observations to constrain the models' optical depth feedbacks. Three passive-sensor satellite retrievals are compared against simulations from eight models from the Atmosphere Model Intercomparison Project (AMIP) of the 5th Coupled Model Intercomparison Project (CMIP5). This study confirms that the low-cloud optical depth response is timescale invariant in the AMIP simulations, generally at latitudes higher than 40°. Compared to satellite estimates, most models overestimate the increase in optical depth with warming at the monthly and interannual timescales. Many models also do not capture the increase in optical depth with estimated inversion strength that is found in all three satellite observations and in previous studies. The discrepancy between models and satellites exists in both hemispheres and in most months of the year. A simple replacement of the models' optical depth sensitivities with the satellites' sensitivities reduces the negative shortwave cloud feedback by at least 50 % in the 40° – 70°S latitude band and by at least 65 % in the 40° – 70°N latitude band. Based on this analysis of satellite observations, we conclude that the low-cloud optical depth feedback at middle and high latitudes is likely too negative in climate models.

Description: To examine the impact of an interactive ocean on numerical weather prediction (NWP), numerical simulations of a heavy snowfall are performed using a coupled atmosphere–ocean model. Results indicate that upper ocean conditions, such as the spatiotemporal variability of sea surface temperature (SST) and currents, have a significant impact on the heavy snowfall. SST condition, acting as source of energy for the formation of heavy snowfall, regulates intensity of heat and moisture fluxes and consequent convection. When an interactive ocean is included, mesoscale variations in SST in coastal regions, where satellite observations would be inaccurate, are successfully captured, and intensity and location of heavy snowfall are improved. These results suggest that coupled air–sea interaction is an important physical mechanism in the intensity and structure of extreme weather events and, thus, that the inclusion of an interactive ocean in NWP model could improve weather prediction, particularly for localized severe weather.

Description: To equitably compare the spatial pattern of ice microphysical processes produced by three microphysical parameterizations with each other, observations, and theory, simulations of tropical oceanic mesoscale convective systems (MCSs) in the Weather Research and Forecasting (WRF) model were forced to develop the same mesoscale circulations as observations by assimilating radial velocity data from a Doppler radar.. The same general layering of microphysical processes was found in observations and simulations with deposition anywhere above the 0 °C level, aggregation at and above the 0 °C level, melting at and below the 0 °C level, and riming near the 0 °C level. Thus, this study is consistent with the layered ice microphysical pattern portrayed in previous conceptual models and indicated by dual-polarization radar data. Spatial variability of riming in the simulations suggest that riming in the midlevel inflow is related to convective-scale vertical velocity perturbations. Finally, this study sheds light on limitations of current generally available bulk microphysical parameterizations. In each parameterization, the layers in which aggregation and riming took place were generally too thick and the frequency of riming was generally too high compared to the observations and theory. Additionally, none of the parameterizations produced similar details in every microphysical spatial pattern. Discrepancies in the patterns of microphysical processes between parameterizations likely factor into creating substantial differences in model reflectivity patterns. It is concluded that improved parameterizations of ice-phase microphysics will be essential to obtain reliable, consistent model simulations of tropical oceanic MCSs.

Description: The composite effect of intraseasonal sea surface temperature (SST) variability on the Madden–Julian Oscillation (MJO) is studied in the context of the column integrated moist static energy (〈 m 〉) budget using data from the European Centre for Medium-Range Weather Forecasts Interim Reanalysis (ERA-I). SST fluctuations influence the Δ q and Δ T parts of the bulk surface latent and sensible heat flux calculations, respectively, each of which influence column 〈 m 〉. Reynolds decomposition of latent and sensible heat fluxes ( L H and S H ) reveal that the thermodynamic perturbations (e.g.,  for L H ) modestly offset the equatorial wind-driven perturbations ( ) and 〈 m 〉, but strongly offset the subtropical  and 〈 m 〉. Column moistening east of MJO convection is opposed by  and supported by . Impacts of intraseasonal SST fluctuations are analyzed by recomputing surface flux component terms using 61-day running-mean SST. Differences between “full SST” and “smoothed SST” projections onto 〈 m 〉 and its tendency ( ∂ 〈 m 〉/ ∂ t ) yield the “SST effect” on the MJO 〈 m 〉 budget. Particularly in the Indian Ocean, intraseasonal SST fluctuations maintain equatorial 〈 m 〉 anomalies at a rate of 1%–2% day −1 , and damp subtropical 〈 m 〉 anomalies at a similar rate. Vertical advection (−〈 ω ∂ m / ∂ p 〉) exports 10%–20% of 〈 m 〉 day −1 , implying that the SST modulation of surface fluxes offsets roughly 10% of equatorial 〈 m 〉 export and amplifies by 10% the subtropical 〈 m 〉 export by −〈 ω ∂ m / ∂ p 〉. SST fluctuations support MJO propagation by encouraging on-equator convection and the circulation anomalies that drive MJO propagation, and by contributing up to 10% of ∂ 〈 m 〉/ ∂ t across the Warm Pool.

Description: This paper presents a detailed comparison between AIRS and MODIS measurements over the period 2003-2013 and also between MODIS and IASI for the years 2007-2014. For this study AIRS and IASI high spectral resolution data are degraded to MODIS broadband spectral resolution and MODIS fields of view are averaged within the AIRS and IASI footprints. Using spatially uniform scenes, the brightness temperature differences (ΔBT) between MODIS and AIRS are analyzed as a function of scene temperature, scan angle and solar zenith angle. In general, the measurements of the two sensors are in good agreement (ΔBT less than ±0.2K) with little or no dependence on the scene temperature. A small dependence is found for the scan angle, where ΔBT varies off-nadir up to about ±0.4K; dependence on the solar zenith angle is also observed, with ΔBT varying up to ±0.5K. Finally, the variation of ΔBT over time is stable with BT trending less than 0.02K/yr, with exception of ΔBT for MODIS bands 33 and 35 in the 2011-2013 timeframe. This behavior, which is also identified in MODIS/IASI comparisons, correlates to adjustments in that timeframe of the MODIS non-linear calibration coefficients.

Description: Accurate information about aerosol vertical distribution is needed to reduce uncertainties in aerosol radiative forcing and its effect on atmospheric dynamics. The present study deals with synergistic analyses of aerosol vertical distribution and aerosol optical depth (AOD) with meteorological variables using multi-satellite and -ground based remote sensors over Kanpur in central Indo-Gangetic Plains (IGP). Micro pulse lidar network (MPLNET)-derived aerosol vertical extinction ( σ ) profiles are analysed to quantify the inter-annual and daytime variations during monsoon onset period (May - June) for 2009 - 2011. The mean aerosol profile is broadly categorized into two layers viz. a surface layer (SL) extending up to 1.5 km (where σ decreased exponentially with height) and an elevated aerosol layer (EAL) extending between 1.5 - 5.5 km. The increase in total columnar aerosol loading is associated with relatively higher increase in contribution from EAL loading than that from SL. The mean contributions of EALs are about 60 %, 51 % and 50 % to total columnar AOD during 2009, 2010 and 2011, respectively. We observe distinct parabolic EALs during early morning and late evening, but uniformly mixed EALs during midday. The inter-annual and daytime variations of EALs are mainly influenced by long range transport and convective capacity of the local emissions, respectively. Radiative flux analysis shows that clear sky incoming solar radiation at surface is reduced with increase in AOD, which indicates significant cooling at surface. Collocated analysis of atmospheric temperature and aerosol loading reveals that increase in AOD not only resulted in surface dimming but also reduced the temperature (∼2-3 ∘ C) of lower troposphere (below 3 km altitude). Radiative transfer simulations indicate that the reduction of incoming solar radiation at surface is mainly due to increased absorption by EALs (with increase in total AOD). The observed cooling in lower troposphere in high aerosol loading scenario could be understood as a dynamical feedback of EAL induced stratification of lower troposphere. Further, the observed radiative effect of EALs increases the stability of the lower troposphere, which could modulate the large scale atmospheric dynamics during monsoon onset period. These findings encourage follow up studies on the implication of EALs to the Indian summer monsoon dynamics using numerical models.

