ALBERT

Description: [1]  A statistical algorithm was developed to estimate PM 2.5 concentrations over Europe based on a weather-type representation of the meteorology. We used modeled PM 2.5 concentrations as pseudo-observations, because of a lack of PM 2.5 speciated measurements over Europe, and included four meteorological variables. This algorithm was evaluated on the learning period (2000-2008) to test its ability to reproduce the pseudo-observed data set and then applied for two climatological scenarios (RCP4.5 and RCP8.5), one historical (1975-2004) and two future periods (2020-2049 and 2070-2099). In Italy, Poland, northern, eastern, and southeastern Europe, all future scenarios lead to decreases in PM 2.5 , whereas, in the Balkans, Benelux, the U.K., and northern France, they lead to increases in PM 2.5 . Considering each season separately shows stronger responses, which may vary for a given region and scenario. Decomposing the changes in PM 2.5 concentrations as the sum of inter-type and intra-type changes, and a residual term shows that: (1) the residual term is negligible, (2) inter-type changes affect more the regions along the Atlantic Ocean, (3) in most other regions, inter-type and intra-type changes are often on the same order of magnitude. The relationship between the atmospheric circulation and weather-types evolves, and therefore modifies the mean of meteorological variables and PM 2.5 concentrations. This algorithm offers a novel approach to investigate the effect of climate change on air quality, and can be applied to other pollutants, regions, and meteorological models. Furthermore, this approach can be applied using actual speciated PM 2.5 observations, if a sufficiently dense monitoring network were available.

Description: [1]  Monsoon droughts, especially on a decadal-to-centennial time scale, may have a profound impact on the populations of East Asia. Previous work has suggested that the East Asian summer monsoon (EASM) was synchronously strong across East Asia during the Medieval Climate Anomaly (MCA, 900-1300 AD); however, there is a dearth of studies addressing the issue of whether or not the EASM varied significantly during the entire duration of the MCA. Here we present results from a diverse range of proxy paleoclimatic records from the monsoonal and temperate Asian region in order to evaluate the occurrence of such short-time-scale variability within the MCA. Within the context of an overall strong EASM during the MCA, a weakening of the monsoon was detected in many of the records during the period 1000-1100 AD. Comparison of the timing of this event with variations of sea surface temperature (SST) of the Indian Ocean-western Pacific and with proxy records of solar activity reveals a significant co-variation, suggesting that the driver of the event may have resulted from changes in the Indian Ocean-western Pacific, related to changes in solar activity. To further address the issue of a terrestrial-oceanic linkage, we used the ECHO-G coupled climate model to simulate the variation of EASM precipitation over the last millennium. The model results suggest an interval of weak East Asian summer monsoon at 1000-1100 AD, and they also reveal a significant positive correlation with the SST of the Indian Ocean-western Pacific.

Description: [1]  The significance of non-isentropic irreversible mixing processes is diagnosed for idealized simulations of synoptic-scale baroclinic wave life-cycles along the subtropical jet stream, using a non-hydrostatic, anelastic, mesoscale model subject to a free-slip surface boundary condition. A variety of morphological features of mixing are identified such as a mesoscale columnar vortex associated with the onset of frontal fracture, episodic overturnings along the surface fronts, “wrinkling” of the tropopause and injection of tropospheric air into the stratosphere. The evolution of the degree of non-isentropic irreversible mixing is first analysed by computing the change of the “base” component of potential energy that cannot be converted into kinetic energy. The structure of the mixing activity is also diagnosed through inspection of spatiotemporal changes of entropy to demonstrate that the surface fronts are by far the most active regions of such activity. This activity is found to be primarily longitudinal, extending from the surface to the lower stratosphere, to form a three-dimensional spiral in the synoptic-scale cyclone and along the fronts. However, an exceptional region also exists along the warm front, where the structure becomes primarily transverse in the mature phase of frontal development in a model including an explicit representation of small-scale turbulence. In all simulations, the net transfer of mass and heat across the tropopause is from troposphere to stratosphere. The maximum transfer occurs when the observed climatological level of stratification contrast is assumed between stratosphere and troposphere. The same climatological choice leads to a minimum net irreversible mixing, which occurs primarily at Earth's surface.

Description: [1]  All chemical transport models require an estimation of the vertical distribution of smoke particles near the source. This study quantitatively examines the strengths and weaknesses of several fire products for characterizing plume buoyancy and injection heights in the North American boreal forest during 2004-2005. Observations from the Multi-angle Imaging SpectroRadiometer (MISR) show that 21% of smoke plumes are injected more than 500 m above the boundary layer (BL 500 ) and 8% exceed 2.5 km above ground level. Corresponding observations from the MODerate Resolution Imaging Spectroradiometer (MODIS) show that probability of injection above the BL 500 exceeds 60% for pixel-based fire radiative power (FRP p ) values above ~2500 MW. Increasing values of sub-pixel-retrieved fire area and temperature also correspond to higher injections, but only after removing fire pixels with a weak 11 µm fire signal and clustering. The probability of injection above the BL 500 reaches 50% when the sub-pixel radiant flux (FRP f flux) exceeds 20 kW/m 2 , highlighting its potential for estimating plume buoyancy. However, these data have limitations similar to FRP p , where the highest probability of injection corresponds to a small percentage of the dataset (5-18%), and many high-altitude injections occur with lower values. Examinations of individual smoke plumes highlight the importance of combining pixel-level and sub-pixel outputs, and show that plume injection is also sensitive to the fire pixel spatial distribution and meteorology. Therefore, an optimal method for predicting high-altitude injections will require some combination of injection climatology, FRP p , FRP f flux, and meteorology, but each variable's importance will depend on fire event characteristics.

Description: The climate sensitivity predicted in General Circulation Models (GCMs) can be sensitive to the treatment of the ice particle fall velocity. In this study, the mass weighted ice fall speed (V m ) and the number concentration ice fall speed (V n ) in mid-latitude cirrus clouds are computed from in-situ measurements of ice particle area and number concentration made by the 2-dimensional Stereo (2D-S) probe during the Small Particles In Cirrus (SPartICus) field campaign. For single-moment ice microphysical schemes, V m and the ice particle size distribution (PSD) effective diameter D e were parameterized in terms of cloud temperature (T) and ice water content (IWC). For two-moment schemes, V m and V n were related to D e and the mean maximum dimension¯D, respectively. For single-moment schemes, although the correlations of V m and D e with T were higher than the correlations of V m and D e with IWC, it is demonstrated that V m and D e are better predicted by using both T and IWC. The parameterization relating V m to T and IWC is compared with another scheme relating V m to T and IWC, with the latter based on Millimeter Cloud Radar (MMCR) measurements. Regarding two-moment ice microphysical schemes, a strong correlation was found between D e and V m and between¯D and V n owing to their similar weightings by ice particle mass and number concentration, respectively. Estimating V m from D e makes V m a function of IWC and projected area, realistically coupling V m with both the cloud microphysics and radiative properties.

Description: Humic-like substances (HULIS) are a complex group of relatively high molecular weight organic compounds which contribute considerably to the mass of organic carbon (OC) and influence the light-absorbing properties of aerosols. In this work, HULIS were investigated for the first time in the high-Arctic atmosphere, focusing on the chemical characterization and mass contribution of HULIS to the total suspended particle (TSP) mass using weekly aerosol samples collected at Station Nord, north east Greenland every 4 th week during 2010. Average HULIS-C concentration was 11 ng C m -3 during the darker months (November - April) and 4 ng C m -3 during the other months (May - October) with an annual mass concentration of 0.02 ± 0.01 µg m -3 . HULIS-C contributed to 3 - 16 % of WSOC whereas HULIS accounted for 0.7 - 4.1 % of TSP mass, with TSP typically below 1.0 µg m -3 . Concentrations of OC, water soluble organic carbon (WSOC), HULIS, selected HULIS functional groups (carboxylic acids, aromatic carboxylic acids and organosulfates) and levoglucosan overlapped with the typical Arctic haze pattern with elevated concentrations during winter - early spring. The aromatic carboxylic acid portion accounted for a larger share of total carboxylic acid of HULIS during the darker months (7%) compared to the brighter months (3%). The more abundant aromatic carboxylic acid functional groups and the moderate correlation between HULIS and levoglucosan concentrations during the darker months both indicate that biomass burning aerosols and thereby emissions of aromatic compounds could contribute to HULIS in the Arctic, especially during late winter. During the brighter months, relatively higher average molecular weight (AMW) of HULIS was observed.

Description: A Dust Aerosol Index (DAI) algorithm based on measurements in deep-blue (412 nm), blue (440 nm) and shortwave IR (2130 nm) wavelengths using MODerate resolution Imaging Spectro-radiometer (MODIS) observations has been developed. Contrary to some dust detection algorithms that use measurements at thermal IR bands, this algorithm takes advantage of the spectral dependence of Rayleigh scattering, surface reflectance, and dust absorption to detect airborne dust. The DAI images generated by this algorithm agree qualitatively with the location and extent of dust observed in MODIS true color images. Quantitatively, the dust index generated for hundreds of dust outbreaks observed between 2006 and 2013 were compared to Cloud Aerosol Lidar with Orthogonal Polarization (CALIOP) Vertical Feature Mask (VFM) product and the detections are found to be accurate at 70% over land and 82% over ocean. The Probability of Correct Detection (POCD) is 80% over land and 76% over ocean. The dust detections with DAI-based dust identification algorithm were also compared to five years of AERosol Robotic NETwork (AERONET) observations for thirteen stations with a wide range of geographical coverage. The average detection accuracy is ~70% whereas the POCD is ~67%. The performance of DAI-based dust detection against AERONET is slightly weaker than that against CALIOP VFM because of the limited number of matchups for some stations. For stations close to source region or coastal and island stations, the accuracy and POCD can be as high as ~85% and ~89%, respectively.

Description: Precipitation retrievals from space-borne Passive Microwave (PMW) radiometers are the backbone of modern satellite-based global precipitation datasets. The error characteristics in these individual retrievals directly affect the merged end products and applications, but have not been systematically studied. This paper focuses on extensive and systematic validation of PMW precipitation retrievals and quantification of their error characteristics. Retrievals from twelve PMW radiometers were evaluated and inter-compared at instantaneous scale (5 min) over continental United States. These precipitation-sensing radiometers include both imagers (TMI, AMSR-E, SSM/I, and SSMIS) and sounders (AMSU-B and MHS). A high-resolution ground radar-based dataset over the continental United States was used as the ground reference data. The high spatial and temporal resolution of the reference data allows collocation within 5 minutes and relatively more precise comparison with the satellite overpasses. Our results show that PMW sensor retrievals exhibit fairly systematic biases depending on season and precipitation intensity, with overestimates in summer at moderate to high precipitation rates and underestimates in winter at low and moderate precipitation rates. Retrievals from the microwave imagers have notably better performance than those from the sounders. The latter tend to have a narrower dynamic range, higher biases and random errors.

Description: China experienced severe haze pollution in January 2013. Here we have a detailed characterization of the sources and evolution mechanisms of this haze pollution with a focus on four haze episodes that occurred during 10-14 January in Beijing. The main source of data analyzed is from submicron aerosol measurements by an Aerodyne Aerosol Chemical Speciation Monitor. The average PM 1 mass concentration during the four haze episodes ranged from 144 – 300 µg m -3 , which was more than 10 times higher than that observed during clean periods (14 µg m -3 ). All submicron aerosol species showed substantial increases during haze episodes with sulfate being the largest. The large increase of sulfate was likely associated with aqueous-phase processing of sulfur dioxide (SO 2 ) under high humidity conditions along with an increase of particle acidity. Secondary inorganic species played enhanced roles in the haze formation as suggested by their elevated contributions during haze episodes. Positive matrix factorization analysis resolved six organic aerosol (OA) factors including three primary OA (POA) factors from traffic, cooking and coal combustion emissions, and three secondary OA (SOA) factors from local photochemical production, gas/particle partitioning, and regional transport. The OA compositions varied greatly among different haze episodes indicating their different sources and processes. Overall, SOA contributed 41 – 59% of OA with the rest being POA. Coal combustion OA (CCOA) was the largest primary source, on average accounting for 20- 32% of OA, and showed the most significant enhancement during haze episodes. A regional SOA (RSOA) was resolved for the first time which showed a pronounced peak only during the record-breaking haze episode (Ep3) on 12-13 January. The regional contributions estimated based on the steep evolution of air pollutants were found to play dominant roles for the formation of Ep3. The regional contribution on average accounted for 66% of PM 1 during the peak of Ep3 with sulfate, CCOA and RSOA being the largest fractions (〉 ~ 75%). Our results together suggest that stagnant meteorological conditions (low wind speed, high humidity, and shallow boundary layer), coal combustion, secondary production, and regional transport are four main factors driving the formation and evolution of haze pollution in Beijing during wintertime.

Description: Gravity waves are analyzed in radiosonde soundings taken during the TWP-ICE campaign. The properties of the inertia-gravity waves are analyzed in Part I, whereas Part II focuses on high-frequency gravity waves. Two groups of inertia-gravity waves are detected: group L ( L ong vertical wavelength) in the middle stratosphere during the suppressed monsoon period, and group S ( S hort vertical wavelength) in the lower stratosphere during the monsoon break period. Waves belonging to group L propagate to the south-east with a mean intrinsic period of 35 h, and have vertical and horizontal wavelengths of about 5-6 km and 3000-6000 km, respectively. Ray tracing calculations indicate that these waves originate from a deep convective region near Indonesia. Waves belonging to group S propagate to the south-south-east with an intrinsic period, vertical wavelength and horizontal wavelength of about 45 h, 2 km and 2000-4000 km, respectively. These waves appear to originate from convection in the region of New Guinea.

Description: High-frequency gravity waves are analyzed using radiosonde soundings taken during the Tropical Warm Pool - International Cloud Experiment (TWP-ICE) campaign. The intrinsic periods of these waves are estimated to be between 10 - 50 minutes. The high-frequency wave activity in the stratosphere, defined by mass-weighted variance of the vertical motion of the sonde, has a maximum following the afternoon local convection indicating that these waves are generated by local convection. The wave activity is the strongest in the lower stratosphere below 22 km and, during the suppressed monsoon period, is modulated with a 3 - 4 day period. The concentration of the wave activity in the lower stratosphere is consistent with the properties of the environment inwhich these waves propagate, whereas its 3 - 4 day modulation is explained by the variation of the convection activity in the TWP-ICE domain. For shallow convection, the wave activity has a weak tendency to increase as the rainfall intensity increases.The wave activity associated with deep convection, which typically occurs at high rainfall intensities, is larger and has more spread than that associated with shallow convection.

Description: This study investigates ozone changes and the individual impacts of transport and chemistry on those changes. We specifically examine (1) variation related to El Niño Southern Oscillation (ENSO), which is a dominant mode of interannual variation of tropospheric ozone, and (2) long-term change between the 2000s and 2100 s. During El Niño, the simulated ozone shows an increase (1 ppbv/K) over Indonesia, a decrease (2–10 ppbv/K) over the eastern Pacific in the tropical troposphere, and an increase (50 ppbv/K) over the eastern Pacific in the midlatitude lower stratosphere. These variations fundamentally agree with those observed by MLS/TES instruments. The model demonstrates that tropospheric chemistry has a strong impact on the variation over the eastern Pacific in the tropical lower troposphere, and that transport dominates the variation in the midlatitude lower stratosphere. Between the 2000s and 2100 s, the model predicts an increase in the global burden of stratospheric ozone (0.24%/decade) and a decrease in the global burden of tropospheric ozone (0.82%/decade). The increase in the stratospheric burden is controlled by stratospheric chemistry. Tropospheric chemistry reduces the tropospheric burden by 1.07%/decade. However, transport (i.e., stratosphere–troposphere exchange and tropospheric circulation) causes an increase in the burden (0.25%/decade). Additionally we test the sensitivity of ozone changes to increased horizontal resolution of the representation of atmospheric circulation and advection apart from any aspects of the nonlinearity of chemistry sensitivity to horizontal resolution. No marked difference is found in medium-resolution or high-resolution simulations, suggesting that the increased horizontal resolution of transport has a minor impact.