Description: The shapes and magnitudes of latent heating profiles have been shown to be different within the convective and stratiform regions of mesoscale convective systems (MCSs). Properly representing these distinctions has significant implications for the atmospheric responses to latent heating on various scales. This study details (1) the microphysical process contributions to latent heating profiles within MCS convective, stratiform, and anvil regions, and (2) the time evolution of these profiles throughout the MCS lifetime, using cloud-resolving model simulations. Simulations of two MCS events that occurred during the Midlatitude Continental Convective Clouds Experiment (MC3E) are conducted. Several features of the simulated MCSs are compared to a suite of observations obtained during the MC3E field campaign, and it is concluded that the simulations reasonably reproduce the MCS events. The simulations show that condensation and deposition are the primary contributors to MCS latent warming, as compared to riming and nucleation processes. In terms of MCS latent cooling, sublimation, melting, and evaporation all play significant roles. It is evident that throughout the MCS lifecycle, convective regions demonstrate an approximately linear decrease in the magnitudes of latent heating rates, while latent heating within stratiform regions is associated with transitions between MCS flow regimes. Such information regarding the temporal evolution of latent heating within convective and stratiform MCS regions could be useful in developing parameterizations representing convective organization.

Description: The intraseasonal variability of gravity waves (GWs) in the austral summer middle stratosphere was examined using dedicated high-resolution temperature retrieval from the Atmospheric Infrared Sounder　data. Composite maps were made of stratospheric GW temperature variances, large-scale zonal winds around the tropopause, and precipitation based on the real-time multivariate Madden-Julian Oscillation (MJO) index. Regional distributions of these quantities are synchronized with the MJO: The GW variances are larger for stronger precipitation, and for more strongly westward wind around the tropopause at a given precipitation. These results suggest that the GWs observed by AIRS in the stratosphere originate from convection. Moreover, it is shown that the zonal wind around the tropopause likely controls the GW propagation into the stratosphere by a critical level filtering mechanism and/or the GW generation by an obstacle source effect. This means that the MJO can modulate the middle atmospheric circulation by regulating the GWs in two ways, namely, generation and propagation.

Description: Most lakes in the interior Tibetan Plateau have expanded rapidly since the late 1990s. Because of a lack of observations, lake water balances and their changes are far from well understood. Evaporation is a component of the lake water balance, and this study quantifies its magnitude, decadal change, and its contribution to the water balance changes in Lake Nam Co, one of the largest lakes on the Tibetan Plateau (with an area of approximately 2000 km 2 and a mean depth of approximately 40 m). The lake temperature and the evaporation are simulated by the Flake model. The simulation results are validated against observed lake temperature profile from 2013 and MODIS lake surface temperature data from 2000-2014. The simulated latent heat flux and sensible heat flux are validated against Bowen ratio-derived estimates for 2013. Based on the validated simulation results, the long-term mean annual evaporation is approximately 832 ± 69 mm, and this value is much less than the potential evaporation estimated using the Penman-Monteith equation. The annual evaporation from 1980-2014 displays a complex decadal oscillation, mainly due to the changes in energy-related terms (air temperature and radiation). The mean lake evaporation since the late 1990s is greater than previous periods; thus, this change in evaporation has suppressed the recent expansion of Nam Co.

Description: We analyze daily precipitation extremes from simulations of a polar-optimized version of the Weather Research and Forecasting (WRF) model. Simulations cover 19 years and use the Regional Arctic System Model (RASM) domain. We focus on Alaska because of its proximity to the Pacific and Arctic oceans; both provide large moisture fetch inland. Alaska's topography also has important impacts on orographically-forced precipitation. We use Self-Organizing Maps (SOMs) to understand circulation characteristics conducive for extreme precipitation events. The SOM algorithm employs an artificial neural network that uses an unsupervised training process, which results in finding general patterns of circulation behavior. The SOM is trained with mean sea level pressure (MSLP) anomalies. Widespread extreme events, defined as at least 25 grid points experiencing 99 th percentile precipitation, are examined using SOMs. Widespread extreme days are mapped onto the SOM of MSLP anomalies, indicating circulation patterns. SOMs aids in determining high frequency nodes and hence, circulations conducive to extremes. Multiple circulation patterns are responsible for extreme days, which are differentiated by where extreme events occur in Alaska. Additionally, several meteorological fields are composited for nodes accessed by extreme and non-extreme events to determine specific conditions necessary for a widespread extreme event. Individual and adjacent node composites produce more physically reasonable circulations as opposed to composites of all extremes, which include multiple synoptic regimes. Temporal evolution of extreme events is also traced through SOM space. Thus, this analysis lays the groundwork for diagnosing differences in atmospheric circulations and their associated widespread, extreme precipitation events.

Description: On March 23, 2012, our all-sky imager (ASI) recorded a concentric, ring-like gravity wave pattern. The wave arose within the area covered by images of both OH and O( 1 S ) nightglow emissions taken at the Andes Lidar Observatory (ALO), Chile (30.3°S, 70.7°W). We have estimated the observed and intrinsic parameters of the event and located the wave source within the lower mesosphere altitude range using a reverse ray tracing method. By the analysis of GOES and LIS satellite images, we have not found evidence of neither convective nor lightning activity nearby ALO, indicating that the source of the ring-like wave was not directly in the troposphere. The absence of tropospheric activity and the height of the source of the event suggest that a secondary wave generation mechanism might be the cause of the ring-like wave. The secondary wave mechanism was likely triggered by a breaking, larger scale primary wave excited by deep convection ∼1400 km northeast of ALO over Bolivia, as determined by a forward ray tracing scheme.

Description: This study investigates the kinematic and microphysical control of lightning properties, particularly those that may govern the production of nitrogen oxides (NO X  = NO + NO 2 ) via lightning (LNO X ), such as flash rate, type and extent. The NASA Lightning Nitrogen Oxides Model (LNOM) is applied to lightning observations following multicell thunderstorms through their lifecycle in a Lagrangian sense over Northern Alabama on 21 May 2012 during the Deep Convective Clouds and Chemistry (DC3) experiment. LNOM provides estimates of flash rate, type, channel length distributions, channel segment altitude distributions (SADs) and LNO X production profiles. The LNOM-derived lightning characteristics and LNO X production are compared to the evolution of radar inferred updraft and precipitation properties. Inter-, intra-cloud (IC) flash SAD comprises a significant fraction of the total (IC + cloud-to-ground [CG]) SAD, while increased CG flash SAD at altitudes 〉6 km occurs after the simultaneous peaks in several thunderstorm properties (i.e., total [IC + CG] and IC flash rate, graupel volume/mass, convective updraft volume and maximum updraft speed). At heights 〈6 km, the CG LNO X production dominates the column integrated total LNO X production. Unlike the SAD, total LNO X production consists of a more equal contribution from IC and CG flashes for heights 〉6 km. Graupel volume/mass, updraft volume and maximum updraft speed are all well correlated to the total flash rate (correlation coefficient, ρ ≥0.8) but are less correlated to total flash extent (ρ ≥0.6) and total LNO X production (ρ ≥0.5). Although LNOM transforms lightning observations into LNO X production values, these values are estimates and are subject to further independent validation.

Description: In this study we show that the robust surface ocean currents around Peninsular Florida, namely the Loop and the Florida Currents, affect the terrestrial wet season of Peninsular Florida. We show this through two novel regional coupled ocean–atmosphere models with different bathymetries that dislocate and modulate the strength of these currents and thereby affect the overlying SST and upper ocean heat content. This study show that a weaker current system produces colder coastal SST's along the Atlantic coast of Florida that reduces the length of the wet season and the total seasonal accumulation of precipitation over Peninsular Florida relative to the regional climate model simulation, in which these currents are stronger. The moisture budget reveals that as a result of these forced changes to the temperature of the upper coastal Atlantic Ocean, overlying surface evaporation and atmospheric convection is modulated. This consequently changes the moisture flux convergence leading to the modulation of the terrestrial wet season rainfall over Peninsular Florida that manifests in changes in the length and distribution of daily rain rate of the wet season. The results of this study have implications on interpreting future changes to hydroclimate of Peninsular Florida owing to climate change and low frequency changes to the Atlantic meridional overturning circulation that comprises of the Loop and the Florida Currents as part of its upper branch.

Description: Based on measurements of ultraviolet radiation (UV) for the period 2005-2014 that were obtained from the Chinese Ecosystem Research Network (CERN), we developed an efficient model to estimate UV radiation under various sky conditions. This model can provide an accurate reconstruction of UV radiation data with absolute mean bias error less than 9.65%. We combined this reconstruction model with a hybrid model to obtain the historical dataset of daily UV radiation from 1961 to 2014 at 37 weather stations belonging to the China Meteorological Administration (CMA) over the Tibetan Plateau (TP). Based on the historical dataset, the spatial distribution and temporal variation of UV radiation over the TP region were discussed. The decreasing and increasing periods of ultraviolet radiation over the TP were significantly different from those over the entire China. There was an increasing trend in UV radiation over the TP from 1961 to 1983, followed by a decreasing one until 2014; while UV radiation decreased from 1961 to 1989 and then increased slightly after 1989 for the entire China. The average UV radiation values in the increasing and decreasing periods over the TP were 0.598 MJ · m -2  · d -1 and 0.594 MJ · m -2  · d -1 , respectively. In addition, aerosol optical depth, column ozone and cloud prevent approximately 7.13%, 1.31%, and 15.05% of UV radiation reaching the Earth's surface respectively.

Description: To assess marine boundary layer (MBL) cloud simulations in three versions of the Community Atmosphere Model (CAM), three sets of short-term global hindcasts are performed and compared to Atmospheric Radiation Measurement (ARM) program observations on Graciosa Island in the Azores from June 2009 to December 2010. The three versions consist of CAM5.3 with default schemes (CAM5.3), CAM5.3 with Cloud Layers Unified By Binormals (CLUBB-MG1), and CAM5.3 with CLUBB and updated microphysics scheme (CLUBB-MG2). Our results show that relative to CAM5.3 default schemes, simulations with CLUBB better represent MBL cloud-base height, the height of the major cloud layer, and the daily cloud cover variability. CLUBB also better simulates the relationship of cloud fraction to cloud liquid water path (LWP) most likely due to CLUBB's consistent treatment of these variables through a probability distribution function (PDF) approach. Sub-cloud evaporation of precipitation is substantially enhanced in simulations with CLUBB-MG2 and is more realistic based on the limited observational estimate. Despite these improvements, all model versions underestimate MBL cloud cover. CLUBB-MG2 reduces biases in in-cloud LWP (clouds are not too bright) but there are still too few of MBL clouds due to an underestimate in the frequency of overcast scenes. Thus combining CLUBB with MG2 scheme better simulates MBL cloud processes, but because biases remain in MBL cloud cover CLUBB-MG2 does not improve the simulation of the surface shortwave cloud radiative effect ( CRE SW ).

Description: Four regional climate model runs centered on the Southeast United States (SEUS) assuming a crop growing season of May through October are irrigated at 25% (IRR25), 50% (IRR50), 75% (IRR75) and 100% (IRR100) of the root zone porosity to assess the sensitivity of the SEUS climate to irrigation. A fifth run, assuming no irrigation (CTL), is used as the basis for comparison. Across all IRR runs, it is found that there is a general reduction in seasonal mean precipitation over the irrigated cells relative to CTL. This manifests as an increase in dry (0-1 mm/day) days and reduction in 〉 1 mm/day rainfall events. A comparative moisture budget reveals that area-averaged precipitation over the irrigated cells displays a reduction in precipitation and runoff in IRR100 with a weaker reduction in IRR25. This is despite an increase in vertically integrated moisture convergence and local evaporation. We find that irrigation increases the lower atmospheric stability, which in turn reduces the convective rainfall over the irrigated areas. Seasonally averaged temperatures reduce over irrigated areas, with the intensity of the reduction increasing with irrigation vigor. This is largely attributed to a repartitioning of sensible heat flux into latent heat flux. There is also however a small increase of heat flow to deeper soil layers. Precipitation ahead of transient cold fronts is also reduced by irrigation as they pass over irrigated cells, owing to the increased stability in the lower troposphere. The intensity of this precipitation reduction becomes more intense as irrigation vigor increases. Lastly, heat waves in the SEUS are reduced in intensity over irrigated cells.

Description: Precipitation totals in the greater Caribbean are known to be affected by interannual variability. In particular, dry conditions in the spring-summer have been physically linked to the positive phase of North Atlantic Oscillation (NAO) in the literature. In this study, it was found through regression analysis that an active Madden-Julian Oscillation (MJO) in winter geographically focused over the Maritime Continent contributes to a positive NAO in March via the generation of Rossby waves in the Northern Hemisphere. Specifically, a negative Pacific North American pattern develops in the winter and transitions to an Atlantic pattern in spring. The positive NAO is a transient feature of this evolving wavetrain, but a center of significant positive 200 hPa geopotential heights is entrenched over the Southeast U.S. throughout the February to May time period and is manifested as high pressure at the surface. The southern flank of this system increases the speeds of the tradewinds and leads to a cooling of the Caribbean SSTs and thus convection suppression and reduced precipitation. Thus, this study advances our understanding of the climate of the greater Caribbean by using climate teleconnections to relate the MJO to rainfall in the region.

Description: Uncertainties in projecting the changes in hydroclimatic variables (i.e., temperature, precipitation) under climate change partly arises from the inability of Global Circulation Models (GCMs) in explaining the observed changes in hydrologic variables. Apart from the unexplained changes by GCMs, the process of customizing GCM projections to watershed scale through a model chain – spatial downscaling, temporal disaggregation and hydrologic model – also introduces errors, thereby limiting the ability to explain the observed changes in hydrologic variability. Towards this, we first propose metrics for quantifying the errors arising from different steps in the model chain in explaining the observed changes in hydrologic variables (streamflow, groundwater). The proposed metrics are then evaluated using a detailed retrospective analyses in projecting the changes in streamflow and groundwater attributes in four target basins that span across a diverse hydroclimatic regimes over the US Sunbelt. Our analyses focused on quantifying the dominant sources of errors in projecting the changes in eight hydrologic variables – mean and variability of seasonal streamflow, mean and variability of 3-day peak seasonal streamflow, mean and variability of 7-day low seasonal streamflow and mean and standard deviation of groundwater depth – over four target basins using an Penn state Integrated Hydrologic Model (PIHM) between the period 1956-1980 and 1981-2005. Retrospective analyses show that small/humid (large/arid) basins show increased (reduced) uncertainty in projecting the changes in hydrologic attributes. Further, changes in error due to GCMs primarily account for the unexplained changes in mean and variability of seasonal streamflow. On the other hand, the changes in error due to temporal disaggregation and hydrologic model account for the inability to explain the observed changes in mean and variability of seasonal extremes. Thus, the proposed metrics provide insights on how the error in explaining the observed changes being propagated through the model under different hydroclimatic regimes.