Description: [1]  Wuhan atmosphere radio exploration (WARE) radar is the first Mesosphere-Stratosphere-Troposphere (MST) radar to have become operative in the mainland of China and is dedicated to real-time atmospheric observations. Based on the WARE radar data collected for the period from September 2011 to February 2013, 2666 downward and 1735 upward inertia gravity waves (IGWs) are identified from three-dimensional (3-D) wind fields observed in the troposphere and subsequently analyzed in a statistical manner. Wave characteristics including intrinsic frequencies, vertical wavelengths, horizontal wavelengths, vertical wavenumber spectra, energy density spectra, and wave sources are investigated using a combination of the Lomb-Scargle spectral analysis, the quasi-monochromatic gravity waves model, and the hodograph method. Our results demonstrate that the characteristic parameters of upward and downward tropospheric IGWs are not significantly different. This results indicate that the tropospheric IGWs parameters are not directly correlated with propagation directions. Combining with the information of statistical 3D wind field and some climatic characteristics of Hubei Province, atmospheric moist convection will contribute most in summer, whereas jet/front systems will contribute most in winter. One may expect seasonal variations to be tied to the varying importance of these sources.

Description: Subgrid-scale interactions between turbulence and radiation are potentially important for accurately simulating marine low clouds in climate models. To better understand the impact of these interactions, the Weather Research and Forecasting (WRF) model is configured for large eddy simulation (LES) to study the stratocumulus-to-trade cumulus (Sc-to-Cu) transition. Using the GEWEX Atmospheric System Studies (GASS) composite Lagrangian transition case and the Atlantic Trade Wind Experiment (ATEX) case, it is shown that the lack of subgrid-scale turbulence-radiation interaction, as is the case in current generation climate models, accelerates the Sc-to-Cu transition. Our analysis suggests that subgrid-scale turbulence-radiation interactions in cloud-topped boundary layers contribute to stronger production of temperature variance, which in turn leads to stronger buoyancy production of turbulent kinetic energy and helps to maintain the Sc cover.

Description: The first of a new generation of microwave sounders was launched aboard the Suomi- National Polar-orbiting Partnership (S-NPP) satellite in October, 2011. The Advanced Technology Microwave Sounder (ATMS) combines the capabilities and channel sets of three predecessor sounders into a single package to provide information on the atmospheric vertical temperature and moisture profiles that are the most critical observations needed for numerical weather forecast models. Enhancements include size/mass/power approximately one third of the previous total, 3 new sounding channels, the first space-based, Nyquist-sampled cross-track microwave temperature soundings for improved fusion with infrared soundings, plus improved temperature control and reliability. This paper describes the ATMS characteristics vs. its predecessor, the Advanced Microwave Sounding Unit (AMSU), and presents the first comprehensive evaluation of key pre-launch and on-orbit performance parameters. Two years’ on-orbit performance show the ATMS has maintained very stable radiometric sensitivity, in agreement with pre-launch data, meeting requirements for all channels (with margins of ~40% for channels 1-15), and improvements over AMSU-A when processed for equivalent spatial resolution. The radiometric accuracy, determined by analysis from ground-test measurements, and using on-orbit instrument temperatures, also shows large margins relative to requirements (specified as 〈 1.0 K for channels, 1, 2, 16-22 and 〈 0.75 K for channels 3-15). A thorough evaluation of the performance of ATMS is especially important for this first Proto Flight Model (PFM) unit of what will eventually be a series of ATMS sensors providing operational sounding capability for the US and its international partners well into the next decade.

Description: Uncertainty in total ozone column (TOC) values is quantified for eight different databases through a direct comparison with ground-based data at three Spanish locations, the maximum uncertainty being about 10.5 DU. A long-term TOC series is constructed using the mentioned databases from 1950 to 2011 for nine locations in the Iberian Peninsula. The monthly TOC climatology in the nine locations is presented. An exhaustive analysis is performed of TOC series trends and their statistical significance in the periods 1950-2011, 1950-1984, and 1985-2011. A significant ozone reduction between 1950 and 2011 appears in the Iberian Peninsula with a strong reduction from the late 1970s to the mid 1990s and with more or less constant or slightly increasing levels in the last 17 year. These trends are recalculated taking into account of uncertainty in the TOC values of the series, with a decrease in the number of statistically significant trends emerging. The statistically significant trends in annual and in the averaged Iberian Peninsula series are usually still significant even considering the uncertainty. Finally, a study is carried out of the uncertainty caused by TOC uncertainty in total shortwave (SW) and erythemal ultraviolet (UVER) irradiances simulated under cloudless skies using a radiative transfer model.

Description: The effective radiative forcings (including rapid adjustments) and feedbacks associated with an instantaneous quadrupling of the pre-industrial CO 2 concentration and a counterbalancing reduction of the solar constant are investigated in the context of the Geoengineering Model Intercomparison Project. The forcing and feedback parameters of the net energy flux, as well as its different components at the top-of-atmosphere (TOA) and surface, were examined in ten Earth System Models to better understand the impact of solar radiation management on the energy budget. In spite of their very different nature, the feedback parameter and its components at the TOA and surface are almost identical for the two forcing mechanisms, not only in the global mean, but also in their geographical distributions. This conclusion holds for each of the individual models despite inter-model differences in how feedbacks affect the energy budget. This indicates that the climate sensitivity parameter is independent of the forcing (when measured as an effective radiative forcing). We also show the existence of a large contribution of the cloudy-sky component to the shortwave effective radiative forcing at the TOA suggesting rapid cloud adjustments to a change in solar irradiance. In addition, the models present significant diversity in the spatial distribution of the shortwave feedback parameter in cloudy regions, indicating persistent uncertainties in cloud feedback mechanisms.

Description: This study uses a regional fully coupled chemistry-transport model to assess changes in surface ozone over the summertime U.S. between present and a 2050 future time period at high spatial resolution (12 km grid spacing) under the SRES A2 climate and RCP8.5 anthropogenic precursor emission scenario. The impact of predicted changes in regional climate and globally enhanced ozone is estimated to increase surface ozone over most of the U.S; the 5 th - 95 th percentile range for daily 8-hour maximum surface ozone increases from 31-79 ppb to 30-87 ppb between the present and future time periods. The analysis of a set of meteorological drivers suggests that these mostly will add to increasing ozone, but the set of simulations conducted is targeted on understanding the competing effect of global versus local emission changes and does not allow separating the meteorological feedbacks from that due to enhanced global ozone. Statistically significant increases were found for future temperature, biogenic emissions and solar radiation. Stringent emission controls can counteract these likely positive feedbacks and if implemented as in RCP8.5, we estimate large reductions in surface ozone with the 5 th -95 th percentile reduced to 27-55 ppb. A comparison of the high-resolution projections to global model projections shows that the global model has a high positive bias in surface ozone compared to the regional model and compared to observations. On average, both the global and the regional model predict similar changes in ozone between the present and future time periods. However, on small spatial scales, the regional model shows pronounced differences between projections in urban and rural regimes that cannot be resolved at the coarse (2°x2°) resolution of the considered global model. This study confirms the key role of emission control strategies in future air quality projections and demonstrates the need for considering degradation of air quality with future climate change in emission policy making. It also illustrates the need for high resolution modeling when the objective is to address regional and local air quality or establish links to human health and society.

Description: For regional-scale investigations of greenhouse gas budgets the spatially explicit information from local emission sources is needed, which then can be compared with flux measurements. Here we present the first validation of a section of a spatially explicit CH 4 emission inventory of Switzerland. The validation was done for the agriculturally dominated Reuss valley using measurements from a low-flying aircraft (50–500 m above ground level). We distributed national emission estimates to a grid with 500 m cell size using available geostatistical data. Validation flux measurements were obtained using the eddy covariance (EC) technique and the boundary-layer budgeting (BLB) approach that only uses the mean concentrations of the same aircraft transects. Inventory estimates for the flux footprint of the aircraft measurements were lowest (median 0.40 g CH 4 m -2 s -1 ), and BLB fluxes were highest (1.02 g CH 4 m -2 s -1 ) for the Reuss valley, with EC fluxes in-between (0.62 g CH 4 m -2 s -1 ). Flux estimates from measurements and inventory are within the same order of magnitude, but measured fluxes were significantly larger than the inventory emission estimates. The differences are larger than the uncertainties associated with storage of manure, temperature dependence of emissions, diurnal cycle of enteric fermentation by cattle, and the limitations of the inventory that only covers ≥90% of all expected methane emissions. From this we deduce that it is not unlikely that the Swiss CH 4 emission inventory estimates are too low.

Description: In this study, the effect of uncertainties in the parameterization of ice microphysical processes and initial conditions on the variability of cirrus microphysical and radiative properties are investigated in a series of cloud system-resolving perturbed physics ensemble (PPE) and initial condition ensemble (ICE) simulations. Three cirrus cases representative of midlatitude, subtropical and tropical anvil cirrus are examined.It is found that the variability in cirrus properties induced by perturbing uncertain parameters in ice microphysics parameterizations outweighs the variability induced by perturbing the initial conditions in midlatitude and subtropical cirrus. However, in tropical anvil cirrus the variability spanned by the PPE and ICE simulations is on the same order of magnitude. In the examined cirrus cases, uncertainties in the parameterization of ice microphysical processes mainly affect the vertical distribution of cloud fraction and ice water content (IWC) as well as cloud thickness whereas, in most cases, the overall cirrus cloud cover is only marginally affected. In all cirrus cases, the top three uncertainties controlling the microphysical variability and radiative impact of cirrus clouds are the mode of ice nucleation, the number concentrations of ice nuclei available for heterogeneous freezing and the threshold size of the parameterized ice autoconversion process whereas uncertainties in ice fall speeds are of minor importance. Changes in the ice deposition coefficient induce only transient effects on the microphysical properties and radiative impacts of cirrus except in the case of very low ice deposition coefficients on the order of about 0.05. Similarly, changes in the number concentration of sulfate aerosols available for homogeneous freezing have virtually no effect on the microphysical properties and radiative impact of midlatitude and subtropical cirrus but a minor effect on tropical anvil cirrus.

Description: Atmospheric downward longwave radiation at the surface ( L d ) quantifies the atmospheric greenhouse effect. This study evaluated L d simulations from 44 general circulation models (GCMs) in the Coupled Model Intercomparison Project Phase 5 (CMIP5) with a comprehensive dataset of L d observations at 156 global-distributed sites from 1992 to 2005. Compared with the Baseline Surface Radiation Network (BSRN) data that is of the highest quality among the available L d datasets, CMIP5 GCM L d has a negligible bias, much better than CMIP3 GCMs, likely because of the improvement of low cloud simulations in CMIP5 models. However, the selection of validation data has an important impact on the evaluation results. The global mean L d inferred from different bias removing methods are nearly the same, approximately 341 W m -2 globally averaged from 1992 to 2005. CMIP5 GCMs showed that global L d increased at a rate of 1.54 W m -2 per decade (p 〈 0.01) from 1979 to 2005, which is consistent with available reanalyses. This good agreement in long-term trends of L d is likely because both reanalyses and CMIP5 models reproduced the observed warming and the associated increase of water vapor content in the lower atmosphere. However, CMIP5 GCMs are still poor in producing monthly anomalies of L d .

Description: The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) onboard Envisat measured limb emission spectra in the mid-infrared during 2002–2012. These measurements have been used to retrieve vertically resolved distributions of the six principal reactive nitrogen (NO y ) compounds (HNO 3 , NO 2 , NO, N 2 O 5 , ClONO 2 , and HNO 4 ) with global coverage and independent of illumination conditions. The obtained data set provides an unique climatological record of NO y in the middle atmosphere for a 10-year period. From these data, the contribution of NO y produced by energetic particle precipitation (EPP) has been discriminated from that produced by N 2 O oxidation using a tracer correlation method. For this purpose, co-located CH 4 and CO observations, also measured with MIPAS, have been analyzed along with NO y . The resulting EPP-NO y distributions, obtained in the vertical range from 20 to 70 km, allow to trace odd nitrogen polar winter descent from the mesosphere down to the middle and lower stratosphere, where it contributes to catalytic ozone destruction. Highest EPP-NO y concentrations of up to 1 ppmv are found in the winter mesosphere around solstice, decreasing continuously with time and towards lower altitudes. In spring, peak concentrations of a few ppbv are observed at 22–25 km, clearly demonstrating a regular EPP impact on the entire stratosphere. The inter-annual variation shows a clear solar cycle signal in consonance with variation of the geomagnetic activity level. A pronounced hemispheric asymmetry of the global EPP-NO y distribution is observed, with higher concentrations in the Southern hemisphere (SH) and stronger variability in the Northern hemisphere (NH). Polewards of 60 ∘ , EPP-NO y contributes to the winter stratospheric and lower mesospheric (20–70 km) NO y column by 10–40% in the SH and 1–30% in the NH. Smaller contributions of 0.1–1% are found in both hemispheres also at mid-latitudes (30 ∘  − − 60 ∘ ). This study provides the first assessment of EPP-NO y intrusions into the stratosphere based on globally available satellite data on a decadal scale.

Description: The important radiative properties of clouds such as cloud optical depth (COD) and droplet effective radii (R e ) are retrieved from the simultaneous measurements by ground based Multi-Filter Rotating Shadow band Radiometer (MFRSR) and Microwave Radiometric Profiler (MWRP), co-located at Mahabubnagar, a rain shadow region in southern Indian peninsula. Min and Harisson ’ s [1996] retrieval algorithm is used for the first time to derive monsoon cloud properties in India. COD and liquid water path (LWP) retrieved from two independent instruments of MFRSR and MWRP showed reasonably good correlation. During monsoon (July to Sept) and post-monsoon (Oct) months, the maximum probability of occurrence of COD for overcast sky is 20. The maximum probability of occurrence of LWP is 100 gm -2 for water clouds during monsoon months. While Oct showed maximum occurrence at a lower value of 50 gm -2 , where most of the times the cloud bases are above freezing level indicating mixed phase clouds. Maximum R e varied from 14-16 µm (10-12%) to 12 µm (9%) during monsoon to post-monsoon transition with very less probability of occurrence indicating the characteristic feature of this region. A case study showed that the mean R e from ground-based and aircraft measurements are 12.0 ± 3.7 µm and 8.14 ± 1.4 µm, respectively, indicating a fairly good agreement within the experimental constraints. Inter comparison of ground-based and Moderate Resolution Imaging Spectroradiometer (MODIS) -Terra and Aqua derived COD, LWP and R e over the observational site for overcast and warm clouds indicate that on an average, MODIS retrieved mean COD and LWP are under estimated, while mean R e is over estimated as compared to ground retrievals.

Description: ABSTRACT We analyzed 40-year datasets of daily average visibility (a proxy for surface aerosol concentration) and hourly precipitation at seven weather stations, including three stations located on the Taihang Mountains, during the summertime in northern China. There was no significant trend in summertime total precipitation at almost all stations. However, light rain decreased, whereas heavy rain increased as visibility decreased over the period studied. The decrease in light rain was seen in both orographic-forced shallow clouds and meso-scale stratiform clouds. The consistent trends in observed changes in visibility, precipitation, and orographic factor appear to be a testimony to the effects of aerosols. The potential impact of large-scale environmental factors, such as precipitable water, convective available potential energy, and vertical wind shear, on precipitation was investigated. No direct links were found. To validate our observational hypothesis about aerosol effects, Weather Research and Forecasting model simulations with spectral-bin microphysics at the cloud-resolving scale were conducted. Model results confirmed the role of aerosol indirect effects in reducing the light rain amount and frequency in the mountainous area for both orographic-forced shallow clouds and meso-scale stratiform clouds and in eliciting a different response in the neighboring plains. The opposite response of light rain to the increase in pollution when there is no terrain included in the model suggests that orography is likely a significant factor contributing to the opposite trends in light rain seen in mountainous and plain areas.

Description: Accurate estimation of the satellite-based global terrestrial latent heat flux ( LE ) at high spatial and temporal scales remains a major challenge. In this study, we introduce a Bayesian model averaging ( BMA ) method to improve satellite-based global terrestrial LE estimation by merging five process-based algorithms. These are the moderate resolution imaging spectroradiometer ( MODIS ) LE product algorithm, the revised remote-sensing-based Penman-Monteith LE algorithm, the Priestley-Taylor-based LE algorithm, the modified satellite-based Priestley-Taylor LE algorithm, and the semi-empirical Penman LE algorithm. We validated the BMA method using data for 2000-2009 and by comparison with a simple model averaging ( SA ) method and five process-based algorithms. Validation data were collected for 240 globally distributed eddy covariance ( EC ) tower sites provided by FLUXNET projects. The validation results demonstrate that the five process-based algorithms used have variable uncertainty and the BMA method enhances the daily LE estimates, with smaller root mean square errors ( RMSEs ) than the SA method and the individual algorithms driven by tower-specific meteorology and Modern Era Retrospective Analysis for Research and Applications ( MERRA ) meteorological data provided by the NASA Global Modeling and Assimilation Office ( GMAO ), respectively. The average RMSE for the BMA method driven by daily tower-specific meteorology decreased by more than 5 W/m 2 for crop and grass sites, and by more than 6 W/m 2 for forest, shrub and savanna sites. The average coefficients of determination ( R 2 ) increased by approximately 0.05 for most sites. To test the BMA method for regional mapping, we applied it for MODIS data and GMAO-MERRA meteorology to map annual global terrestrial LE averaged over 2001–2004 for spatial resolution of 0.05°. The BMA method provides a basis for generating a long-term global terrestrial LE product for characterizing global energy, hydrological and carbon cycles.