Description: Simulations from 13 highly resolved regional climate models (RCM) run within the CORDEX initiative at 0.11°resolution with boundary forcings from five different CMIP5 global models are employed to derive future climate change signal for the Greater Alpine Region (GAR) and four smaller investigation areas. Evaluation statistics include mean temperature and precipitation, frequency of days with precipitation over 1 mm and over 15 mm, 90% quantile of the frequency distribution, and maximum number of consecutive dry days. The evaluation for the period from 1971 to 2000 indicates that the models reproduce spatial seasonal precipitation patterns. In general, the simulations underestimate the seasonal mean temperature and overestimate the mean precipitation values. In GAR the ensemble seasonal mean temperature bias ranges from -0.8 to -1.9 °C. The bias in precipitation varies between +14.8% in summer and +41.6% in the winter season. Larger errors are found for other statistics and in the investigated regions. In general, no significant gains in the quality of reproduction of the observed precipitation and temperature statistics compared to previous experiments can be identified. The temperature calculations for 2071–2100 related to the period from 1971 to 2000 in the GAR area show ensemble mean increases in the seasonal mean 2 m temperature of 2.5 °C in fall and winter, 2.4 °C in summer and 1.9 °C in spring. In the same area, precipitation is simulated to increase up to 12.3% in winter and 5.7% in spring. Only minor changes of the ensemble mean are predicted with +2.3% in fall and -1.7% in summer.

Description: We present the first simultaneous and common-volume observations of mesospheric K and Na densities and temperature conducted by a K Doppler lidar and a Na lidar at the Arecibo Observatory (18.35°N, 66.75°W), Puerto Rico. Measurements reported here were conducted on three nights with 9, 6 and 7 hours of observations in December 2003 and January 2004. The behaviors of the Na and K layer and the temperature variations showed that the bottom edges of the Na and K layers matched one another almost exactly. Layer peak and column densities increased/decreased together with temperature for the Na layer, but not for the K layer. The correlation between temperature and density fluctuations was strongly positive at and just below the peak altitude of the nightly mean density profile but transitioned to negative several kilometers above the respective peak of either Na or K. The peak densities of the sporadic Na and K layers occurring at low altitudes did not behave in the same manner especially when the background temperature decreased. We discuss, qualitatively, the impact of dynamical and chemical effects on the behaviors of the Na and K layers. Our analysis suggests that wave-induced dynamical transport can account for the observed correlations between temperature, Na density and K density fluctuations. Dynamical transport and wave-induced chemical transport have similar effects on the behaviors of the Na and K layers. The resulting differences in Na and K layers are qualitatively consistent with different dependences on temperature of the Na and K chemistries.

Description: The changes of atmospheric flow patterns related to Arctic Amplification have impacts well beyond the Arctic regional weather and climate system. Here we examine modulations of vertically propagating planetary waves, a major feature of the climate response to Arctic sea ice reduction by comparing the corresponding results of an atmospheric general circulation model with reanalysis data for periods of high and low sea ice conditions. Under low sea ice condition we find enhanced coupling between troposphere and stratosphere starting in November with preferred polar stratospheric vortex breakdowns in February, which then feeds back to the troposphere. The model experiment and ERA-Interim reanalysis data agree well with respect to temporal and spatial characteristics associated with vertical planetary wave propagation including its precursors. The upward propagating planetary wave anomalies resemble a wave number 1 and 2 pattern depending on region and timing. Since our experimental design only allows influences from sea ice changes and there is a high degree of resemblance between model results and observations, we conclude that sea ice is a main driver of observed winter circulation changes.

Description: This study presents aircraft spiral ascent and descent observations intercepting a transition to riming processes during widespread stratiform precipitation. The sequence is documented using collocated scanning and profiling radar, including longer-wavelength dual-polarization measurements and shorter-wavelength Doppler spectra. Riming regions are supported using aircraft measurements recording elevated liquid water concentrations, spherical particle shapes, and saturation with respect to water. Profiling cloud radar observations indicate riming regions during the event as having increasing particle fall speeds, rapid time-height changes, and bimodalities in Doppler spectra. These particular riming signatures are coupled to scanning dual-polarization radar observations of higher differential reflectivity (Z DR ) aloft. Reduced melting layer enhancements and delayed radar bright-band signatures in the column are also observed during riming periods, most notably with the profiling radar observations. The bimodal cloud radar Doppler spectra captured near riming zones indicate two time-height spectral ice peaks; one rimed particle peak and one peak associated with pristine ice needle generation and/or growth between -4 °C and -7 °C also sampled by aircraft probes. This pristine needle population gives a partial explanation for the enhanced Z DR we observe near this rimed particle region. The riming signatures aloft and radar measurements within the melting level are weakly lag correlated (r ~ 0.6) with smaller median drop sizes at the surface, as compared with later times when aggregation of larger particle sizes was believed dominant.

Description: We study the evolution of warm convective cloud fields using large eddy simulations of continental and trade cumulus. Individual clouds are tracked a posteriori from formation to dissipation using a 3D cloud tracking algorithm and results are presented in the phase-space of center of gravity altitude versus cloud liquid water mass (CvM space). The CvM space is shown to contain rich information on cloud field characteristics, cloud morphology, and common cloud development pathways, together facilitating a comprehensive understanding of the cloud field. In this part we show how the meteorological (thermodynamic) conditions that determine the cloud properties are projected on the CvM phase space and how changes in the initial conditions affect the clouds' trajectories in this space. This part sets the stage for a detailed microphysical analysis that will be shown in part II.

Description: We use a modified version of the tropical leaky pipe (TLP) model of the stratosphere to explore how well an idealized model can (1) reproduce global chemistry-climate model (CCM) output and (2) constrain transport characteristics necessary to replicate measurements of long-lived trace gases. The version of the TLP model we use includes the simulation of long-lived trace gases, such as SF 6 and CO 2 , as well as photochemically active trace gases such as CFC-11, CFC-12 and N 2 O. The TLP model was found to accurately replicate trace gas output from the Canadian Middle Atmosphere Model (CMAM) for time-averaged profiles in the tropics and each extratropical region. Given confidence that the TLP model represents the basic transport features in CMAM we then used the TLP model to interpret differences between CMAM output and measurements from the Atmospheric Chemistry Experiment (ACE) and balloons. The TLP model is shown to uniquely determine residual mean circulation and recirculation (mixing between the extratropics and tropics) changes necessary for CMAM to more accurately simulate the measurements. Such guidance on these transport parameters is novel due to the relatively high precision and the simultaneous derivation of important parameters, as compared to previous studies. The TLP model can ideally be used as a bridge between measurements and CCMs to potentially allow more targeted modification of the CCMs than would otherwise be possible.

Description: Large-scale modeling of glacier mass balance relies often on the output from regional climate models (RCMs). However, the limited accuracy and spatial resolution of RCM output poses limitations on mass balance simulations at sub-regional or local scales. Moreover, RCM output is still rarely available over larger regions or for longer time periods. This study evaluates the extent to which it is possible to derive reliable region-wide glacier mass balance estimates, using coarse-resolution (10 km) RCM output for model forcing. Our data cover the entire Svalbard archipelago over one decade. To calculate mass balance we use an index-based model. Model parameters are not calibrated, but the RCM air temperature and precipitation fields are adjusted using in situ mass balance measurements as reference. We compare two different calibration methods: root mean square error minimization and regression optimization. The obtained air temperature shifts (+1.43 °C vs. +2.22 °C) and precipitation scaling factors (1.23 vs. 1.86) differ considerably between the two methods, which we attribute to inhomogeneities in the spatiotemporal distribution of the reference data. Our modeling suggests a mean annual climatic mass balance of -0.05 ± 0.40 m w.e. a -1 for Svalbard over 2000-2011, and a mean equilibrium line altitude of 452 ± 200 m a.s.l. We find that the limited spatial resolution of the RCM forcing with respect to real surface topography and the usage of spatially homogeneous RCM-output adjustments and mass balance-model parameters are responsible for much of the modeling uncertainty. Sensitivity of the results to model-parameter uncertainty is comparably small and of minor importance.

Description: Land surface models (LSMs) are a key tool to enhance process understanding and to provide predictions of the terrestrial hydrosphere and its atmospheric coupling. Distributed LSMs predict hydrological states and fluxes, such as land surface temperature (LST) or actual evapotranspiration (aET), at each grid cell. LST observations are widely available through satellite remote sensing platforms that enable comprehensive spatial validations of LSMs. In spite of the great availability of LST data, most validation studies rely on simple cell to cell comparisons and thus do not regard true spatial pattern information. The core novelty of this study is the development and application of two innovative spatial performance metrics, namely EOF- and connectivity-analysis, to validate predicted LST patterns by three LSMs (Mosaic, Noah, VIC) over the contiguous USA. The LST validation dataset is derived from global High-Resolution-Infrared-Radiometric-Sounder (HIRS) retrievals for a 30 year period. The metrics are bias insensitive, which is an important feature in order to truly validate spatial patterns. The EOF analysis evaluates the spatial variability and pattern seasonality, and attests better performance to VIC in the warm months and to Mosaic and Noah in the cold months. Further, more than 75% of the LST variability can be captured by a single pattern that is strongly correlated to air temperature. The connectivity analysis assesses the homogeneity and smoothness of patterns. The LSMs are most reliable at predicting cold LST patterns in the warm months and vice versa. Lastly, the coupling between aET and LST is investigated at flux tower sites and compared against LSMs to explain the identified LST shortcomings.

Description: Ice nucleating particles (INPs) are required for initial ice crystal formation in clouds at temperatures warmer than about -36 °C and thus play a crucial role in cloud and precipitation formation. Biomass burning has been found to be a source of INPs in previous studies, and is also a major contributor to atmospheric black carbon (BC) concentrations. This study focuses on isolating the BC contribution to the INP population associated with biomass combustion. Emissions of condensation mode INPs from a number of globally relevant biomass fuels were measured at -30 °C and above water saturation as fires progressed from ignition to extinguishment in a laboratory setting. Number emissions of INPs were found to be highest during intense flaming combustion (modified combustion efficiency 〉 0.95). Overall, combustion emissions from 13 of 22 different biomass fuel types produced measurable INP concentrations for at least one replicate experiment. On average, all burns that produced measureable INPs had higher combustion efficiency, which is associated with higher BC emissions, than those that did not produce measureable INPs. Across all burns that produced measureable INPs, concentrations ranged from 0.1 – 10 cm -3 and the median emission factor was about 2 × 10 7 INPs per kilogram of fuel burned. For a subset of the burns, the contribution of refractory black carbon (rBC) to INP concentrations was determined by removing rBC via laser induced incandescence (LII). Reductions in INPs of 0 – 70% were observed, indicating an important contribution of rBC particles to INP concentrations for some burns, especially marsh grasses.

Description: Q-bursts are globally detectable extremely low frequency (ELF, 3-3000 Hz) band wave packets produced by intense lightning discharges. Q-bursts recorded in the Széchenyi István Geophysical Observatory (NCK, 16.7 E, 47.6 N), Hungary on 1 and 2 August, 2012 have been analyzed to find azimuths of their sources. The location of parent lightning strokes of 320 and 205 Q-bursts on the two days, respectively, have been identified in the records of the World Wide Lightning Location Network (WWLLN) using the detection times at NCK. ELF data-based source azimuths were found to differ systematically from source azimuths obtained from WWLLN lightning locations. The difference between the corresponding azimuth values depends on the azimuth of the source. This variation of the source azimuth error mirrors the symmetry of the conductance of the Earth's crust inferred from magnetotelluric measurements around NCK. After correction for the azimuthal dependence, the variation of the residual error shows a diurnal pattern with positive azimuth deviations occurring near midnight, local time. Füllekrug and Sukhorukov (1999) suggested that the anisotropic conductivity in the Earth's crust below the observatory and the different daytime and nighttime conductivities in the lower ionosphere, respectively, may cause the identified error terms. Our results emphasize the substantial effect of anisotropic conductivity in the Earth's crust around the recording station on the accuracy of ELF direction finding. The need for theoretical approach and more measurements is pointed in understanding the underlying mechanisms quantitatively and in investigating whether ELF observations can be used in geophysical prospecting.

Description: Aromatic hydrocarbons are important anthropogenic precursors of tropospheric ozone and secondary organic aerosols. Here, we measured ambient aromatic hydrocarbons from March 2012 to February 2014 at six rural sites in China's developed coastal regions. On average, benzene (B) comprised 〉 50% of total benzene (B), toluene (T), ethylbenzene (E), and xylenes (X) (BTEX) at sites in the Northeast China Plain (NECP) or in the North China Plain (NCP), whereas T, E, and X accounted for 〉 77% of total BTEX at sites in the Yangtze River Delta (YRD) and the Pearl River Delta (PRD) in the south. BTEX at the northern sites was significantly correlated ( p  〈 0.01) with combustion tracer-carbon monoxide (CO) but weakly correlated with traffic marker-methyl tert-butyl ether (MTBE), suggesting that their main sources were coal and biofuel/biomass burning with substantially elevated B levels during the winter heating period. In contrast, BTEX at the southern sites originated mainly from traffic-related and/or industrial emission sources, as indicated by the poor correlations with CO but highly significant ( p  〈 0.01) correlations with MTBE and tetrachloroethylene, an industrial emission tracer. The B/CO emission ratios from measurement agreed within a factor of two with that of a previous widely used emission inventory of China, but the T/CO ratio at the NECP site and the o-X/CO ratio at the NCP site were 29% and 38% of that in the inventory, respectively; the E/CO and X/CO ratios at the YRD site were 3.2-3.5 fold that in the emission inventory.

Description: The bi-spectral method retrieves cloud optical thickness ( τ ) and cloud droplet effective radius ( r e ) simultaneously from a pair of cloud reflectance observations, one in a visible or near infrared (VIS/NIR) band and the other in a shortwave-infrared (SWIR) band. A cloudy pixel is usually assumed to be horizontally homogeneous in the retrieval. Ignoring sub-pixel variations of cloud reflectances can lead to a significant bias in the retrieved τ and r e . In the literature, the retrievals of τ and r e are often assumed to be independent and considered separately when investigating the impact of sub-pixel cloud reflectance variations on the bi-spectral method. As a result, the impact on τ is contributed only by the sub-pixel variation of VIS/NIR band reflectance and the impact on r e only by the sub-pixel variation of SWIR band reflectance. In our new framework, we use the Taylor expansion of a two-variable function to understand and quantify the impacts of sub-pixel variances of VIS/NIR and SWIR cloud reflectances and their covariance on the τ and r e retrievals. This framework takes into account the fact that the retrievals are determined by both VIS/NIR and SWIR band observations in a mutually dependent way. In comparison with previous studies, it provides a more comprehensive understanding of how sub-pixel cloud reflectance variations impact the τ and r e retrievals based on the bi-spectral method. In particular, our framework provides a mathematical explanation of how the sub-pixel variation in VIS/NIR band influences the r e retrieval and why it can sometimes outweigh the influence of variations in the SWIR band and dominate the error in r e retrievals, leading to a potential contribution of positive bias to the r e retrieval. We test our framework using synthetic cloud fields from a large-eddy simulation and real observations from MODIS. The predicted results based on our framework agree very well with the numerical simulations. Our framework can be used to estimate the retrieval uncertainty from sub-pixel reflectance variations in operational satellite cloud products and to help understand the differences in τ and r e retrievals between two instruments.

Description: Observations of surface direct solar radiation (DSR) and visibility, particulate matter with aerodynamic diameters less than 2.5 µm (PM 2.5 ), together with the Aerosol Optical Thickness (AOT) taken from Moderate-resolution Imaging Spectroradiometer (MODIS) and Multiangle Imaging SpectroRadiometer (MISR), were investigated to gain insight into the impact of aerosol pollution on surface solar radiation in China. The surface DSR decreased during 2004-2014 compared with 1993 ~ 2003 over eastern China, but no clear reduction was observed in remote regions with cleaner air. Significant correlations of visibility, PM 2.5 and regionally averaged AOT with the surface DSR over eastern China indicate that aerosol pollution greatly affects the energy available at the surface. The net loss of surface solar radiation also reduces the surface ground temperature (SGT) over eastern China. However, the slope of the linear variation of the radiation with respect to atmospheric visibility is distinctly different at different stations, implying that the main aerosol type varies regionally. The largest slope value occurs at Zhengzhou and indicates that the aerosol absorption in central China is the highest, and lower slope values suggest relatively weakly-absorbing types of aerosols at other locations. The spatial distribution of the linear slopes agrees well with the geographical distribution of the absorbing aerosols derived from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations and Ozone Monitoring Instrument over China. The regional correlation between a larger slope value and higher absorbance properties of aerosols indicates that the net effects of aerosols on the surface solar energy and corresponding climatic effects are dependent on both aerosol amount and optical properties.