Description: Numerical simulations were carried out to model the propagation of an airwave from the fireball that passed over Chelyabinsk (Russia) on February 15, 2013. The airburst of the Chelyabinsk meteoroid occurred due to its catastrophic fragmentation in the atmosphere. Simulations of the space-time distribution of energy deposition during the airburst were done using a novel fragmentation model based on dimensionality considerations and analogy to the fission chain reaction in fissile materials. The observed two-peak height distribution of energy release was successfully reproduced assuming that the meteoroid consisted of two pieces having different effective strength. The main piece of about 97.5% of the meteoroid mass had a strength that varied from 0.3 to 4.9 MPa during its fragmentation, and the second piece of about 2.5% of the meteoroid mass had the strength of 10.5 MPa. The calculated average fragment masses of the meteoroid pieces by the end of their fragmentation are about 2.3 kg. To get an estimate of the airburst energy, observed values of the airwave arrival times to different populated localities were retrieved from video records available on the Internet. The calculated arrival times agree well with the observed values for all the localities. Energy deposition in the atmosphere obtained from observations of the airwave arrival times was found to be 460±60 kt in TNT equivalent. We also obtained an independent estimate for the deposited energy, kt TNT from detecting the air increment velocity due to the wave passage in Chelyabinsk. The increment velocity values were retrieved from video records which showed car exhausts just before and after the airwave arrival. Assuming that the energy of about 90 kt TNT was irradiated in the form of visible light and infrared radiation, as registered with optical sensors (Yeomans & Chodas, 2013), one can value the total energy release to be about 550 kt TNT which is in agreement with previous estimates from infrasound registration and from optical sensors data. The overpressure amplitude and its positive phase duration in the airwave that reached the city of Chelyabinsk were calculated to be about 2 kPa and 10 s accordingly.

Description: The western North Pacific subtropical high (WNPSH) in boreal summer shows a remarkable enhancement after the early 1980s. Whereas the sea surface temperature (SST) in the North Indian Ocean (NIO) and the equatorial eastern Pacific (EEP) had been noted to have remarkable local or remote effects on enhancing the WNPSH, the influence of the Atlantic SST, so far, is hardly explored. This article reports a new finding: enhanced relationship between the tropical Atlantic (TA)-SST and the WNPSH after the early 1980s. Regression study suggests that the warm TA-SST produced a zonally overturning circulation anomaly, with descending over the equatorial central Pacific and ascending over the tropical Atlantic/eastern Pacific. The anomalous descending over the equatorial central Pacific likely induced low-level anticyclonic anomaly to the west and therefore enhanced the WNPSH. One implication of this new finding is for predictability. The well-known “spring predictability barrier” (i.e., the influence of El Niño and Southern Oscillation (ENSO) falls dramatically during boreal spring) does not apply to the TA-SST/WNPSH relationship. The TA-SST shows consistently high correlation starting from boreal spring when the ENSO influence continues declining. The TA-SST extends the predictability of the WNPSH in boreal summer approximately one season earlier to boreal spring.

Description: As part of TIGERZ campaign, latitudinal variation of aerosol optical properties were analysed over Indo-Gangetic Plains (IGP) to central Himalayas during pre-monsoon of 2008 and 2009. Measurements of aerosol optical depth (AOD) were performed using AERONET Sunphotometer at four sites with different aerosol environments. The AOD increases from Nainital located in central Himalayas to Kanpur located in IGP region. Further, aerosol size varies spatially with dominance of coarse mode aerosols at Kanpur compared to fine mode aerosols dominated at Nainital. Spectral variation of single scattering albedo suggests that during pre-monsoon, dust is the dominant species in the IGP with exception of Pantnagar, where absorbing aerosols are dominant. The optical properties of aerosols are calculated and shortwave clear sky aerosol radiative forcing (ARF) is estimated. An insignificant difference is found in columnar ARF and columnar heating rate (HR) when vertical profiles of aerosols are included in radiative transfer models. Over Nainital, average ARF is estimated to be -7.61, -45.75 and 38.14 Wm -2 at top of atmosphere (TOA), surface (SUR) and in the atmosphere (ATM), respectively. Average ARF is less negative at Kanpur compared to Pantnagar and Bareilly with values -17.63, -73.06, and 55.43 Wm -2 at TOA, SUR, and ATM, respectively. ARF shows positive gradient from the highlands to the IGP sites; larger TOA and SUR cooling were observed at the three sites compared to the highland site. This translates into large columnar HR with estimated average values as 1.07, 1.41, 1.58, and 1.56 Kday -1 for Nainital, Pantnagar, Bareilly and Kanpur, respectively.

Description: Large uncertainty in the direct radiative forcing of black carbon (BC) exists, with published estimates ranging from 0.25 to 0.9 W m -2 . A significant source of this uncertainty relates to the vertical distribution of BC, particularly relative to cloud layers. We first compare the vertical distribution of BC in CMIP5 models to aircraft measurements and find that models tend to overestimate upper tropospheric/lower stratospheric (UT/LS) BC, particularly over the central Pacific from HIPPO1. However, CMIP5 generally underestimates Arctic BC from the ARCTAS campaign, implying a geographically dependent bias. Factors controlling the vertical distribution of BC in CMIP5 models, such as wet and dry deposition, precipitation, and convective mass flux (MC), are subsequently investigated. We also perform a series of sensitivity experiments with the Community Atmosphere Model version 5 (CAM5), including prescribed meteorology, enhanced vertical resolution, and altered convective wet scavenging efficiency and deep convection. We find that convective mass flux has opposing effects on the amount of black carbon in the atmosphere. More MC is associated with more convective precipitation, enhanced wet removal, and less BC below 500 hPa. However, more MC, particularly above 500 hPa, yields more BC aloft due to enhanced convective lofting. These relationships-particularly MC versus BC below 500 hPa-are generally stronger in the tropics. Compared to the Modern-Era Retrospective Analysis for Research (MERRA), most CMIP5 models overestimate MC, with all models overestimating MC above 500 hPa. Our results suggest excessive convective transport is one of the reasons for CMIP5 overestimation of UT/LS BC.

Description: Oceanic tsunami waves couple with atmospheric gravity waves, as previously observed through ionospheric and airglow perturbations. Aerodynamic velocities and density variations are computed from GOCE accelerometer and thruster data during Tohoku-Oki tsunami propagation. High frequency perturbations of these parameters are observed during three expected crossings of the tsunami generated gravity waves by the GOCE satellite. From theoretical relations between air density, and vertical and horizontal velocities inside the gravity wave, we demonstrate that the measured perturbations are consistent with a gravity wave generated by the tsunami, and provide a way to estimatethe propagation azimuth of the gravity wave. Moreover, because GOCE measurements can constrain the wave polarisation, a marker (noted C 3 ) of any gravity wave crossing by the GOCE satellite is constructed from correlation coefficients between the observed atmospheric state parameters. These observations validate a new observation tool of thermospheric gravity waves generated by tsunamis above the open ocean.

Description: Chemistry climate models (CCMs) are used to project future evolution of stratospheric ozone as concentrations of ozone-depleting substances (ODSs) decrease and GHGs increase, cooling the stratosphere. CCM projections exhibit many common features, but also a broad range of values for quantities such as year of ozone-return-to-1980 and global ozone level at the end of the 21 st century. Multiple linear regression is applied to each of fourteen CCMs to separate ozone response to ODS concentration change from that due to climate change. We show that the sensitivity of lower stratospheric ozone to chlorine change ΔO 3 /ΔCl y is a near linear function of partitioning of total inorganic chlorine (Cl y ) into its reservoirs; both Cl y and its partitioning are largely controlled by lower stratospheric transport. CCMs with best performance on transport diagnostics agree with observations for chlorine reservoirs and produce similar ozone responses to chlorine change. After 2035 differences in ΔO 3 /ΔCl y contribute little to the spread in CCM projections as the anthropogenic contribution to Cl y becomes unimportant. Differences among upper stratospheric ozone increases due to temperature decreases are explained by differences in ozone sensitivity to temperature change ΔO 3 /ΔT due to different contributions from various ozone loss processes, each with its own temperature dependence. Ozone decrease in the tropical lower stratosphere caused by a projected speed-up in the Brewer-Dobson circulation may or may not be balanced by ozone increases in the middle and high latitude lower stratosphere and upper troposphere. This balance, or lack thereof, contributes most to the spread in late 21 st century projections.

Description: LIRIC (LIdar-Radiometer Inversion Code) is applied to combined lidar and sun photometer data from Granada EARLINET and AERONET station corresponding to different case studies. The main aim of this analysis is to evaluate the stability of LIRIC output volume concentration profiles for different aerosol types, aerosol loadings and vertical distribution of the atmospheric aerosols. For this purpose, in a first part, three case studies corresponding to different atmospheric situations are analysed to study the influence of the user-defined input parameters in LIRIC when varied in a reasonable range. Results of this study evidence the capabilities of LIRIC to retrieve vertical profiles of microphysical properties during daytime by combination of the lidar and the sun photometer systems in an automatic and self-consistent way. However, spurious values may be obtained in the lidar incomplete overlap region depending on the structure of the aerosol layers. In a second part, the use of a second sun photometer located in Cerro Poyos, in the same atmospheric column as Granada but at higher altitude, allowed us to obtain LIRIC retrievals from two different altitudes with independent sun photometer measurements in order to check the self-consistency and robustness of the method. Retrievals at both levels are compared, providing very good agreement (differences below 5 µm 3 /cm 3 ) in those cases with the same aerosol type in the whole atmospheric column. However, some assumptions such as the height-independency of parameters (sphericity, size distribution or refractive index, among others) need to be carefully reviewed for those cases with presence of aerosol layers corresponding to different types of atmospheric aerosols.

Description: In their seminal lightning studies using streak cameras, Schonland et al. [Progressive lightning, 6, Proc. Roy. Soc. (London), A168, 455-469, 1938] identified four negative stepped leader events that they term “β 2 ”, a “rather rare variant of the type β leader”, and in it “the second and slower stage of the leader is associated with the appearance of one or more fast dart streamers, which travel rapidly down from the cloud along the previously formed track and cease when they have caught up with the slower leader-tip”. Seven negative downward leaders that agreed with the description given by Schonland et al. for type β 2 .were recorded in Tucson, Arizona, USA, and in São José dos Campos, São Paulo, Brazil. All cases were recorded by a high-speed camera operating at 4000 frames per second and electric field changes were measured for three of them. Their “dart streamers” had speeds between 10 6 and 10 7  m s -1 , compatible with previous observations of recoil leaders (RLs). Also, during the development of the three cases with correlated electric field changes, it was possible to identify sequences of microsecond-scale pulses preceding the propagation of a “dart streamer” in the channel. It is proposed that the luminous process that occurs during the development of a type β 2 stepped leader is the visible manifestation of one or more RLs that begin inside the cloud and connect to the in-cloud, positive portion of the bipolar, bidirectional leader, and then travel downward to the lower end of the negative stepped leader path.

Description: Two global Level 2 SST products are generated at NOAA from the SNPP VIIRS sensor data records (L1) with two independent processing systems, the Joint Polar Satellite System (JPSS) Interface Data Processing Segment (IDPS), and the NOAA heritage Advanced Clear Sky Processor for Oceans (ACSPO). The two systems use different SST retrieval and cloud masking algorithms. Validation against in situ and L4 analyses has shown suboptimal performance of the IDPS product. In this context, existing operational and proposed SST algorithms have been evaluated for their potential implementation in IDPS. This paper documents the evaluation methodology and results. The performance of SST retrievals is characterized with bias and standard deviation with respect to in situ SSTs, and sensitivity to true SST. Given three retrieval metrics, all being variable in space and with observational conditions, an additional integral metric is needed to evaluate the overall performance of SST algorithms. Therefore, we introduce the Quality Retrieval Domain (QRD) as a part of the global ocean, where the retrieval characteristics meet predefined specifications. Based on the QRDs analyses for all tested algorithms over a representative range of specifications for accuracy, precision, and sensitivity, we have selected the algorithms developed at the EUMETSAT Ocean and Sea Ice Satellite Application Facility (OSI-SAF) for implementation in IDPS and ACSPO. Testing the OSI-SAF algorithms with ACSPO and IDPS products shows the improved consistency between VIIRS SST and Reynolds L4 daily analysis. Further improvement of the IDPS SST product requires adjustment of the VIIRS Cloud and Ice Masks.

Description: Major Stratospheric Sudden Warmings (SSWs) are characterized by a reversal of the zonal mean zonal wind and an anomalous warming in the polar stratosphere that proceeds downwards to the lower stratosphere. In the tropical stratosphere, a downward propagating cooling is observed. However, the strong modulation of tropical winds and temperatures by the Quasi-biennial Oscillation (QBO) renders accurate characterization of the tropical response to SSWs challenging. A novel metric based on temperature variations relative to the central date of the SSW using ERA-Interim data is presented. It filters most of the temperature structure related to the phase of the QBO and provides proper characterization of the SSW cooling amplitude and downward propagation tropical signal. Using this new metric, a large SSW-related cooling is detected in the tropical upper stratosphere that occurs almost simultaneously with the polar cap warming. The tropical cooling weakens as it propagates downwards, reaching the lower stratosphere ina few days. Substantial differences are found in the response to SSWs depending on the QBO phase. Similar to what is observed in the polar stratosphere, tropical SSW-associated temperatures persist longer during the west QBO phase at levels above about 40 hPa, suggesting that the signal is mainly controlled by changes in the residual mean meridional circulation associated with SSWs. Conversely, in the lower stratosphere, around 50–70 hPa, enhanced cooling occurs only during QBO east phase. This behavior seems to be driven by anomalous subtropical wave breaking related to changes in the zero-wind line position with the QBO phase.

Description: Previous studies have suggested that the boreal spring Arctic Oscillation (AO) could exert a significant influence on the outbreak of El Niño–Southern Oscillation (ENSO) during the following winter. This study further reveals that the influence of the spring AO on the subsequent ENSO is asymmetric. When the spring AO is in its high phase, significant El Niño-like SST warming anomalies are observed over the tropical central-eastern Pacific in the following winter. However, when the spring AO is in its low phase, negative SST anomalies over the tropical central-eastern Pacific are weak and statistically insignificant. This asymmetric influence is attributed to the asymmetric features of both the atmospheric circulation anomalies in spring and atmospheric heating anomalies over the subtropical North Pacific from spring to summer. For the high AO phase composite, the anomalous cyclonic circulation over the subtropical western North Pacific and the related westerly wind anomalies to its south over the tropical western Pacific are strong and significant in spring. The tropical zonal wind anomalies would trigger ENSO events via the excitation of an eastward-propagating Kelvin wave. Meanwhile, the atmospheric heating anomalies over the subtropical North Pacific play an important role in sustaining the westerly wind over the tropical western Pacific from spring to summer. In contrast, the counterparts in the low AO phase composite are weak and statistically insignificant. Our results indicate that the phase of spring AO should be taken into account when using spring AO as a predictor for ENSO.

Description: Dust transport to the tropical/subtropical northwestern Pacific over the past 600 kyr was investigated using radiogenic isotopes ( 87 Sr/ 86 Sr and ε Nd ), together with the clay mineral composition, of eolian dust preserved in a sediment core obtained from the Philippine Sea (12°30′N, 134°60′E). These data revealed the influence of two prevailing dust sources, namely, the Asian deserts and nearby volcanic arcs (e.g., the Luzon Arc), with average contributions of around 70% and 30%, respectively, from each. The clay mineral composition of the core resembled dust from the central Asian deserts (CADs; e.g., the Taklimakan Desert) as in the North Central Pacific, but published aerosol data collected near the study site during winter/spring has the mineralogical signature of dust originating from the East Asian deserts (EADs). These data indicate that the relative contribution of EAD dust increases with the northeasterly surface winds associated with the East Asian Winter Monsoon (EAWM) during winter/spring, but the Prevailing Westerlies and Trade Winds that carry dust from the CADs is the dominant transport agent in the overall dust budget of the study site. The results of this study contradict the prevailing view that direct dust transport by the EAWM winds in spring dominates the annual flux of eolian dust in the northwest Pacific.

Description: Located on the Tibetan Plateau, the source region of Yellow River has experienced remarkable climate change over past a few decades, which affects the regional ecosystem, agricultural development and water availability. In this paper, high resolution RegCM3 driven by ECHAM5 is applied to generate both control climate for 1980–2000 and regional climate projections for the 21 st century (2010–2098) under the IPCC A1B emission scenario. For control climate, RegCM3 can well reproduce the spatial patterns of precipitation and surface air temperature with more detailed representation of fine scale topography. Wet and cold biases are produced in the simulation, but overall improvement by RegCM3 is evident compared to the driving GCM of ECHAM5. In the future projection, the model demonstrates significant warming over the whole analysis domain. Precipitation on the other hand shows mixed signals of reduction and increase over simulation domain, while the areas of precipitation reduction extends with increasing integration time and finally covers most parts of the domain at the end of 21 st century. As projection time increases, high altitude region will experience more precipitation reduction in summer and less reduction or even increase in winter. The winter warming at high elevation area gets more evident than that at low elevation area, which may be due to the snow feedback. Analyzing the change of probability distributions of surface climate, it can be concluded that the frequency of heavy precipitation in winter tends to increase with time indicating more extreme precipitation events in the future. The spectrum of temperature PDFs moves towards higher end.

Description: The dual-carbon isotope signatures and optical properties of carbonaceous aerosols have been investigated simultaneously for the first time in the South Asian outflow during an intensive campaign at the Maldives Climate Observatory on Hanimaadhoo (MCOH) (February-March 2012). As one component of the Cloud Aerosol Radiative Forcing Dynamics Experiment (CARDEX), this paper reports on the sources and the atmospheric processing of elemental carbon (EC) and water-soluble organic carbon (WSOC) as examined by a dual carbon isotope approach. The radiocarbon (Δ 14 C) data show that WSOC has a significantly higher biomass/biogenic contribution (86 ± 5%) compared to EC (59 ± 4%). The more 13 C-enriched signature of MCOH-WSOC (−20.8 ± 0.7‰) compared to MCOH-EC (−25.8 ± 0.3‰) and megacity Delhi WSOC (−24.1 ± 0.9‰) suggests that WSOC is significantly more affected by aging during long-range transport than EC. The δ 13 C-Δ 14 C signal suggests that the wintertime WSOC intercepted over the Indian Ocean largely represents aged primary biomass-burning aerosols. Since light-absorbing organic carbon aerosols (‘Brown Carbon’, BrC) have recently been identified as potential contributors to positive radiative forcing, optical properties of WSOC were also investigated. The mass absorption cross section of WSOC (MAC 365 ) was 0.5 ± 0.2 m 2 g −1 which is lower than what has been observed at near-source sites, indicating a net decrease of WSOC light-absorption character during long-range transport. Near-surface WSOC at MCOH accounted for ~1% of the total direct solar absorbance relative to EC, which is lower than the BrC absorption inferred from solar spectral observations of ambient aerosols, suggesting that a significant portion of BrC might be included in the water-insoluble portion of organic aerosols.

Description: This study demonstrates that absorbed solar radiation (ASR) at the top of the atmosphere in early summer (May–July) plays a precursory role in determining the Arctic sea ice concentration (SIC) in late summer (August–October). The monthly ASR anomalies are obtained over the Arctic Ocean (65°N–90°N) from the Clouds and the Earth's Radiant Energy System during 2000–2013. The ASR changes primarily with cloud variation. We found that the ASR anomaly in early summer is significantly correlated with the SIC anomaly in late summer (correlation coefficient, r  ≈ −0.8 with a lag of 1 to 4 months). The region exhibiting high (low) ASR anomalies and low (high) SIC anomalies varies yearly. The possible reason is that the solar heat input to ice is most effectively affected by the cloud shielding effect under the maximum TOA solar radiation in June and amplified by the ice-albedo feedback. This intimate delayed ASR-SIC relationship is not represented in most of current climate models. Rather, the models tend to over-emphasize internal sea ice processes in summer.

Description: ABSTRACT The high temporal resolution measurements of δ D, δ 18 O and deuterium excess ( d ) of atmospheric water vapor provide an improved understanding of atmospheric and eco-hydrological processes at ecosystem to global scales. In this study, δD, δ 18 O and d of water vapor and their flux ratios were continuously measured from May to September 2012 using an in situ technique above an arid artificial oasis in the Heihe River Basin, which has a typical continental arid climate. The monthly δ D and δ 18 O increased slowly and then decreased, whereas the monthly d showed a steady decrease. δ D, δ 18 O and d exhibited a marked diurnal cycle, indicating the influence of the entrainment, local evapotranspiration (ET) and dewfall. The departures of δ D, δ 18 O and d from equilibrium prediction were significantly correlated with rain amount, relative humidity (RH) and air temperature (T). The “amount effect” was observed during one precipitation event. δ D and δ 18 O were log linear-dependent on water vapor mixing ratio with respective R 2 of 17% and 14% whereas d was significantly correlated with local RH and T, suggesting the less influence of air mass advection and more important contribution of the local source of moisture to atmospheric water vapor. Throughout the experiment, the local ET acted to increase δ D and δ 18 O, with isofluxes of 102.5 and 23.50 mmol m −2  s −1 ‰, respectively. However, the dominated effect of entrainment still decreased δ D and δ 18 O by 10.1 and 2.24‰, respectively. Both of the local ET and entrainment exerted a positive forcing on the diurnal variability in d .

Description: The indirect effect of aircraft soot on cirrus clouds is subject to large uncertainties due to uncertainty in the effectiveness of aircraft soot acting as heterogeneous ice nuclei (IN) and the complexity caused by background ice nucleation which introduces two major competing ice nucleation mechanisms: homogeneous freezing that generally produces more abundant ice particles and heterogeneous nucleation that generally produces fewer ice particles. In this paper, we used the coupled CAM5/IMPACT model to estimate the climate impacts of aircraft soot acting as IN in large-scale cirrus clouds. We assume that only the aircraft soot particles that are preactivated in persistent contrail cirrus clouds are efficient IN. Further, we assume these particles lose their ability to act as efficient IN when they become coated with 3 monolayers of sulfate. We varied the background number concentration of sulfate aerosols allowed to act as homogeneous ice nucleation sites as well as the dust concentrations that act as heterogeneous ice nuclei to examine the sensitivity of the forcing by aircraft soot to the background atmosphere. The global average effect can range from a high negative (cooling) rate, −0.35 W m −2 , for the high sulfate/low dust case to a positive (warming) rate, +0.09 W m −2 , for the low sulfate/low dust case (default CAM5 set-up) when approximately 0.6% of total aviation soot act as IN. The net negative forcing is caused by the addition of IN to a background atmosphere that is dominated by homogeneous nucleation (mainly in the tropic Indian Ocean, Central America and North Atlantic Ocean). The forcings can be all positive, about +0.11 to +0.21 W m −2 , when the background atmosphere is dominated by pure heterogeneous ice nucleation.

Description: The Palmer Drought Severity Index (PDSI) has been widely used to evaluate drought conditions since it was developed in 1965. In the original formulation of the PDSI, potential evapotranspiration (PET) was estimated using the Thornthwaite equation. This study evaluates how using more physically-based approaches for estimating PET influences the depiction of drought conditions over the U.S. Great Plains from 1980 to 2012. Both the Penman-Monteith equation and the two-source PET model are compared to the original Thornthwaite-based PDSI. The differences in PET between the three methods are much larger than the resulting differences in the PDSI. Results show that the original PDSI has a stronger drying trend than versions of PDSI that use more physically-based methods of estimating PET. Spatially, all three versions of the PDSI show similar distributions of drying and wetting trends, however there are significant regional variations that appear to be associated with land cover. PDSI and observed soil moisture in the top 1-m are moderately correlated (correlation coefficient is ~0.5) over the U.S. Great Plains, except in Texas (correlation coefficient is ~0.3). Although all three approaches result in a similar area-averaged PDSI for the U.S. Great Plains, there are large differences in the area affected by drought, especially during extreme drought events.

Description: Variability in the chemistry of the upper stratosphere / lower mesosphere (USLM) region has been analyzed focusing on high latitudes during the boreal winter 2009 characterized by the strong sudden stratospheric warming (SSW) on 24 January. Data from Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) aboard ENVISAT and the Microwave Limb Sounder (MLS) on Aura have been used to exemplify these changes. Record high (low) values of O 3 and ClO (temperature and HCl) for the winters of 2005-2012, coupled with a simultaneous enhancement of ClONO 2 , have been observed in February 2009. This suggests that the very low temperatures favor a more effective ozone production and a greater O 3 /O ratio. The latter is the main factor controlling active chlorine partitioning. Increases of ClO lead to high ClONO 2 concentrations in the upper stratosphere at high latitudes, where its photodissociation rate is smaller. Since this increase of ClONO 2 happens at the expense of HCl, the region of high ClONO 2 coincides roughly with the region of low HCl. Although this period was characterized by an elevated stratopause event, the investigated region was not influenced by the descent of mesospheric air rich in NO x . Some limited enhancements in NO x at ~1 hPa occurred at latitudes greater than 80° N after about 20 February but they became consistent only in March. Intrusion of mid-latitude air mostly occurred between the SSW and early February. Then, the sum of VMRs of ClONO 2  + ClO + HCl remained approximately constant and close to the values of the other years. In contrast, it was up to 0.2 ppbv lower during the SSW period. These atypical chemical conditions occurred also in February 2006, but 2009 stands out for its long-lasting effects, which persisted until late March.

Description: This paper presents a simple method for representing upward capillary fluxes from shallow groundwater into the unsaturated soil column of the large-scale hydrological models generally used at low resolution in global climate models. The groundwater scheme implemented in the Total Runoff Integrated Pathways (TRIP) river routing model in a previous study is coupled with the Interaction between Soil Biosphere Atmosphere (ISBA) land surface model. In this coupling, the simulated water table depth acts as the lower boundary condition for the soil moisture diffusive equation. An original parameterization accounting for the sub-grid topography inside each grid cell is proposed in order to compute this fully-coupled soil lower boundary condition. The impact of this coupling on the simulated water budget is evaluated over France for the 1989–2009 period. Simulations are performed at high (1/12°) and low (0.5°) resolutions. Upward capillary fluxes induce a decrease in the simulated recharge from ISBA to the aquifers and contributes to an enhancement of the soil moisture memory. The simulated water table depths are then lowered, which induces a slight decrease in the simulated mean annual river discharges. These differences do not affect the comparison with observations. As a consequence, the simulated river discharges and water table heads compare still well with observations for the two soil bottom condition (free-drain or fully-coupled). It confirms the suitability of the coupling parameterization using sub-grid spatial variability of topography. Compared to a free-drain experiment, upward capillary fluxes at the bottom of the soil increase the mean annual evapotranspiration simulated over the aquifer domain by 3.12% and 1.54% at high and low resolutions, respectively. This increase can locally reach 50% and 30% respectively.

Description: High-resolution, global quantification of fossil fuel CO 2 emissions is emerging as a critical need in carbon cycle science and climate policy. We build upon a previously developed fossil fuel data assimilation system (FFDAS) for estimating global high-resolution fossil fuel CO 2 emissions. We have improved the underlying observationally based data sources, expanded the approach through treatment of separate emitting sectors including a new pointwise database of global power plants, and extended the results to cover a 1997 to 2010 time series at a spatial resolution of 0.1°. Long-term trend analysis of the resulting global emissions shows subnational spatial structure in large active economies such as the United States, China, and India. These three countries, in particular, show different long-term trends and exploration of the trends in nighttime lights, and population reveal a decoupling of population and emissions at the subnational level. Analysis of shorter-term variations reveals the impact of the 2008–2009 global financial crisis with widespread negative emission anomalies across the U.S. and Europe. We have used a center of mass (CM) calculation as a compact metric to express the time evolution of spatial patterns in fossil fuel CO 2 emissions. The global emission CM has moved toward the east and somewhat south between 1997 and 2010, driven by the increase in emissions in China and South Asia over this time period. Analysis at the level of individual countries reveals per capita CO 2 emission migration in both Russia and India. The per capita emission CM holds potential as a way to succinctly analyze subnational shifts in carbon intensity over time. Uncertainties are generally lower than the previous version of FFDAS due mainly to an improved nightlight data set.

Description: This study investigates changes in temporal trends and spatial patterns of precipitation in Beijing over the last six decades. These changes are discussed in the context of rapid urbanization and the growing imbalance between water supply and demand in Beijing. We observed significant decreases in precipitation amounts from 1950 to 2012, with the annual precipitation decreasing by 32% at a decadal rate of 28.5 mm. In particular, precipitation decrease is more pronounced in the summer and warm seasons when water use is at its seasonal peak. We further analyzed hourly precipitation data from 43 rain gauges between 1980 and 2012 to examine the spatio-temporal characteristics of both precipitation amount and intensity across six distinct sub-regions in Beijing. No significant spatial variations in precipitation changes were identified, but slightly greater amounts of precipitation were noted in the urban areas (plains) than in the surrounding suburbs (mountains), due to the effect of urbanization and topography. Precipitation intensity has increased substantially, especially at the hourly duration, as evidenced by the more frequent occurrence of extreme storms. The observed decreased water availability and the increase in extreme weather events require more integrated water management, particularly given the expectation of a warmer and more variable climate, the continued rapid growth of the Beijing metropolis, and the intensifying conflict between water supply and demand.

Description: Filter-based particle samples were simultaneously collected at 14 sites across 6 regions of China during the summer of 2012. These filters were analyzed for secondary organic aerosol (SOA) tracers from biogenic precursors (isoprene, monoterpenes and β-caryophyllene) and anthropogenic aromatics. The sum of all SOA tracers ranged from 29.9 to 371 ng m −3 with the majority from isoprene (123 ± 78.8 ng m −3 ), followed by monoterpenes (10.5 ± 6.64 ng m −3 ), β-caryophyllene (5.07 ± 3.99 ng m −3 ) and aromatics (2.90 ± 1.52 ng m −3 ). The highest levels of biogenic SOA tracers were observed in East China, whereas the highest concentrations of the aromatic SOA tracer, 2,3-dihydroxy-4-oxopentanoic acid (DHOPA), occurred in North China. All biogenic SOA tracers exhibited positive correlations with temperature, most likely resulting from enhanced biogenic volatile organic compounds (BVOCs) emissions and photochemistry in high-temperature regions. Among the isoprene SOA tracers, the low-NOx products 2-methyltetrols were the largest by mass concentration. However, at certain urban sites, the contribution of the high-NOx product 2-methylglyceric acid was significantly higher, implying a greater influence of NOx on isoprene SOA formation in urban areas. For the monoterpene SOA tracers, the ratio of the first-generation products (cis-pinonic acid plus pinic acid) to the high-generation product (3-methyl-1,2,3-butanetricarboxylic acid) exhibited a negative correlation with the amount of high-generation products, indicating that this ratio could serve as an indicator of the aging of monoterpene SOA. The ratio ranged from 0.89 to 21.0, with an average of 7.00 ± 6.02, among the observation sites, suggesting that monoterpene SOA was generally fresh over China during the summer. As a typical anthropogenic SOA tracer, DHOPA exhibited higher levels at urban sites than at remote sites. These SOA tracers were further used to attribute SOA origins via the SOA-tracer method. The total concentrations of secondary organic carbon (SOC) and SOA were estimated to be in the range of 0.37 to 2.47 μgC m −3 and 0.81 to 5.44 µg m −3 , respectively, with the highest levels observed in the eastern regions of China. Isoprene (46 ± 14%) and aromatics (27 ± 8%) were the two major contributors to SOC in every region. In North China, aromatics were the largest SOA contributor. Our ground-based observations suggest that anthropogenic aromatics are important SOA precursors in China.

Description: Using 33-year ERAI reanalysis in the months of August and September we found that more than half of the low-level, moist vortices (called wet vortices) originating from south of the African easterly jet merged with a shallow, dry vortex from the north after leaving the West African coast. A dry vortex involved with the merger process is referred to as a D-vortex and the process is referred to as a D-vortex merger. Dry vortices influenced by more intense African easterly waves moved southwestward and had a greater potential to serve as D-vortices in the merger process. The D-vortex merger occurred in the pre-depression stage of 70% of tropical cyclones (TCs) that formed in the Atlantic main development region, and in 55% of non-developing systems. Further analysis showed that developing systems with the D-vortex merger (DM) were statistically dominated by a more intense wet vortex whose 500-hPa relative humidity was also significantly higher, while non-developing systems with the D-vortex merger (NM) were dominated by a more intense dry vortex. The average intensity of wet vortices for DM was more intense than that for NM, significant at a 95% confidence level. Moreover, warmer Saharan air was observed for DM than NM. While TC genesis is largely controlled by the large-scale environment over ocean, differences in vortex characteristics and environment over northwestern Africa between DM and NM could potentially help predict whether a tropical system associated with the D-vortex merger will ultimately evolve into an Atlantic TC.