Description: To optimize the description of land surface processes and improve climate simulations over the Tibetan Plateau (TP), a modified soil water–heat parameterization scheme (SWHPS) is implemented into the Community Land Model 3.5 (CLM3.5), which is coupled to the Regional Climate Model 4 (RegCM4). This scheme includes Johansen's soil thermal conductivity scheme together with Niu's groundwater module. Two groups of climate simulations are then performed using the original RegCM4 and revised RegCM4 to analyze the effects of the revised SWHPS on regional climate simulations. The effect of the revised RegCM4 on simulated air temperature is relatively small (with mean biases changing by less than 0.1 °C over the TP). There are overall improvements in the simulation of winter and summer air temperature, but increased errors in the eastern TP. It has a significant effect on simulated precipitation. There is also a clear improvement in simulated annual and winter precipitation, particularly over the northern TP, including the Qilian Mountains and the source region of the Yellow River. There are, however, increased errors in precipitation simulation in parts of the southern TP. The precipitation difference between the two models is caused mainly by their convective precipitation difference, particularly in summer. Overall, the implementation of the new SWHPS into the RegCM4 has a significant effect not only on land surface variables, but also on the overlying atmosphere through various physical interactions.

Description: To detect the frequency and intensity of precipitation extremes in China for the middle 21 st century, simulations were conducted with the regional climate model RegCM4 forced by the global climate model GFDL_ESM2M under the middle emission scenario (RCP4.5). Compared with observed precipitation extremes for the reference period from 1982 to 2001, RegCM4 generally performed better in most river basins of China relative to GFDL. In the future period 2032–2051, more wet extremes will occur relative to the present period in most study areas, especially in southeast China while significantly less dry extremes will occur in arid and semi-arid areas in northwest China. In contrast, areas in northwest China showed an increase in the trend of dry extremes (CDD) and a decrease in the trend of wet extremes (R95p and Rx5day), which might result in more drought in the future. Finally, we discuss in detail the possible reason of these processes, such as zonal wind, vertical wind, water vapor, etc. In the Huaihe river basin (HU), reduced south winds in summer (JJA) and a decrease of the upward vertical p-velocity cause less future precipitation and might lead to changes of extreme events. We also completed correlation analysis between the precipitation extreme indices and the climate factors and found that the precipitation extremes were more sensitive to the annual and seasonal mean precipitation, total water vapor, and upward vertical wind relative to the geopotential height (GPH) and 2 m temperature over most river basins in China. Perhaps the changes of some wet extremes could be verified partly through changes of annual precipitation due to their high consistence.

Description: Black carbon (BC) plays an important role on the global and regional climate, whereas there are significant uncertainties on its optical properties. Among various optical properties, the Ångström exponent ( AE ) indicates the spectral variation of the particle-optic interaction, and is widely used to understand the aerosol properties. We consider the influence of BC geometry on its optical properties, and assess the sensitivity of the AE to particle geometry and size distribution. The fractal aggregates with different fractal dimensions are used to represent realistic BC particles, and popular equivalent volume spherical and spheroidal models are also considered for comparison. Even if the fractal aggregates become highly compact and spherical, their optical properties are still significantly different from those of equivalent volume spheres or spheroids. Meanwhile, the Rayleigh-Debye-Gans approximation can hardly provide accurate results for all optical quantities of aggregates with different dimensions. The extinction Ångström exponent ( EAE ) and absorption Ångström exponent ( AAE ) are sensitive to both particle geometry and size distribution. With BC becoming more compact (from fractal aggregate to spheroid, and to sphere), the AE becomes more sensitive to particle size distribution. The EAE and AAE of aggregates with different size distributions varies between 1.10-1.63 and 0.87-1.50, respectively, whereas those of the spheres or spheroids have wider ranges. Furthermore, the AE at smaller wavelengths (between 0.35 µm and 0.55 µm) is more sensitive to geometry and size distribution than that given by optical properties at larger wavelengths (between 0.55 µm and 0.88 µm).

Description: The land surface temperature can be estimated from satellite passive microwave observations, with limited contamination from the clouds as compared to the infrared satellite retrievals. With ∼60 % cloud cover in average over the globe, there is a need for “all weather”, long record, and real-time estimates of land Surface Temperature (Ts) from microwaves. A simple yet accurate methodology is developed to derive the land surface temperature from microwave conical scanner observations, with the help of pre-calculated land surface microwave emissivities. Different tests are conducted to optimize the algorithms. The method is applied to the SSM/I observations over two years, regardless of the cloud cover. The results are compared to infrared estimates from ISCCP and from AATSR, under clear sky conditions. Limited biases are observed (∼0.5 K for both comparisons) with a root mean square error (rmse) of ∼5 K, to be compared to the rmse of ∼3.5 K between ISCCP et AATSR. Cloud contamination in the AATSR estimates have been evidenced and a simple filtering has been proposed. The microwave surface temperatures have also been carefully compared to in situ Ts time series from a collection of more than 20 stations over a large range of environments. Very good agreement is obtained for well-controlled stations in vegetated environments (down to rmse of ∼2.5 K for several stations), but the methodology encounter difficulties under cold conditions due to the large variability of snow and ice surface emissivities.

Description: Sub-grid information from land models has the potential to be a powerful tool for investigating land-atmosphere interactions, but relatively few studies have attempted to exploit sub-grid output. In this study, we modify the configuration of the Community Land Model version CLM4.5 so that each plant functional type (PFT) is assigned its own soil column. We compare sub-grid and grid cell-averaged air temperature and surface energy fluxes from this modified case (PFTCOL) to a case with the default configuration—a shared soil column for all PFTs (CTRL), and examine the difference in simulated surface air temperature between grass and tree PFTs within the same grid cells (ΔT GT ). The magnitude and spatial patterns of ΔT GT from PFTCOL agree more closely with observations, ranging from -1.5 K in boreal regions to +0.6 K in the tropics. We find that the column configuration has a large effect on PFT-level energy fluxes. In the CTRL configuration, the PFT-level annual mean ground heat flux (G) differs substantially from zero. For example, at a typical tropical grid cell, the annual G is 31.8 Wm -2 for the tree PFTs and -14.7 Wm -2 for grass PFTs. In PFTCOL, G is always close to zero. These results suggest that care must be taken when assessing local land cover change impacts with sub-grid information. For models with PFTs on separate columns, it may be possible to isolate the differences in land surface fluxes between vegetation types that would be associated with land cover change from other climate forcings and feedbacks in climate model simulations.

Description: Infrasonic waves propagate at long ranges through atmospheric ducts resulting from the stratification of atmospheric properties. In order to study the infrasonic wave propagation, we resort to atmospheric specification combining Numerical Weather Prediction and climatological models. However, these models do not describe small scale variability such as perturbations associated to the presence of internal gravity waves. These waves play an important role in the atmospheric dynamic by transferring momentum to the mean flow at critical levels and at wave-breaking altitudes. In this study we intend to describe the interaction of infrasonic waves with internal gravity waves in order to understand the extended wavetrains observed in broadband infrasound signals. We use a numerical model for the propagation of internal waves to generate realistic perturbations of the background atmospheric states. By using a linear full-wave model of infrasound propagation, our goal is to ultimately relate infrasound characteristics to internal waves properties. We apply those numerical models to different atmospheric mean states including gravity wave perturbations and compare the simulations to infrasound signals recorded from rocket motor fuel elimination events at the Utah Test and Training Range (UTTR). Our results, based on an intensive simulation of infrasound waveforms, show that combining atmospheric background with gravity wave propagation model is relevant to explain, to first-order, the behavior of the infrasound field at the distance of the first stratospheric arc. In particular we obtain a better match between pulse duration and peak-to-peak amplitude along the stratospheric arc. Such study support the use of gravity wave simulation in conjunction with infrasound modeling in order to improve gravity wave parameterization in Numerical Weather Forecasting.