Description: ABSTRACT Episodic wintertime particle pollution by ammonium nitrate is an important air quality concern across the Midwest U.S. Understanding and accurately forecasting PM 2.5 episodes is complicated by multiple pathways for aerosol nitrate formation, each with uncertain rate parameters. Here, the Community Multiscale Air Quality model (CMAQ) simulated regional atmospheric nitrate budgets during the 2009 LADCO Winter Nitrate Study, using integrated process rate (IPR) and integrated reaction rate (IRR) tools to quantify relevant processes. Total nitrate production contributing to PM 2.5 episodes is a regional phenomenon, with peak production over the Ohio River Valley and southern Great Lakes. Total nitrate production in the lower troposphere is attributed to three pathways, with 57% from heterogeneous conversion of N 2 O 5 , 28% from the reaction of OH and NO 2 , and 15% from homogeneous conversion of N 2 O 5 . TNO 3 formation rates varied day-to-day and on synoptic timescales. Rate-limited production does not follow urban–rural gradients and NO x emissions due to counterbalancing of urban enhancement in daytime HNO 3 production with nocturnal reductions. Concentrations of HNO 3 and N 2 O 5 and nighttime TNO 3 formation rates have maxima aloft (100–500 m), leading to net total nitrate vertical flux during episodes, with substantial vertical gradients in nitrate partitioning. Uncertainties in all three pathways are relevant to wintertime aerosol modeling, and highlight the importance of interacting transport and chemistry processes during ammonium nitrate episodes, as well as the need for additional constraint on the system through field and laboratory experiments.

Description: Due to a lack of industrialization in western China, surface air there was, until recently, believed to be relatively unpolluted. However, recent measurements and modeling studies have found high levels of ozone (O 3 ) there. Based on the state-of-the-science global chemical transport model MOZART-4, we identify the origin, pathway, and mechanism of trans-Eurasian transport of air pollutants to Western China in 2000. MOZART-4 generally simulates well the observed surface O 3 over inland areas of China. Simulations find surface ozone concentrations over Western China on average to be about 10 ppbv higher than Eastern China. Using sensitivity studies, we find that anthropogenic emissions from all Eurasian regions except China contribute 10–15 ppbv surface O 3 over western China, superimposed upon a 35–40 ppbv natural background. Transport from European anthropogenic sources to Northwestern China results in 2–6 ppbv O 3 enhancements in spring and summer. Indian anthropogenic sources strongly influence O 3 over the Tibetan Plateau during the summer monsoon. Transport of O 3 originating from emissions in the Middle East occasionally reach Western China and increase surface ozone there by about 1–4 ppbv. These influences are of similar magnitude as trans-Pacific and trans-Atlantic transport of O 3 and its precursors, indicating the significance of trans-Eurasian ozone transport in hemispheric transport of air pollution. Our study further indicates that mitigation of anthropogenic emissions from Europe, the Indian Subcontinent and the Middle East could benefit public health and agricultural productivity in Western China.

Description: Spectral nudging – a scale-selective interior constraint technique – is commonly used in regional climate models to maintain consistency with large-scale forcing while permitting mesoscale features to develop in the downscaled simulations. Several studies have demonstrated that spectral nudging improves the representation of regional climate in reanalysis-forced simulations compared with not using nudging in the interior of the domain. However, in the Weather Research and Forecasting (WRF) model, spectral nudging tends to produce degraded precipitation simulations when compared to analysis nudging – an interior constraint technique that is scale indiscriminate but also operates on moisture fields which until now could not be altered directly by spectral nudging. Since analysis nudging is less desirable for regional climate modeling because it dampens fine-scale variability, changes are proposed to the spectral nudging methodology to capitalize on differences between the nudging techniques and aim to improve the representation of clouds, radiation, and precipitation without compromising other fields. These changes include adding spectral nudging toward moisture, limiting nudging to below the tropopause, and increasing the nudging timescale for potential temperature, all of which collectively improve the representation of mean and extreme precipitation, 2-m temperature, clouds, and radiation, as demonstrated using a model-simulated 20-year historical period. Such improvements to WRF may increase the fidelity of regional climate data used to assess the potential impacts of climate change on human health and the environment and aid in climate change mitigation and adaptation studies.

Description: Relationships between synoptic activity and sea ice variability in the Arctic are studied using self-organizing maps (SOMs) to categorize observed weather patterns over the 1979–2013 period. The European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-interim) provides the daily-averaged sea level pressures from which the SOMs are computed. Time series of frequencies and durations of synoptic weather patterns are correlated with two sea ice metrics, Fram Strait ice outflow and year-to-year changes in September pan-Arctic sea ice extent. When compared to climate indices commonly used to predict sea ice, the Arctic Oscillation (AO), North Atlantic Oscillation (NAO), and Arctic Dipole (AD), some SOM patterns correlate as or more strongly with sea ice metrics. For example, Beaufort High synoptic patterns are increasing in frequency in spring and their summer frequencies are associated with ice loss. Arctic high pressure patterns are linked to ice loss through pressure gradients conducive to ice export. The phase lags between the SOM occurrences and sea ice variability offer the potential for augmentation of other approaches to seasonal sea ice prediction.

Description: In this study, we present the hygroscopic behaviour of water soluble matter (WSM) extracted from biomass-burning derived PM 2.5 aerosols collected at a rural background site in Tanzania during June-August 2011. Hygroscopic growth factors, g (RH), of WSM were measured by hygroscopic tandem differential mobility analyzer (H-TDMA) with an initial dry particle diameter of 100 nm. We observed that the g (RH) of WSM at 90% relative humidity (RH), g (90%) WSM , ranged from 1.10 to 1.47 with an average of 1.25 ± 0.12. The H-TDMA retrieved hygroscopicity parameter of WSM, κ WSM , ranged from 0.04 to 0.24 with a mean of 0.11 ± 0.07. We found that the observed g (90%) WSM is positively correlated with PM 2.5 mass fractions of K + (R 2  = 0.61), Cl − (0.54), and organic carbon (0.58). Moreover, it well correlates with levoglucosan (0.67) and total diacids (0.76), implying that although the inorganic fraction may be the most important factor to control the hygroscopicity, biomass-burning organics play a significant role in the hygroscopicity of Tanzanian aerosols. The lower growth factors obtained over the sampling site are probably due to the formation of less water-soluble potassium oxalate (K 2 C 2 O 4 ) or less hygroscopic K 2 SO 4 particles during atmospheric aging. We observed a moderate correlation (R 2  = 0.33) between PM 2.5 mass fraction of WSOC and g (90%) WSM . The retrieved g (90%) WSOM values ranged from 1.0 to 1.25 with a mean of 1.16 ± 0.05. This study demonstrates that the hygroscopicity of Tanzanian aerosols is largely controlled by the emission of biomass burning products and the subsequent chemical aging during atmospheric transport.

Description: An advanced meteor radar viz., SVU meteor radar (SVU MR) operating at 35.25 MHz was installed at Sri Venkateswara University (SVU), Tirupati (13.63°N, 79.4°E), India, in August 2013 for continuous observations of horizontal winds in the Mesosphere and Lower Thermosphere (MLT). This manuscript describes the purpose of the meteor radar, system configuration, measurement techniques, its data products and operating parameters, as well as a comparison of measured mean winds in the MLT with contemporary radars over the Indian region. It is installed close to the Gadanki (13.5°N, 79.2°E) MST radar to fill the region between 85 and 100 km where this radar does not measure winds. The present radar provides additional information due to its high meteor detection rate, which results in accurate wind information from 70 to 110 km. As a first step, we made a comparison of SVU MR-derived horizontal winds in the MLT region with those measured by similar and different (MST and MF radars) techniques over the Indian region, as well as model (Horizontal Wind Model 2007 (HWM-07)) data sets. The comparison showed an exquisite agreement between the overlapping altitudes (82–98 km) of different radars. Zonal winds compared very well, as did the meridional winds. The observed discrepancies and limitations in the wind measurement are discussed in the light of different measuring techniques and the effects of small-scale processes like gravity waves. This new radar is expected to play an important role in our understanding of the vertical and lateral coupling of different regions of the atmosphere that will be possible when measurements from nearby locations are combined.

Description: The annual accumulation and the physical properties of snow close to the surface on the Antarctic Plateau are characterized by a large decameter-scale variability resulting from snow drift, that is not simulated by one-dimensional snow evolution models.Here, the detailed snowpack model Crocus was adapted to Antarctic conditions and then modified to account for this drift-induced variability using a stochastic snow redistribution scheme. For this, 50 simulations were run in parallel and were allowed to exchange snow mass according to rules driven by wind speed. These simple rules were developed and calibrated based on in situ pictures of the snow surface recorded for two years. The simulation performed with this new model shows three substantial improvements with respect to standard Crocus simulations. First, significant and rapid variations of snow height observed in hourly measurements are well reproduced, highlighting the crucial role of snow drift in snow accumulation. Second, the statistics of annual accumulation is also simulated successfully, including the years with net ablation which are as frequent as 15% in the observations and 11% in the simulation. Lastly, the simulated vertical profiles of snow density and specific surface area down to 50 cm depth were compared to 98 profiles measured at Dome C during the summer 2012-2013. The observed spatial variability is partly reproduced by the new model, especially close to the surface. The erosion/deposition processes explain why layers with density lower than 250 kg m −3 or specific surface area larger than 30 m 2  kg −1 can be found deeper than 10 cm.

Description: The new mission concept of microwave and infrared-laser occultation between Low Earth Orbit satellites (LMIO) is capable to provide accurate, consistent, and long-term stable measurements of many essential climate variables. These include temperature, humidity, key greenhouse gases (GHGs) such as carbon dioxide and methane, and line-of-sight wind speed, all with focus on profiling the upper troposphere and lower stratosphere. The GHG retrieval performance from LMIO data was so far analyzed under clear-air conditions only, without clouds and scintillations from turbulence. Here we present and evaluate an algorithm, built into an already published clear-air algorithm, which copes with cloud and scintillation influences on the infrared-laser transmission profiles used for GHG retrieval. We find that very thin ice clouds fractionally extinct the infrared-laser signals, thicker but broken ice clouds block them over limited altitude ranges, and liquid water clouds generally block them so that their cloud top altitudes typically constitute the limit to tropospheric penetration of profiles. The advanced algorithm penetrates through broken cloudiness. It achieves this by producing a cloud flagging profile from cloud-perturbed infrared-laser signals, which then enables bridging of transmission profile gaps via interpolation. Evaluating the retrieval performance with quasi-realistic end-to-end simulations, including high-resolution cloud data and scintillations from turbulence, we find a small increase only of GHG retrieval r.m.s. errors due to broken-cloud scenes and the profiles remain essentially unbiased as in clear air. These results are encouraging for future LMIO implementation, indicating that GHG profiles can be retrieved through broken cloudiness, maximizing upper troposphere coverage.

Description: The variation of ice crystal properties in the tops of deep convective clouds off the north coast of Australia is analyzed. Cloud optical thickness, ice effective radius, aspect ratio of ice crystal components, crystal distortion parameter and asymmetry parameter are simultaneously retrieved from combined measurements of the Moderate-resolution Imaging Spectroradiometer (MODIS) and Polarization and Directionality of the Earth's Reflectances (POLDER) satellite instruments. The data is divided into periods with alternating weak and strong convection. Mostly plate-like particle components with aspect ratios closer to unity and lower asymmetry parameters characterize strongly convective periods, while weakly convective periods generally show loweraspect ratios, relatively more column-like shapes and somewhat greater asymmetry parameters. Results for strongly convective periods show that, with increasing cloud top temperature, the distortion parameter generally decreases, while the asymmetry parameter and effective radius increase. For one of the strongly convective periods, the rate at which effective radii increase with cloud top temperature is more than double that of the other periods, while the temperature dependence of the other microphysical quantities for this period is substantially weaker. Atmospheric state analysis indicates that these differences are concurrent with differences in middle-to-upper tropospheric zonal wind shear. The observed variation of microphysical properties may have significant effects on the shortwave radiative fluxes and cloud absorption associated with deep convection. Additionally, MODIS collection 5 effective radii are estimated to be biased small with an artificially narrow range. Collection 6 products are expected to have less severe biases that depend on cloud top temperature and atmospheric conditions.

Description: We present laboratory measurements of biomass burning aerosol light scattering and absorption coefficients at 405, 532 and 781 nm and investigate their relationship with aerosol composition and fuel type. Aerosol composition measurements included non-refractory components measured by a high-resolution aerosol mass spectrometer (AMS), composition of refractory black carbon-containing particles by a soot particle aerosol mass spectrometer (SP-AMS) and refractory black carbon measured by a single particle soot photometer (SP2). All measurements were performed downstream of a thermal denuder system to probe the effects of non-refractory material on observed optical properties. The fires studied emitted aerosol with a wide range of optical properties with some producing more strongly light absorbing particles (single scattering albedo or SSA at 781 nm =0.4) with a weak wavelength dependence of absorption (absorption Ångström exponent or AAE =1-2) and others producing weakly light absorbing particles (SSA at 781 nm ~1) with strong wavelength dependence of absorption (AAE ~7). Removal of non-refractory material from the particles by the thermal denuder system led to substantial (20-80%) decreases in light absorption coefficients, particularly at shorter wavelengths, reflecting the removal of light absorbing material that had enhanced BC absorption in internally-mixed untreated samples. Observed enhancements of absorption by all mechanisms were at least factors of 1.2-1.5 at 532 nm and 781 nm as determined from the heated samples. A mass absorption cross-section based approach indicated larger enhancements, particularly at shorter wavelengths.

Description: This study attempts to understand interactions between midlatitude convective systems and their environments through a heat and moisture budget analysis using the sounding data collected from the Midlatitude Continental Convective Clouds Experiment (MC3E) in central Oklahoma. Distinct large-scale structures and diabatic heating and drying profiles are presented for cases of weaker and elevated thunderstorms as well as intense squall line and supercell thunderstorm events during the campaign. The elevated cell events were nocturnal convective systems occurring in an environment having low CAPE and a very dry boundary layer. In contrast, deeper convective events happened during the morning into early afternoon within an environment associated with large CAPE and a near-saturated boundary layer. As the systems reached maturity, the diagnosed diabatic heating in the latter deep convective cases was much stronger and of greater vertical extent than the former. Both groups showed considerable diabatic cooling in the lower troposphere, associated with the evaporation of precipitation and low-level clouds. The horizontal advection of moisture also played a dominant role in moistening the lower troposphere, particularly for the deeper convective events, wherein the near surface south-easterly flow allows persistent low-level moisture return from the Gulf of Mexico to support convection. The moisture convergence often was present before these systems develop, suggesting a strong correlation between the large-scale moisture convergence and convection. Sensitivity tests indicated that the uncertainty in the surface precipitation and the size of analysis domain mainly affected the magnitude of these analyzed fields rather than their vertical structures.

Description: Models describing the partitioning of atmospheric oxidized mercury (Hg(II)) between the gas and fine particulate phases were developed as a function of temperature. The models were derived from regression analysis of the gas-particle partitioning parameters, defined by a partition coefficient (K p ) and Hg(II) fraction in fine particles (f PBM ), and temperature data from 10 North American sites. The generalized model, Log(1/K p ) = 12.69–3485.30(1/T) (R 2  = 0.55; root mean squared error (RMSE) of 1.06 m 3 /µg for K p ), predicted the observed average K p at 7 of the 10 sites. Discrepancies between the predicted and observed average K p were found at the sites impacted by large Hg sources because the model had not accounted for the different mercury speciation profile and aerosol compositions of different sources. Site-specific equations were also generated from average K p and f PBM corresponding to temperature interval data. The site-specific models were more accurate than the generalized K p model at predicting the observations at 9 of the 10 sites as indicated by RMSE of 0.22-0.5 m 3 /µg for K p and 0.03-0.08 for f PBM . Both models reproduced the observed monthly average values, except for a peak in Hg(II) partitioning observed during summer at two locations. Weak correlations between the site-specific model K p or f PBM and observations suggest the role of aerosol composition, aerosol water content, and relative humidity factors on Hg(II) partitioning. The use of local temperature data to parameterize Hg(II) partitioning in the proposed models potentially improves the estimation of mercury cycling in chemical transport models and elsewhere.

Description: Dust particles from the Taklimakan Desert can be lofted vertically up to 10 km due to the unique topography and northeasterly winds associated with certain synoptic conditions. Then they can be transported horizontally to regions far downwind by westerlies. We combined data from the Multi-angle Imaging SpectroRadiometer (MISR) and the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) to investigate the three-dimensional distribution of dust over the Taklimakan Desert and surrounding areas. During spring and summer, a dust belt with high aerosol optical depths (AOD) extends eastward from the Taklimakan Desert to the Loess Plateau along the Hexi Corridor, and southward to the Tibetan Plateau. However, the dust extinction coefficients decrease rapidly from 0.340 km −1 near surface to 0.015 km −1 at 5 km in spring, while the extinction values vary within 0.100 ± 0.020 between the altitudes of 1.6 and 3.5 km and decrease to 0.023 km −1 at 5 km in summer indicating that dust aerosol is relatively well mixed vertically. We further used MISR daily AOD to identify high and low dust days, and then analyzed composite difference patterns of temperature, geopotential height and wind between high and low dust days. It was found that although the synoptic situations of spring and summer are quite different, there are two common features: a strong anticyclonic wind anomaly over the Taklimakan at 500 hPa and an enhanced easterly wind over the Tarim Basin at 850 hPa for the two seasons. These conditions are favorable for dust entrainment from the dry desert surface, vertically lofting and horizontal transport.

Description: This paper describes luminosity and leader propagation during the initial breakdown (IB) stage of a cloud-to-ground flash, beginning at 6.06 km altitude and 31.86 ms before the return stroke (RS). High-speed video (50,000 frames per s) and time-correlated electric field change (E-change) data show multiple branch ends advance concurrently in the first 6 ms of the flash; each branch begins with IB pulses and propagates first via bursts as an initial leader. Burst luminosity (pixel intensity) is directly related to IB pulse amplitude. Some initial leader branches transition to advancing as stepped leaders after a few milliseconds. Each initial leader branch end makes the transition to a stepped leader branch end at a different time, resulting in a complex E-change waveform including relatively narrow step-type pulses during the IB stage and no apparent Intermediate stage prior to the Leader stage. There is no visible evidence of an upward propagating leader end prior to the RS, nor of any light above the earliest visible IB luminosity prior to or during the RS. During the RS, the topmost visible portion of the channel that developed as an initial leader (above 5.1 km) behaves differently from the channel below, indicating it is less conductive. Radar and time-of-arrival lightning source data indicate that the IB luminosity visible to the camera comes from about 6 km inside the thundercloud echo. The 1276-m long initial leader transitions to a stepped leader at 4.9-5.0 km, near the altitude of the radar bright band.

Description: Aerosol-cloud interactions are affected by the rate at which water vapour condenses onto particles during cloud droplet growth. Changes in droplet growth rates can impact cloud droplet number and size distribution. The current study investigated droplet growth kinetics of acidic and neutral sulfate particles which contained various amounts and types of organic compounds, from model compounds (carbonyls) to complex mixtures (α-pinene SOA and diesel engine exhaust). In most cases, the formed droplet size distributions were shifted to smaller sizes relative to control experiments (pure sulfate particles), due to suppression in droplet growth rates in the cloud condensation nuclei counter. The shift to smaller droplets correlated with increasing amounts of organic material, with the largest effect observed for acidic seed particles at low relative humidity. For all organics incorporated onto acidic particles, formation of high molecular weight compounds was observed, probably by acid-catalyzed Aldol condensation reactions in the case of carbonyls. To test the reversibility of this process, carbonyl experiments were conducted with acidic particles exposed to higher relative humidity. High molecular weight compounds were not measured in this case and no shift in droplet sizes was observed, suggesting that high molecular weightcompounds are the species affecting the rate of water uptake. While these results provide laboratory evidence that organic compounds can slow droplet growth rates, the modeled mass accommodation coefficient of water on these particles (α 〉0.1) indicates that this effect is unlikely to significantly affect cloud properties, consistent with infrequent field observations of slower droplet growth rates.

Description: We have been developing an LF sensor network called Broadband Observation network for Lightning and Thunderstorm (BOLT), to image the structure of lightning discharges in 3D using time of arrival (TOA) technique. This paper documents initial results and characteristics of BOLT source locations for further understanding of LF radiation associated with lightning. Theoretical reduced Chi-square distribution fitted to BOLT observation data indicates a root mean square (rms) timing error of about 200 ns for each sensor. Monte Carlo simulations of BOLT indicate that at an altitude of 5000 m the standard deviations for horizontal differences between a known source and a location that the BOLT algorithm produces are less than 200 m, and vertical differences are less than 400 m in most of the network. Furthermore, comparison of BOLT and VHF source locations arriving at the same site within 5 µs indicates the average difference for elevation direction is 0.73° with a standard deviation of 3.64°, and that for the azimuth direction is 0.58° with a standard deviation of 1.98°. Lightning flash processes of intracloud (IC) and cloud-to-ground (CG) flashes, including preliminary breakdown pulses, negative leaders, breakdown in the negative charge region (NCR), and an attempted leader, are well imaged by BOLT. Normalized amplitudes in E-field change waveform of BOLT sources associated with negative leaders and breakdown occurred in the NCR do not have significant difference, implying that most BOLT sources in the NCR might be associated with negative recoil leaders.

Description: The link between high precipitation in Dronning Maud Land (DML), Antarctica, and the large-scale atmospheric circulation is investigated using ERA-Interim data for 1979-2009. High precipitation events are analyzed at Halvfarryggen situated in the coastal region of DML and at Kohnen Station located in its interior. This study further includes a comprehensive comparison of high precipitation in ERA-Interim with precipitation data from the Antarctic Mesoscale Prediction System (AMPS) and snow accumulation measurements from automatic weather stations (AWSs), with the limitations of such a comparison being discussed. The ERA-Interim and AMPS precipitation data agree very well. However, the correspondence between high precipitation in ERA-Interim and high snow accumulation at the AWSs is relatively weak. High precipitation events at both Halvfarryggen and Kohnen are typically associated with amplified upper-level waves. This large-scale atmospheric flow pattern is preceded by the downstream development of a Rossby wave train from the eastern South Pacific several days before the precipitation event. At the surface, a cyclone located over the Weddell Sea is the main synoptic ingredient for high precipitation both at Halvfarryggen and at Kohnen. A blocking anticyclone downstream is not a requirement for high precipitation per se, but a larger share of blocking occurrences during the highest precipitation days in DML suggests that these blocks strengthen the vertically integrated water vapor transport (IVT) into DML. A strong link between high precipitation and the IVT perpendicular to the local orography suggests that IVT could be used as a “proxy” for high precipitation, in particular over DML's interior.

Description: An idealized general circulation model with an analytically described Newtonian cooling term is employed to study the occurrence rate of sudden stratospheric warmings (SSWs) over a wide range of parameters. In particular, the sensitivity of the SSW occurrence rates to orographic forcing and both relaxation temperature and damping rate is evaluated. The stronger the orographic forcing and the weaker radiative forcing (in both temperature and damping rate), the higher the SSW frequency. The separate effects of the damping rates at low and high latitudes are somewhat more complex. Generally, lower damping rates result in higher SSW frequency. However, if the low and high latitude damping rates are not the same, SSW frequency tends to be most sensitive to a fractional change in the lower of the two damping rates. In addition, the effect of the damping rates on the stratospheric residual circulation is investigated. It is found that higher high-latitude damping rate results in deeper but narrower circulation, whereas higher low-latitude damping rates cause strengthening of the streamfunction in the tropical mid to upper stratosphere. Finally, the relation between easily measured and compared climatological fields and the SSW occurrence rate is determined. The average stratospheric polar zonal mean zonal wind shows a strong anti-correlation with the SSW frequency. In the troposphere, there is a high correlation between the meridional temperature gradient and SSW frequency, suggesting that the strength of synoptic activity in the troposphere may be an important influence on SSW occurrence.

Description: Cloud condensation and ice nuclei in the troposphere are required precursors to cloud and precipitation formation, both of which influence the radiative balance of Earth. The initial stage of hailstone formation (i.e., the embryo) and the subsequent layered growth allow hail to be used as a model for the study of nucleation processes in precipitation. By virtue of the preserved particle and isotopic record captured by hailstones, they represent the unique form of precipitation that allows direct characterization of the particles present during atmospheric ice nucleation. Despite the ecological and economic consequences of hail storms, the dynamics of hailstone nucleation, and thus their formation, are not well understood. Our experiments show that hailstone embryos from three Rocky Mountain storms contained biological ice nuclei capable of freezing water at warm, sub-zero (°C) temperatures, indicating that biological particles can act as nucleation sites for hailstone formation. These results are corroborated by analysis of δD and δ 18 O from melted hailstone embryos, which show that the hailstones formed at similarly warm temperatures in situ. Low densities of ice nucleation active abiotic particles were also present in hailstone embryos, but their low concentration indicates they were not likely to have catalyzed ice formation at the warm temperatures determined from water stable isotope analysis. Our study provides new data on ice nucleation occurring at the bottom of clouds, an atmospheric region whose processes are critical to global climate models but which has challenged instrument-based measurements.

Description: This study investigates the relationship between the equatorial atmospheric angular momentum oscillation in the non-rotating frame and the quasi-diurnal lunar tidal potential. Between 2 and 30 days, the corresponding equatorial component, called Celestial Atmospheric Angular Momentum (CEAM), is mostly constituted of prograde circular motions, especially of a harmonic at 13.66 days, a side-lobe at 13.63 days, and of a weekly broad band variation. A simple equilibrium tide model explains the 13.66-day pressure term as result of the O 1 lunar tide. The powerful episodic fluctuations between 5 and 8 days possibly reflect an atmospheric normal mode excited by the tidal waves Q 1 (6.86 days) and σ 1 (7.095 days). The lunar tidal influence on the spectral band from 2 to 30 days is confirmed by two specific features, not occurring for seasonal band dominated by the solar thermal effect. First, Northern and Southern hemispheres contribute equally and synchronously to the CEAM wind term. Second, the pressure and wind terms are proportional, which follows from angular momentum budget considerations where the topographic and friction torques on the solid Earth are much smaller than the one resulting from the equatorial bulge. Sucha configuration is expected for the case of tidally-induced circulation, where the surface pressure variation is tesseral and cannot contribute to the topographic torque, and tidal winds blow only at high altitudes. The likely effects of the lunar-driven atmospheric circulation on Earth's nutation are estimated and discussed in light of the present-day capabilities of space geodetic techniques.

Description: A multiwave stochastic parameterization of nonorographic gravity waves (GWs), representing GWs produced by convection and a background of GWs in the midlatudes, is tuned and tested against momentum fluxes derived from long-duration balloon flights.The tests are done offline using datasets corresponding to the Southern Ocean during the Concordiasi campaign in 2010. We also adopt the limiting constraint that the drag produced by the scheme resembles that produced by a highly tuned spectral GW parameterization, the so called Hines scheme. Our results show that the parameterization can reproduce the momentum-flux intermittency measured during the campaign, which is relevant since it strongly impacts on the vertical distribution of the GW drag. We also show that, at the altitude of the balloon flights, the momentum-flux intermittency is in good part due to the GW sources: filtering by the background winds only becomes effective at much higher altitude. These results are based on bulk formulae for the GW momentum flux that could be used to replace our background GWs by GWs produced by fronts. Finally, the GW energy spectra built out of the stochastic scheme by averaging over a large ensemble of realizations are comparable to the classical vertical spectra of GWs, used today in globally spectral schemes. This indicates that multiwave and spectral schemes can be reconciled once a stochastic approach is used.

Description: To remove the deficiency of the numerical solution of the mass conservation-based Richards equation for soil moisture in a regional climate model (RegCM4 with its land surface component CLM3.5), a revised numerical algorithm that is used in CLM4.5 is implemented into CLM3.5. Compared with in situ measurements, the modified numerical method improves the ground water table depth simulations in RegCM4. It also improves the temporal and spatial variability of soil moisture to some extent. Its impact on simulated summer precipitation is mixed, with improvements over three subregions in China but with increased errors in three other subregions. The impact on the simulated summer temperature is relatively small (with the mean biases changed by less than 10% over most subregions). The evapotranspiration differences between modified and control land-atmosphere coupled simulations are enhanced over the northwest subregion and Tibetan Plateau compared to offline simulations due to land surface feedbacks to the atmosphere (in coupled simulations). Similarly the soil moisture differences in coupled simulations are geographically different from those in offline simulations over the eastern monsoon area. The summer precipitation differences between modified and control coupled simulations are found to be explained by the differences of both surface evapotranspiration and large-scale water vapor flux convergence which have opposite signs over the northwest subregion and Tibetan Plateau but have the same signs over other subregions.

Description: We introduce an explicit emission tagging technique in the Community Atmosphere Model to quantify source-region-resolved characteristics of black carbon (BC), focusing on the Arctic. Explicit tagging of BC source regions without perturbing the emissions provides a physically consistent and computationally efficient approach to establish source-receptor relationships and transport pathways. Our analysis shows that the contributions of major source regions to the global BC burden are not proportional to the respective emissions due to strong region-dependent removal rates and lifetimes, while the contributions to BC direct radiative forcing show a near-linear dependence on their respective contributions to the burden. Arctic BC concentrations, deposition and source contributions all have strong seasonal variations. Eastern Asia contributes the most to the wintertime Arctic BC burden, but has much less impact on lower-level concentrations and deposition. Northern Europe emissions are more important to both surface concentration and deposition in winter than in summer. The largest contribution to Arctic BC in the summer is from Northern Asia. Although local emissions contribute less than 10% to the annual mean BC burden and deposition within the Arctic, the per-emission efficiency is much higher than for non-Arctic sources. The interannual variability (1996-2005) due to meteorology is small in annual mean BC burden and radiative forcing but is significant in yearly seasonal means over the Arctic. When a slow aging treatment of BC is introduced, the increase of BC lifetime and burden is source-dependent. Global BC forcing-per-burden efficiency also increases primarily due to changes in BC vertical distributions.

Description: The sources and composition of atmospheric marine aerosol particles (aMA) have been investigated with a range of physical and chemical measurements from open-ocean research cruises. This study uses the characteristic functional group composition (from Fourier transform infrared, or FTIR, spectroscopy) of aMA from five ocean regions to show that: (i) The organic functional group composition of aMA that can be identified as mainly atmospheric primary marine (ocean-derived) aerosol particles (aPMA) is 65 ± 12% hydroxyl, 21 ± 9% alkane, 6 ± 6% amine, and 7 ± 8% carboxylic acid functional groups. Contributions from photochemical reactions add carboxylic acid groups (15%-25%), shipping effluent in seawater and ship emissions add additional alkane groups (up to 70%), and coastal or continental emissions mix in alkane and carboxylic acid groups. (ii) The organic composition of aPMA is nearly identical to model generated primary marine aerosol particles from bubbled seawater (gPMA, which has 55 ± 14% hydroxyl, 32 ± 14% alkane, and 13 ± 3% amine functional groups), indicating that its overall functional group composition is the direct consequence of the organic constituents of the seawater source. (iii) While the seawater organic functional group composition was nearly invariant across all three ocean regions studied and the ratio of organic carbon to sodium (OC/Na + ) in the gPMA remained nearly constant over a broad range of chlorophyll- a concentrations, the gPMA alkane group fraction appeared to increase with chlorophyll- a concentrations (r =0.66). gPMA from productive seawater had a larger fraction of alkane functional groups (42 ± 9%) compared to gPMA from non-productive seawater (22 ± 10%), perhaps due to the presence of surfactants in productive seawater that stabilize the bubble film and lead to preferential drainage of the more soluble (lower alkane group fraction) organic components. gPMA has a hydroxyl group absorption peak location characteristic of monosaccharides and disaccharides, where the seawater OM hydroxyl group peak location is closer to that of polysaccharides. This may result from the larger saccharides preferentially remaining in the seawater during gPMA and aPMA production.