Description: Black carbon (BC) is usually mixed with other aerosol species within individual aerosol particles. This mixture, along with the particles' size and morphology, determines the particles' optical and cloud condensation nuclei properties, and hence black carbon's climate impacts. In this study, the particle-resolved aerosol model PartMC-MOSAIC was used to quantify the importance of black carbon mixing state for predicting cloud microphysical quantities. Based on a set of about 100 cloud parcel simulations a process-level analysis framework was developed to attribute the response in cloud microphysical properties to changes in the underlying aerosol population (“plume effect”) and the cloud parcel cooling rate (“parcel effect”). In most of the simulations the plume and parcel effects had opposite signs, with the plume effect dominating. The response of cloud droplet number concentration to changes in BC emissions depended on the BC mixing state. When the aerosol population contained mainly aged BC, an increase in BC emission increased cloud droplet number concentrations (“additive effect”). In contrast, when the aerosol population contained mainly fresh BC particles, they act as sinks for condensable gaseous species, resulting in decreasing cloud droplet number concentration as BC emissions were increased (“competition effect”). Additionally, we quantified the error in cloud microphysical quantities when neglecting the information on BC mixing state. The errors ranged from −12% to +45% for the cloud droplet number fraction, from 0% to +1022% for the nucleation-scavenged BC mass fraction, from −12% to +4% for the effective radius, and from −30% to +60% for the relative dispersion.

Description: We present in situ airborne measurements of methane (CH 4 ) and ethane (C 2 H 6 ) taken aboard a NOAA DHC-6 Twin Otter research aircraft in May 2014 over the Williston Basin in northwestern North Dakota, a region of rapidly growing oil and natural gas production. The Williston Basin is best known for the Bakken shale formation, from which a significant increase in oil and gas extraction has occurred since 2009. We derive a CH 4 emission rate from this region using airborne data by calculating the CH 4 enhancement flux through the planetary boundary layer downwind of the region. We calculate CH 4 emissions of (36 ± 13), (27 ± 13), (27 ± 12), (27 ± 12), and (25 ± 10) × 10 3  kg/hr from five transects on three days in May 2014 downwind of the Bakken shale region of North Dakota. The average emission, (28 ± 5) × 10 3  kg/hr, extrapolates to 0.25 ± 0.05 Tg/yr, which is significantly lower than a previous estimate of CH 4 emissions from northwestern North Dakota and southeastern Saskatchewan using satellite remote sensing data. We attribute the majority of CH 4 emissions in the region to oil and gas operations in the Bakken based on the similarity between atmospheric C 2 H 6 to CH 4 enhancement ratios and the composition of raw natural gas withdrawn from the region.

Description: Coincident profiling observations from Doppler lidars and radars are used to estimate the turbulence energy dissipation rate (ε) using three different data sources: i) Doppler radar velocity (DRV), ii) Doppler lidar velocity (DLV), and iii) Doppler radar spectrum width (DRW) measurements. The agreement between the derived ε estimates is examined at the cloud base height of stratiform warm clouds. Collocated ε estimates based on power spectra analysis of DRV and DLV measurements show good agreement (correlation coefficient of 0.86 and 0.78 for both cases analyzed here) during both drizzling and non-drizzling conditions. This suggests that unified (below and above cloud base) time-height estimates of ε in cloud-topped boundary layer conditions can be produced. This also suggests that eddy dissipation rate can be estimated throughout the cloud layer without the constraint that clouds need to be non-precipitating. Eddy dissipation rate estimates based on DRW measurements compare well with the estimates based on Doppler velocity but their performance deteriorates as precipitation size particles are introduced in the radar volume and broaden the DRW values. Based on this finding, a methodology to estimate the Doppler spectra broadening due to the spread of the drop size distribution is presented. The uncertainties in ε introduced by signal-to-noise conditions, the estimation of the horizontal wind, the selection of the averaging time window and the presence of precipitation are discussed in detail.

Description: A self–consistent hydrodynamic model for the solar heating driven onset of a dust devil vortex is derived and analyzed. The toroidal flows and vertical velocity fields are driven by an instability that arises from the inversion of the mass density stratification produced by solar heating of the sandy surface soil. The nonlinear dynamics in the primary temperature gradient driven vertical air flows drives a secondary toroidal vortex flow through a parametric interaction in the nonlinear structures. While an external tangential shear flow may initiate energy transfer to the toroidal vortex flow, the nonlinear interactions dominate the transfer of vertical–radial flows into a fast toroidal flow. This secondary flow has a vertical vorticity while the primary thermal gradient driven–flow produces the toroidal vorticity. Simulations for the complex nonlinear structure are carried out with the passive convection of sand as test particles. Triboelectric charging modeling of the dust is used to estimate the charging of the sand particles. Parameters for a Dust Devil laboratory experiment are proposed considering various working gases and dust particle parameters. The nonlinear dynamics of the toroidal flow driven by the temperature gradient is of generic interest for both neutral gases and plasmas.

Description: The crosstalk phenomena in Terra MODIS Mid-to-Long Wave Infrared (LWIR) Photovoltaic (PV) bands (bands 27-30) have recently been individually studied and characterized, and a correction algorithm has been developed.. The routine calibration of the four LWIR PV bands uses an on-board Black Body (BB) based on a quadratic model for the relationship between the at-aperture radiance and the background subtracted instrument response. While the crosstalk correction has been successfully applied in both the routine BB calibration (scan basis) to correct the crosstalk effect in the linear term and the Earth View (EV) radiance in our previous investigations on the bands 27-29, the most recent work on band 30 demonstrated a newfound necessity to include the impact of the crosstalk effect on the non-linear term as well as the offset. In this paper, we analyze the calibration calculation under a variety of conditions consistent with the MODIS Collection 6 settings to examine the impact of the crosstalk effect in the two terms derived from the BB Warm-Up-Cold-Down (WUCD) calibration. We show that with correct account of the crosstalk effect in the WUCD calibration, the sudden changes and other abnormal features that have been observed in the two terms for many years are effectively and remarkably removed. In addition, imagery for bands 27-29 using the calibration result fully corrected for the electronic crosstalk effect shows further improvement over previous results that account for only the corrected linear term, whereas for the band 30 different testing scenes validate the previous fully corrected findings.

Description: Atmospheric transport of mid-latitude pollutant emissions to the Arctic can result in disproportionate impacts on the receptor region. We use carbon monoxide (CO), a tracer of incomplete combustion, to study changes in pollutant transport to the Arctic. Using a wavelet transform we spectrally decompose CO mole fraction measurements from three Arctic sites (Alert, Barrow and Zeppelin) collected by NOAA over the past 20–25 years. We show that CO concentrations have decreased by -1.0 to -1.2 ppb/yr. We find that the dampened seasonal cycle (-1.2 – -2.3 ppb/yr) is mostly due to a reduction in peak concentrations (-1.5 – -2.4 ppb/yr), which we attribute to reduced source emissions. We find no evidence to support a persistent increase in hydroxyl radical concentration. Using the GEOS-Chem global 3-D chemistry transport model we show that observed decreases are consistent with reductions in fossil fuel usage from Europe and North America.