Description: Organized mesoscale cellular convection (MCC) is a common feature of marine stratocumulus clouds that forms in response to interactions among dynamic, microphysical, and radiative processes at the mesoscale. Cloud resolving models begin to resolve some of these processes but using high resolutions is extremely costly. To understand the impact of limited resolution on MCC, we use the Weather Research and Forecasting model with chemistry (WRF-Chem) and fully coupled cloud-aerosol interactions to simulate MCC over the southeast Pacific during the VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx). A suite of experiments with 3- and 9-km grid spacing indicates that the simulations with finer grid spacing have smaller liquid water paths and cloud fractions, while cloud tops are higher. The observed diurnal cycle is reasonably well simulated. To isolate organized MCC characteristics, we develop a new automated method that uses the watershed segmentation combining the detection of cloud boundaries with coincident vertical velocities. This ensures that the detected cloud fields are dynamically consistent for closed MCC, a common feature within the VOCALS-REx region. We demonstrate that the 3-km simulation is able to reproduce the scaling between horizontal cell size and boundary layer depth seen in satellite observations for the conditions of 900–1400 m deep boundary layers. However, the 9-km simulation is unable to resolve smaller circulations corresponding to shallower boundary layers, instead producing MCC with an invariant horizontal scale for all simulated boundary layers depths. The results demonstrate that the grid spacing needed for proper simulation of the MCC structure in marine stratocumulus regions depends on the boundary layer depth.

Description: The snowpack acts as a sink for atmospheric reactive nitrogen, but several post-depositional pathways have been reported to alter the concentration and isotopic composition of snow nitrate with implications for atmospheric boundary layer chemistry, ice core records and terrestrial ecology following snow-melt. Careful daily sampling of surface snow during winter (11 – 15 February, 2010) and spring-time (April 9 – May 5, 2010) near Ny-Ålesund, Svalbard reveals a complex pattern of processes within the snowpack. Dry deposition was found to dominate over post-depositional losses, with a net nitrate deposition rate of (0.6 ± 0.2) µmol m −2 d −1 to homogeneous surface snow. At Ny-Ålesund, such surface dry deposition can either solely result from long-range atmospheric transport of NO x,y or include the re-deposition of photolytic/bacterial emission originating from deeper snow layers. Our data further confirm that polar basin air masses bring 15  N-depleted nitrate to Svalbard, while high nitrate δ ( 18 O) values only occur in connection with ozone-depleted air, and show that these signatures are reflected in the deposited nitrate. Such ozone-depleted air is attributed to active halogen chemistry in the air-masses advected to the site. However, here the Ny-Ålesund surface snow was shown to have an active role in the halogen dynamics for this region, as indicated by declining bromide concentrations and increasing nitrate δ ( 18 O), during high BrO (low ozone) events. The data also indicates that the snow-pack BrO-NO x cycling continued in post-event periods, when ambient ozone and BrO levels recovered.

Description: Lightning flash initiation is studied using electric field change (E-change) measurements made in Florida. An Initial E-Change (IEC) was found immediately before the first initial breakdown (IB) pulse in both cloud-to-ground (CG) and intracloud (IC) flashes if the E-change sensor was within 80% of the reversal distance of the IEC. For 18 CG flashes the IECs had an average point dipole moment of 23 C m and an average duration of 0.18 ms; these parameters for 18 IC flashes were −170 C m and 1.53 ms. The IECs of CG flashes began with a change in slope of the E-change (with respect to time) from zero slope to a positive slope, consistent with downward motion of negative charge and/or upward motion of positive charge. For IECs of IC flashes the beginning slope change was from zero to negative slope, consistent with upward motion of negative charge and/or downward motion of positive charge. During an IEC the E-change monotonically increased for CG flashes and monotonically decreased for IC flashes. In 14 of 36 cases, the IEC beginning was coincident with a discrete, impulsive source of VHF radiation; another 13 cases had at least one VHF source during the IEC or the first IB pulse. Before the IECs, there were no preliminary variations detected in the 36 flashes. It is hypothesized that lightning initiation begins with an ionizing event that causes the IEC and that the IEC enhances the ambient electric field to produce the first IB pulse.

Description: A global assimilation that uses an Ensemble Kalman Filter and a set of derived scaling equations is presented for jointly adjusting the amount of atmospheric aerosol and the relative contribution of fine and coarse aerosol. The assimilation uses DOEand NSF's CAM model and aerosol optical depth (AOD) and Angstrom exponent (AE) retrievals from NASA's MODIS instrument. AERONET AE retrievals are used to constrain size over land. The presented system includes 60 ensemble members with a daily analysis, incorporating daily-averaged retrievals. A CAM control simulation and a CAM experiment with data assimilation (CAM-DA) are run for the year 2007. Control run comparisons to MODIS observations reveal a persistent negative bias in AOD, indicating an under-prediction of the amount of atmospheric aerosol (CAM: 0.09 (±0.06), MODIS:0.16 (±0.09) ). The negative bias decreased in the assimilation run with a globally averaged AOD of 0.12 (±0.05). CAM-DA is able to better capture spatial and temporal variations. A comparison of regional time series reveals the greatest reduction in model bias with respect to both aerosol amount and size over the oceans, especially the Southern Ocean. With respect to land regions, good agreement with AERONET AOD is found over the United States, Europe, and East Asia. Additionally, CAM-DA has clear spatial differences from the control with more aerosol and a larger fine contribution in the Northern hemisphere. The results also demonstrate the utility in assimilation methodologies for identifying systematic model biases, using the data assimilation correction fields as an indicator.

Description: Lightning Mapping Array (LMA) data are used to compare the propagation paths of seven rocket-triggered lightning flashes to the inferred charge structure of the thunderstorms in which they were triggered. This is the first LMA study of Florida thunderstorm charge structure. Three sequentially (within 16 minutes) triggered lightning flashes, whose initial stages were the subject of Hill et al . [2013], are re-examined by comparing the complete flashes to the preceding natural lightning to demonstrate that the three rocket-triggered flashes propagated through an inferred negative charge region that decreased from about 6.8 to about 4.4 km altitude as the thunderstorm dissipated. Two other flashes were also sequentially triggered (within 9 minutes) in a thunderstorm that contained a convectively intense region ahead of a stratiform region, with similar observed results. Finally, two unique cases of triggered lightning flashes are presented. In the first case, the in-cloud portion of the triggered lightning flash, after ascending to and turning horizontal at 5.3 km altitude, just above the 0 °C level, was observed to very clearly resemble the geometry of the in-cloud portion of the preceding natural lightning discharges. In the second case, a flash was triggered relatively early in the storm's lifecycle that did not turn horizontal near the 0 °C level, as is usually the case for triggered lightning in dissipating storms, but ascended to nearly 7.5 km altitude before exhibiting extensive horizontal branching.

Description: A long-lived mesoscale convective system (MCS) with extreme rainfall over the western coastal region of Guangdong on 10 May 2013 during the Southern China Monsoon Rainfall Experiment (SCMREX) is studied. The environmental conditions are characterized by little convective inhibition, low lifting condensation level, moderate convective available potential energy and precipitable water, and lack of low-level jets from the tropical ocean. Repeated convective backbuilding and subsequent northeastward " echo training" of convective cells are found during the MCS's development stages. However, the initiation/maintenance factors and organization of convection differ significantly during the earlier and later stages. From midnight to early-morning, convection is continuously initiated as southeasterly flows near the surface impinge on the east side of mesoscale mountains near the coastal lines and then moves northeastward, leading to formation of two quasi-stationary rainbands. From early-morning to early-afternoon, new convection is repeatedly triggered along a mesoscale boundary between precipitation-induced cold outflows and warm air from South China Sea and Gulf of Tokin, resulting in the formation of “band training” of several parallel rainbands that move eastward in a later time, i.e., two scales of “training” of convective elements are found. As the MCS dissipates, a stronger squall line moves into the region from the west and passes over within about 3.5 hours, contributing about 10%-15% to the total rainfall amount. It is concluded that terrain, near surface winds, warm advection from the upstream ocean in the boundary layer, and precipitation-generated cold outflows play important roles in initiating and maintaining the extreme-rain-producing MCS.

Description: Evolution of droplet size distribution (DSD) due to the water vapor diffusion in a vertically moving adiabatic parcels is investigated. Analytical expressions for height dependences of the main DSD parameters and DSD moments are obtained. The asymptotic behavior of the DSD parameters at large heights above cloud base is determined. It is shown that during diffusion growth, the width and the relative dispersion of the DSD decrease with height as z –1/3 and z –2/3 , respectively. The paper presents examples of DSD evolution in cases DSD forms on aerosols with a 3-mode lognormal distribution. The aerosol distribution parameters used in the study correspond to four aerosol types: " Marine" , " Clean continental" , " Background" and " extremely polluted Urban" . The vertical profiles of DSD parameters are compared with the asymptotic profiles. It is shown that in case of polydisperse DSD evolution, the vertical profile of supersaturation within several hundred meters above the cloud base can be approximated by a supersaturation profile corresponding to the " equivalent" monodisperse DSD. The initial radius of this " equivalent" DSD is equal to the mean radius of polydisperse DSD (haze size distribution) at cloud base, which is estimated using the Kohler theory. This result of the relation between the polydisperse and monodisperse solutions is universal. A new equation for estimation of supersaturation maximum for polydisperse case is obtained. The obtained analytical expressions and numerical results are useful for understanding the mechanisms of DSD formation in clouds and for parameterization of warm microphysical processes in cloud models.

Description: Global statistics of snowfall are currently only available from the CloudSat satellite. But CloudSat cannot provide observations of clouds and precipitation within the so-called blind-zone, which is caused by ground-clutter contamination of the CloudSatradar and covers the last [1200]m above land/ice surface. In this study, the impact of the blind-zone of CloudSat on derived snowfall statistics in polar regions is investigated by analyzing three 12-month datasets recorded by ground-based Micro Rain Radars (MRR) at the Belgian Princess Elisabeth station in East Antarctica and at Ny-Ålesund and Longyearbyen in Svalbard, Norway. MRR radar reflectivity profiles are investigated in respect to vertical variability in the frequencydistribution, changes in the number of observed snow events and impacts on total precipitation. Results show that the blind-zone leads to reflectivity being underestimated by up to [1]dB, the number of events being altered by ±5% and the precipitation amount being underestimated by 9 to 11 percentage points. Besides investigating a blind-zone of [1200]m, the impacts of a reduced blind-zone of [600]m are also analyzed. This analysis will help in assessing future missions with a smaller blind-zone. The reduced blind-zone leads to improved representation of mean reflectivity but does not improve the bias in event numbers and precipitation amount.

Description: In this study we investigate the diurnal precipitation cycle in high-resolution regional climate simulations for present (2000-2010) and future time periods (2030-2040 and 2040-2050) over sub-regions of the Himalayas. The future periods are simulated under a high emission scenario, Representative Concentration Pathway 8.5 (RCP8.5) in order to maximize any projected externally driven precipitation signal. For present climate, 4-hourly simulated precipitation is first evaluated against observations to establish model credibility. The diurnal cycle, which is typically characterized by a bimodal structure with primary (secondary) maxima in nighttime (afternoon), is reasonably well represented in the present, giving us confidence when assessing potential future changes. The timing of the precipitation maxima and minima is found to match the observed timings well in the diurnal cycle. In general, the WRF model captures the principal shape of the diurnal cycle observed over all the sub-regions. Under projected future conditions, no significant changes in the diurnal cycle occur. The results suggest modest changes in diurnal precipitation under RCP8.5 emission scenario, as evidenced by an increase in afternoon precipitation around of the Himalayas. Although the projected future changes of precipitation presented in this article are within of the expected range of precipitation changes caution must be exercised when interpreting single-model experiments.

Description: Two sets of field measured hyperspectral resolution Infrared (IR) emissivity spectra were taken from the CRCS Dunhuang site in China, with one representing daytime and the other representing nighttime. Comparisons of the two sets show that the daytime emissivity is smaller than the nighttime emissivity in almost the entire spectrum between 7.5 and 14 µm – strong field evidence to support emissivity diurnal variations, which have been reported in previous studies using satellite observations. These emissivities are used as a reference to evaluate three different emissivity products from the same site: the Atmospheric InfraRed Sounder (AIRS) operational emissivity products, the Moderate Resolution Imaging Spectroradiometer (MODIS) operational emissivity products, and the University of Wisconsin - Madison Hyperspectral Resolution IR emissivity (UWIREMIS) database. The AIRS emissivity does not agree as well with the field measurements when compared to that from MODIS and the UWIREMIS despite the fact that AIRS is hyperspectral; the likely cause for the disagreement is cloud contamination due to AIRS' large footprint. MODIS has the advantage of high spatial resolution and VIS/NIR channels to help the cloud mask, and is therefore less affected by cloud contamination. The V4.1 MODIS emissivity agrees better with the field measurement than the UWIREMIS, while the V5 does not do as well. The UWIREMIS emissivity, on the other hand, has the advantage of hyperspectral resolution, which makes it more useful for applications. The temporal analysis of the three satellite based emissivity products is also presented.

Description: Vertical profiles of light-absorbing particles in seasonal snow were sampled from 67 North American sites. Over 500 snow samples and 55 soil samples from these sites were optically analyzed for spectrally-resolved visible light absorption. The optical measurements were used to estimate black carbon (BC) mixing ratios in snow ( ),contributions to absorption by BC and non-BC particles, and the absorption Ångström exponent of particles in snow and local soil. Sites in Canada tended to have the lowest BC mixing ratios (typically ~5-35 ng g -1 ), with somewhat higher in the Pacific Northwest (typically ~5-40 ng g -1 ) and Intra-mountain Northwest (typically 10-50 ng g -1 ). The Northern U.S. Plains sites were the dirtiest, with typically ~15-70 ng g -1 and multiple sample layers with 〉100 ng g -1 BC in snow. Snow water samples were also chemically analyzed for standard anions, selected carbohydrates, and various elements. The chemical and optical data were input to a Positive Matrix Factorization analysis of the sources of particulate light absorption. These were soil, biomass/biofuel burning and fossil fuel pollution. Comparable analyses have been conducted for the Arctic and North China, providing a broad, internally consistent data set. As in North China, soil is a significant contributor to snow particulate light absorption in the Great Plains. We also examine the concentrations and sources of snow particulate light absorption across a latitudinal transect from the northern U.S. Great Plains to Arctic Canada by combining the current data with our earlier Arctic survey.

Description: Samples of ambient aerosols from the 2010 California Research at the Nexus of Air Quality and Climate Change (CalNex) field study were analyzed using negative ion mode Nanospray Desorption Electrospray Ionization High Resolution Mass Spectrometry (nano-DESI/MS). Four samples per day (6 hours each) were collected in Bakersfield, CA on June 20-24. Four characteristic groups were identified: molecules composed of carbon, hydrogen, and oxygen only (CHO), sulfur- (CHOS), nitrogen- (CHON), and both nitrogen- and sulfur-containing organics (CHONS). The chemical formula and elemental ratios were consistent with the presence of organonitrates, organosulfate, and nitroxy organosulfates in the negative ion mode mass spectra. The number of observed CHO compounds increased in the afternoon samples, suggesting photochemical processing as a source. The average number of CHOS compounds had the smallest changes during the day, consistent with a more broadly distributed source. Both of the nitrogen-containing groups (CHONS and CHON) had greater numbers of compounds in the early morning (midnight-6 am) and night (6 pm-midnight) samples, respectively, consistent with nitrate radical chemistry as a likely source for those compounds. Most of the compounds were found in submicron particles. The size distribution of the number of CHON compounds was bimodal, potentially indicating two types of sources. We conclude that the majority of the compounds observed were secondary in nature with both biogenic and anthropogenic sources. These data are complementary to previous results from positive ion mode nano-DESI/MS analysis of a sub-set of the same samples providing a more complete view of aerosol chemical composition at Bakersfield.

Description: In this study, we applied the integration methodology developed in the companion paper (Aires, 2014) by using real satellite observations over the Mississippi basin. The methodology provides basin scale estimates of the four water budget components (precipitation P , evapotranspiration E , water storage change ∆ S and runoff R ) in a two-step process: the Simple Weighting (SW) integration and a Post-processing Filtering (PF) that imposes the water budget closure. Acomparison with in situ observations of P and E demonstrated that PF improved the estimation of both components. A Closure Correction Model (CCM) has been derived from the integrated product (SW + PF), that allows to correct each observation dataset independently, unlike the SW + PF method which requires simultaneous estimates of the four components. The CCM allows to standardize the various datasets for each component and highly decrease the budget residual ( P  −  E  −  ΔS  −  R ). As a direct application, the CCM was combined with the water budget equation to reconstruct missing values in any component. Results of a Monte Carlo experiment with synthetic gaps demonstrated the good performances of the method, except for the runoff data that has a variability of the same order of magnitude as the budget residual. Similarly, we proposed a reconstruction of ∆ S between 1990 and 2002 where no GRACE-data is available. Unlike most of the studies dealing with the water budget closure at the basin scale, only satellite observations and in situ runoff measurements are used. Consequently the integrated datasets are model-independent and can be used for model calibration or validation.