Description: This study characterizes Lightning Mapping Array performance for networks that participated in the Deep Convective Clouds and Chemistry (DC3) field program using new Monte Carlo and curvature matrix model simulations. These open-source simulation tools are readily adapted to real-time operations or detailed studies of performance. Each simulation accounted for receiver threshold and location, as well as a reference distribution of source powers and flash sizes based on thunderstorm observations and the mechanics of station triggering. Source and flash detection efficiency were combined with solution bias and variability to predict flash area distortion at long ranges. Location errors and detection efficiency were highly dependent on the station configuration and thresholds, especially at longer ranges, such that performance varied more than expected across different networks and with azimuth within networks. Error characteristics matched prior studies, which led to an increase in flash distortion with range. Predicted flash detection efficiency exceeded 95% within 100 km of all networks.

Description: Whereas changes in magnitude of geophysical extremes under climate change have received significant attention, potential concomitant changes in spatial dependence structures have remained unexplored so far. Here, we provide first evidence of such an effect, highlighting a significant trend in the spatial dependence structure of snowfall extremes in the French Alps at decadal time scale. Specifically, we process a comprehensive dataset of winter maximum snowfall from all over the French Alps collected in 90 stations from 1958 to 2012. We estimate extremal dependence over 20-year moving estimation windows taking into account possible anisotropy potentially related to orographic effects and/or patterns in atmospheric flows. For each window, we derive a range representing the distance above which extremes are almost independent. We show that snowfall extremes tended to become less spatially dependent over time, with the dependence range reduced roughly by half during the study period. We demonstrate the connection between this trend and local and synoptic climatic variables associated with the current climate change context. In details, the decreasing pattern in extremal dependence is concomitant with a trend towards less harsh winter conditions. It is attributable at first to the increase in temperature and its major control on the snow/rain partitioning. Yet, a magnitude effect, with less dependent extremes due to a decrease in intensity of precipitation, also exists. Finally, we show that our results are largely insensitive to the minimal modeling assumptions necessary to our data-based approach. This robustness makes it potentially suitable for various other studies in the field of geophysical extremes.

Description: The Cloud Imaging and Particle Size (CIPS) instrument on the Aeronomy of Ice in the Mesosphere (AIM) satellite provides an opportunity to study the longitudinal variation in polar mesospheric cloud (PMC). We examined the longitudinal variation in PMC albedo using 8 years (2007-2014) of observations from the CIPS instrument. The results show that the PMC albedo in the Southern Hemisphere (SH), especially in the latitude band of 80°S-85°S, is persistently low (~65% relative to the rest of the hemisphere) within 60°W to 150°W longitude. In the Northern Hemisphere (NH), however, PMC albedo is found to be relatively zonally asymmetry. Harmonic analyses shows that the persistent longitudinal variation in the SH PMC albedo is due to zonal wavenumbers 1 through 4 (WN1-WN4) processes with minima in the longitude range of 60°W-150°W. The influence of temperature and H 2 O on the longitudinal variation of the PMC albedo is discussed based on results obtained using a simple 0-D PMC model and temperature from the Microwave Limb Sounder (MLS) and the Sounding of the Atmosphere with Broadband Emission Radiometry (SABER) and H 2 O from MLS. The modeled region of low ice mass in the SH is generally consistent with that of low PMC albedo seen in CIPS. Tidal analyses using the SABER temperatures indicate that the non-migrating semidiurnal tides with modes of S0, W1 and E1 might be the main drivers of the persistent longitudinal variations of PMC albedo in the SH. Non-migrating tides are much weaker in the NH and consistent with the observed lack of longitudinal variability in PMC albedo.

Description: Approximately 63 million lightning flashes have been identified and analyzed from multiple years of Washington DC, northern Alabama, and northeast Colorado lightning mapping array (LMA) data using an open-source flash-clustering algorithm. LMA networks detect radiation produced by lightning breakdown processes, allowing for high resolution mapping of lightning flashes. Similar to other existing clustering algorithms, the algorithm described herein groups lightning-produced radiation sources by space and time to estimate total flash counts and information about each detected flash. Various flash characteristics and their sensitivity to detection efficiency are investigated to elucidate biases in the algorithm, detail detection efficiencies of various LMAs and guide future improvements. Furthermore, flash density values in each region are compared to corresponding satellite estimates. While total flash density values produced by the algorithm in Washington DC (~20 flashes km -2 yr -1 ) and Alabama (~35 flashes km -2 yr -1 ) are within 50% of satellite estimates, LMA-based estimates are approximately a factor of 3 larger (50 flashes km -2 yr -1 ) than satellite estimates in northeast Colorado. Accordingly, estimates of the ratio of in-cloud to cloud-to-ground flashes near the LMA network (~20) are approximately a factor of 3 larger than satellite estimates in Colorado. These large differences between estimates may be related to the distinct environment conducive to intense convection, low altitude flashes and unique charge structures in northeast Colorado.

Description: According to the high time-resolved spectra of two first and a subsequent return strokes and the following continuing current (CC) processes overlapped with M-components in three natural cloud-to-ground (CG) lightning, the correlation between the total intensity of ionic lines in the spectra and the corresponding amplitude of electric field change, and that between the total intensity of the spectra and the apparent diameter of the discharge channel have been investigated. Linear correlations have been found for the above two sets of parameters. The luminous properties along the channel show that the total intensity of ionic lines in the spectra for both the return stroke and M-components decreases with increasing height along the channel. The total intensity of the spectra and the apparent diameter for the return stroke also go down with increase of the height, while those for M-components do the reverse.

Description: An operational mitigation strategy for commercial aircraft impact on atmospheric composition, referred to as the turboprop replacement strategy (TRS) is described in this paper. The global air traffic between 2005 – 2011 was modelled with the TRS in which turbofan powered aircraft were replaced with nine chosen turboprop powered aircraft on all routes up to 1700 nautical miles (NM) in range. The results of this TRS double the global number of departures, as well as global mission distance, while global mission time grows by nearly a factor of three. However, the global mission fuel as well as the emissions of aviation CO 2 , H 2 O, and SO x remain approximately unchanged, and the total global aviation CO, hydrocarbons (HC), and NO x emissions are reduced by 79%, 21%, and 11% on average between 2005 and 2011. The TRS lowers the global mean cruise altitude of flights up to 1700 NM by ~2.7 km which leads to a significant decrease in global mission fuel burn, mission time, distance flown, and the aircraft emissions of CO 2 , CO, H 2 O, NO x , SO x , HC above 9.2 km. The replacement of turbofans with turboprops in regional fleets on a global scale leads to an overall reduction in levels of tropospheric O 3 at the current estimated mean cruise altitude near the tropopause where the radiative forcing of O 3 is strongest. Further, the replacement strategy results in a reduction of ground level aviation CO and NO x emissions by 33 and 29%, respectively between 2005 and 2011.

Description: Stratospheric final warming (SFW) in the Southern Hemisphere is examined in terms of their interannual variability and climatology using reanalysis data from January 1979 to March 2014. First it is shown from a two-dimensional transformed Eulerian mean (TEM) analysis that a time-integrated vertical component of Eliassen-Palm flux during the spring is significantly related with SFW date. To clarify the role of residual mean flow in the interannual variability of the SFW date, SFWs are categorized into early and late groups according to the SFW date and their differences are examined. Significant difference in potential temperature tendency is observed in the middle and lower stratosphere in early October. Their structure in the meridional cross section accords well with that of vertical potential temperature advection by the residual mean flow. Difference in heating rate by shortwave radiation is minor. These results suggest that the adiabatic heating associated with the residual mean flow largely affects polar stratospheric temperature during austral spring and SFW date. The analysis is extended to investigate the longitudinal structure by using a three-dimensional (3D) TEM theory. The significant difference in potential temperature tendency is mainly observed around the Weddell Sea at 10 hPa. Next, climatological 3D structure of a vertical component of the residual mean flow in association with SFW is examined in terms of the effect on the troposphere. The results suggest that a downward residual mean flow from the stratosphere penetrates into underlying troposphere over East Antarctica and partly influences tropospheric temperature there.