Description: In California, emission control strategies have been implemented to reduce air pollutants. Here we estimate the changes in nitrogen oxides (NO x  = NO + NO 2 ) emissions in 2005-2010 using a state-of-the-art four-dimensional variational (4D-Var) approach. We separately and jointly assimilate surface NO 2 concentrations and tropospheric NO 2 columns observed by Ozone Monitoring Instrument (OMI) into the regional-scale STEM chemical transport model on a 12 × 12 km 2 horizontal resolution grid in May 2010. The assimilation generates grid-scale top-down emission estimates, and the updated chemistry fields are evaluated with independent aircraft measurements during the NOAA CalNex field experiment. The emission estimates constrained only by NO 2 columns, only by surface NO 2 , and by both indicate statewide reductions of 26%, 29%, 30% from ~0.3 Tg N/year in the base year of 2005, respectively. The spatial distributions of the emission changes differ in these cases, which can be attributed to many factors including the differences in the observation sampling strategies and their uncertainties, as well as those in the sensitivities of column and surface NO 2 with respect to NO x emissions. The updates in California's NO x emissions reduced the mean error in modeled surface ozone in the western US, even though the uncertainties in some urban areas increased due to their NO x -saturated chemical regime. The statewide reductions in NO x emissions indicated from our observationally-constrained emission estimates are also reflected in several independently-developed inventories: ~30% in the California Air Resources Board (CARB) bottom-up inventory, ~4% in the 2008 National Emission Inventory, and ~20% in the annual-mean top-down estimates by Lamsal et al. using the global GEOS-Chem model and OMI NO 2 columns. Despite the grid-scale differences among all top-down and bottom-up inventories, they all indicate stronger emission reductions in the urban regions. This study shows the potential of using space/ground-based monitoring data and advanced data assimilation approach to timely and independently update NO x emission estimates on a monthly scale and at a fine grid resolution. The well-evaluated results here suggest that these approaches can be applied more broadly.

Description: Understanding how precipitation varies as the climate changes is essential to determining the true impact of global warming. This is a difficult task not only due to the large internal variability observed in precipitation, but also because of a limited historical record and large biases in simulations of precipitation by General Circulation Models (GCMs). Here, we make use of a technique that spatially and seasonally transforms GCM fields to reduce location biases, and investigate the potential of this bias correction to study historical changes. We use two versions of this bias correction - one that conserves intensities, and another that conserves integrated precipitation over transformed areas. Focussing on multi-model ensemble means, we find that both versions reduce RMS error in the historical trend by approximately 11% relative to the Global Precipitation Climatology Project (GPCP) dataset. By regressing GCMs’ historical simulations of precipitation onto radiative forcings, wedecompose these simulations into anthropogenic and natural time-series. We then perform a simple detection and attribution study to investigate the impact of reducing location biases on detectability. A multiple ordinary least squares regression ofGPCP onto the anthropogenic and natural time-series, with the assumptions made, finds anthropogenic detectability only when spatial corrections are applied. The result is the same regardless of which form of conservation is used, and without reducing the dimensionality of the fields beyond taking zonal means. While ‘detectability’ is dependant both on the exact methodology, and the confidence required, this nevertheless demonstrates the potential benefits of correcting location biases in GCMs when studying historical precipitation, especially in cases where a signal was previously undetectable.

Description: We analyze trends in total column water vapor (TCWV) retrieved from independent satellite observations and retrieval schemes. GOME-SCIAMACHY (Global Ozone Monitoring Experiment-SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) measurements are carried out in the visible part of the solar spectrum and present a partly cloud-corrected climatology that is available over land and ocean. The HOAPS (Hamburg Ocean Atmosphere Parameters and Fluxes from Satellite Data) product, provided by EUMETSAT's Satellite Application Facility on Climate Monitoring (CM SAF) is based on passive microwave observations from the SSM/I (Special Sensor Microwave/Imager). It also includes the TCWV from cloudy pixels but is only available over oceans. The common observation time period is between 1996 and 2005. Due to the relatively short length of the period, the strong interannual variability with strong contributions from El Niño and La Niña events and the strong anomaly at the start of the common period, caused by the 1997/1998 El Niño, the observed trends should not be interpreted as long-term climate trends. After subtraction of average seasonality from monthly gridded data a linear model and a level shift model have been fitted to the HOAPS and GOME-SCIAMACHY data, respectively. Autocorrelation and cross-correlation of fit residuals are accounted for in assessing uncertainties in trends. The trends observed in both time series agree within uncertainty margins. This agreement holds true for spatial patterns, magnitudes and global averages. The consistency increases confidence in the reliability of the trends because the methods, spectral range and observation technique as well as the satellites and their orbits are completely independent of each other. The similarity of the trends in both data sets is an indication of sufficient stability in the observations for the time period of ≈10 years.

Description: ABSTRACT This study presents the results of high resolution (0.125°) climate simulations over a Chinese area performed with an optimized configuration of the regional climate model COSMO-CLM, driven by ERA-Interim Reanalysis over the period 1979-2011 and by the output of the global model CMCC-CM (resolution 0.75°) over the period 1979-2100. The main aim of this work was to analyze the capabilities of COSMO-CLM to describe the climate of China in the recent past; validation revealed a good improvement in reproducing the precipitation and a reasonable improvement in two-meter temperature representation compared to results reported elsewhere. Climate projections, under the new IPCC RCP4.5 and RCP8.5 emission scenarios, show a significant warming expected in China over the 21st century, while precipitation changes are expected only on a regional scale: increases in precipitation are projected for both scenarios in the northern part of the domain, while the southern area will be affected by a reduction in winter.

Description: The position and orientation of the South Pacific Convergence Zone (SPCZ), modulated by the El Niño-Southern Oscillation (ENSO) determines many of the potentially predictable interannual variations in rainfall in the South Pacific region. In this study, the predictability of the SPCZ in austral summer is assessed using two coupled ocean-atmosphere global circulation model (CGCM) based seasonal prediction systems: the Japan Meteorological Agency's JMA/MRI-CGCM; and the Australian Bureau of Meteorology's Predictive Ocean-Atmosphere Model for Australia (POAMA-M24). Forecasts of austral summer rainfall, initialised in November are assessed over the period 1980–2010. The climatology of CGCM precipitation in the SPCZ region compares favourably to rainfall analyses over subsets of years characterizing different phases of ENSO. While the CGCMs display biases in the mean SPCZ latitudes, they reproduce inter-annual variability in austral summer SPCZ position indices for forecasts out to four months, with temporal correlations greater than 0.6. The summer latitude of the western branch of the SPCZ is predictable with correlations of the order of 0.6 for forecasts initialised as early as September, while the correlation for the eastern branch only exceeds 0.6 for forecasts initialised in November. Encouragingly, the models are able to simulate the large displacement of the SPCZ during zonal SPCZ years 1982–83, 1991–92 and 1997–98.

Description: Regional convection-permitting model simulations of cloud populations observed during the 2011 Atmospheric Radiation Measurement (ARM) Madden-Julian Oscillation Investigation Experiment/ Dynamics of the Madden-Julian Oscillation Experiment (AMIE/DYNAMO) field campaign are evaluated against ground-based radar and ship-based observations. Sensitivity of model simulated reflectivity, surface rain rate, and cold pool statistics to variations of raindrop break-up/self-collection parameters in four state-of-the-art two-moment bulk microphysics schemes in the Weather Research and Forecasting (WRF) model are examined. The model simulations generally overestimate reflectivity from large and deep convective cells, underestimate stratiform rain and the frequency of cold pools. In the sensitivity experiments, introduction of more aggressive raindrop break-up or decreasing the self-collection efficiency increases the cold pool occurrence frequency in all of the simulations, and slightly reduces the reflectivity and precipitation statistics bias in some schemes but has little effect on the overall mean surface precipitation. Both the radar observations and model simulations of cloud populations show an approximate power-law relationship between convective echo-top height and equivalent convective cell radius.

Description: We examine changes in extreme rainfall indices over 57 major urban areas in India under the observed (1901–2010) and projected future climate (2010–2060). Between 1901 and 2010, only four out of the total 57 urban areas showed a significant (p-value 〈0.05) increasing trend in the monsoon maximum rainfall (MMR). Time varying trends for the various rainfall indices exhibited that only a few urban areas experienced significant increases in the extreme rainfall indices for the different periods. Moreover, rainfall maxima for 1–10 day durations and at 100 year return period did not change significantly over the majority of urban areas in the post 1955 period. Results do not indicate any significant change (p 〉 0.05) in the pooled mean and distribution of the extreme rainfall indices for the pre and post 1983 periods revealing an insignificant role of urbanization on rainfall extremes in the major urban areas in India. We find that at the majority of urban areas changes in the extreme rainfall indices are driven by large scale climate variability. Regional Climate Models (RCMs) that participated in the CORDEX-South Asia program showed a significant bias in the monsoon maximum rainfall and rainfall maxima at 100-year return period for the majority of urban areas. For instance, most of the models fail to simulate rainfall maxima within ±10% bias, which can be considered appropriate for a stormwater design at many urban areas. Rainfall maxima at 1–3 day durations and 100-year return period is projected to increase significantly under the projected future climate at the majority of urban areas in India. The number of urban areas with significant increases in rainfall maxima under the projected future climate is far larger than the number of areas that experienced significant changes in the historic climate (1901–2010), which warrants a careful attention for urban stormwater infrastructure planning and management.

Description: 35 sprite-producing lightning flashes were recorded in 9 nights in different seasons at the east coast of Spain with a 3D Lightning Mapping Array (LMA) since July 2011. A low-frequency time-of-arrival network provided data on emissions from return strokes and intracloud processes and a very-high-frequency interferometer network produced complementary lightning data. This study analyzes the bidirectional development of flashes in order to understand the positioning and timing of the positive cloud-to-ground stroke (+CG) and its consequences for charge neutralization by negative leaders, affecting sprite morphology. A summary of negative leader extents, altitudes and speeds before and after the + CG stroke is provided, as well as positive leader origins and inferred speeds. Negative leader speeds exhibited modes at 10 5 and 5 · 10 5  m s -1 . Five examples with different evolutions are discussed: (1) Slow bidirectional development with negative leader termination before the + CG stroke; (2) Fast bidirectional development with the negative leader continuing after the + CG stroke. (3) Slow-fast bidirectional development with a negative leader exhibiting a sudden lowering and speed increase; (4) Fast secondary bidirectional development from an in-cloud horizontal positive leader. Negative leaders propagated rapidly into the upper positive charge layer, continuing after the + CG stroke; (5) Slow bidirectional development with a long negative leader (50 km) subject to cut-off while the original positive leader remained trapped inside negative charge. A + CG stroke subsequently occurred under the old negative leader channel. Carrot sprites tended to be associated with fast extending leaders after the stroke, columniform/mixed sprites with slower side branches.

Description: Cloud detection is a critically important first step required to derive many satellite data products. A novel cloud detection algorithm designed for the cryosphere mission of GCOM-C1/SGLI is presented. This reflectance-based cloud detection scheme mainlyutilizes only two SWIR channels with dynamic thresholds that depend on sun-satellite viewing geometry to perform accurate cloud detection over snow/ice surfaces in high-latitude as well as high elevation regions. Profiles of atmospheric absorbing and scattering molecules as well as surface elevation are considered in the determination of the thresholds for the resulting Snow/ice Cloud Mask (SCM) algorithm. Image-based tests and statistical results have been used to validate the performance of the SCM over the Greenland plateau. Statistics using collocated CALIOP and MODIS Aqua observations over Greenland in 2007 show that over snow/ice surfaces the performance of the SCM is generally better than that of the MODIS Cloud Mask.

Description: We investigated the impact of roll convection on the convective boundary layer (CBL) and vertical transports in different cold-air outbreak (CAO) scenarios using large eddy simulations (LES). The organization of convection into rolls was triggered by upstream heterogeneities in the surface temperature, representing ice and water. By changing the sea-ice distribution in our LES, we were able to simulate a roll and a non-roll case for each scenario. Furthermore, the roll wavelength was varied by changing the scale of the heterogeneity. The characteristics of the simulated rolls and cloud streets, such as aspect ratios, orientation of the roll axes and downstream extensions of single rolls agreed closely with observations in CAO situations. The vertical turbulent fluxes, calculated for each simulation, were decomposed into contributions from rolls and from unorganized turbulence. Even though our results confirmed that rolls triggered by upstream heterogeneities can substantially contribute to vertical turbulent fluxes, the total fluxes were not affected by the rolls.

Description: No abstract is available for this article.

Description: The abilities of 27 Atmospheric Model Intercomparison Projection models to simulate the radiation budget (RB) over the East Asian Monsoon region (EAMR) are analyzed based on Clouds and the Earth's Radiant Energy System Energy Balanced and Filled, hereafter CERES, products. The regional mean values of annual top of the atmosphere (TOA) net RB in the simulations are constantly larger than the CERES values in the majority of the models (24 of 27), due mainly to the overestimation of its shortwave (SW) component. The TOA SW RB overestimation in most models (25 of 27) is due mainly to the insufficient SW absorption by the atmosphere and the consequent superfluous downwelling shortwave radiation reaching and being absorbed by the surface. Both the intensity underestimation of SW cloud radiative forcing (CRF) and the inadequate clear-sky atmospheric SW absorption contribute to the overestimation of TOA SW RB in the models. The underestimation of SW CRF intensity is mainly due to the reduced total cloud cover simulated in most of the models compared with the general circulation model -oriented CALIPSO Cloud Product. Black carbon explains the greatest part of the clear-sky atmospheric SW absorption biases in most of the models. The persistent underestimation of TOA SW CRF intensity over the EAMR across all seasons largely explains the seasonally constant overestimation of TOA SW RB. The seasonal variation in clear-sky LW RB demonstrates the remarkable seasonal variation in atmospheric and surface LW RB biases.

Description: The flux and chemical composition of aerosols impact the climate. Antarctic ice cores preserve the record of past atmospheric aerosols, providing useful information about past atmospheric environments. However, few studies have directly measured the chemical composition of aerosol particles preserved in ice cores. Here we present the chemical compositions of sulfate and chloride salts from aerosol particles in the Dome Fuji ice core. The analysis method involves ice sublimation, and the period covers the last termination, 25.0–11.0 thousand years before present (kyr BP), with a 350-year resolution. The major components of the soluble particles are CaSO 4 , Na 2 SO 4 , and NaCl. The dominant sulfate-salt changes at 16.8 kyr BP from CaSO 4 , a glacial-type, to Na 2 SO 4 , an interglacial-type. The sulfate-salt flux (CaSO 4 plus Na 2 SO 4 ) inversely correlates with δ 18 O in Dome Fuji over millennial timescales. This correlation is consistent with the idea that sulfate-salt aerosols contributed to the last deglacial warming of inland Antarctica by reducing the aerosol indirect effect. Between 16.3 and 11.0 kyr BP, the presence of NaCl suggests that winter atmospheric aerosols are preserved. A high NaCl/Na 2 SO 4 fraction between 12.3 and 11.0 kyr BP indicates that the contribution from the transport of winter atmospheric aerosols increased during this period.

Description: Climate change is expected to increase the frequency of hydrological extremes, producing more droughts and heavy rainfall events globally. How warm-season precipitation extremes will change over the Central U.S. is unclear because most coarse spatial resolution GCMs inadequately simulate hydrological extremes resulting from convective precipitation. However, the higher spatial resolution from dynamical downscaling potentially enables improved projections of future changes in extreme rainfall events. In this study, we downscaled two models from the Coupled Model Intercomparison Project – Phase 5 (CMIP5) using the Weather Research and Forecasting (WRF) model for one historical period (1990-1999), two future periods (2040-2049, 2090-2099) in a mid-range (RCP4.5) scenario, and one period (2090-2099) in a high emissions (RCP8.5) scenario. The diurnal cycle, extremes, and averages of precipitation in historical simulations compare well with observations. While the future change in the total amount of precipitation is unclear, model simulations suggest that summer rainfall will be less frequent, but more intense when precipitation does occur. Significant intensification of the heaviest rainfall events occurs in the models, with the greatest changes in the early warm-season (April). Increases in total April-July rainfall and the enhancement of extreme rainfall events in the RCP8.5 2090s is related to a stronger Great Plains Low Level Jet (GPLLJ) during those months. Conversely, late warm-season drying over the North Central U.S. is present in nearly all future simulations, with increased drought in August-September associated with a slight weakening of the GPLLJ. Simulated trends generally increase with stronger greenhouse gas forcing.