bluuebunny/crossref_metadata_2025 huggingface dataset:
Major 20th century changes of the content and chemical speciation of organic carbon archived in Alpine ice cores: Implications for the long‐term change of organic aerosol over Europe
Authors: Legrand M. , Preunkert S. , May B. , Guilhermet J. , Hoffman H. , Wagenbach D.
Published: April 2013

Dissolved organic carbon (DOC) and an extended array of organic compounds were investigated in an Alpine ice core covering the 1920–1988 time period. Based on this, a reconstruction was made of the long‐term trends of water‐soluble organic carbon (WSOC) aerosol in the European atmosphere. It is shown that light mono‐ and dicarboxylates, humic‐like substances, and formaldehyde account together for more than half of the DOC content of ice. This extended chemical speciation of DOC is used to estimate the DOC fraction present in ice that is related to WSOC aerosol and its change over the past. It is suggested that after World War II, the WSOC levels have been enhanced by a factor of 2 and 3 in winter and summer, respectively. In summer, the fossil fuel contribution to the enhancement is estimated to be rather small, suggesting that it arises mainly from an increase in biogenic sources of WSOC.
The role of the solar irradiance variability in the evolution of the middle atmosphere during 2004–2009
Authors: Shapiro A. V. , Rozanov E. V. , Shapiro A. I. , Egorova T. A. , Harder J. , Weber M. , Smith A. K. , Schmutz W. , Peter T.
Published: April 2013

Recent measurements by the Spectral Irradiance Monitor (SIM) and the Solar Stellar Irradiance Comparison Experiment (SOLSTICE) onboard the Solar Radiation and Climate Experiment satellite have revealed the spectral solar irradiance (SSI) changes in the ultraviolet between 2004 and 2009 to be several times higher than it was shown by all previous SSI measurements and reconstructions. In this paper, we simulate the O3, OH, and temperature responses to solar irradiance variability using four different SSI data sets trying to define which one gives the best agreement between the simulated and observed responses. First, we apply the 1‐D radiative‐convective model with interactive photochemistry to determine the regions of the atmosphere where the O3, OH, and temperature are most sensitive to the spectrum discrepancies between the different SSI data sets. As the comparison with observations can be only made taking into account dynamics and all known forcings of the atmosphere, we then apply the 3‐D chemistry‐climate model SOCOL to simulate the atmosphere evolution from May 2004 to February 2009. We compare the modeled OH, O3, and temperature changes with atmospheric data measured by several space instruments. Overall, the comparison shows that the atmospheric changes simulated with the 3‐D SOCOL model driven by the SIM and SOLSTICE SSI are closest to the atmospheric measurements.
Diurnal ozone variations in the stratosphere revealed in observations from the Superconducting Submillimeter‐Wave Limb‐Emission Sounder (SMILES) on board the International Space Station (ISS)
Authors: Sakazaki Takatoshi , Fujiwara Masatomo , Mitsuda Chihiro , Imai Koji , Manago Naohiro , Naito Yoko , Nakamura Tetsu , Akiyoshi Hideharu , Kinnison Douglas , Sano Takuki , Suzuki Makoto , Shiotani Masato
Published: April 2013

Considerable uncertainties remain in the global pattern of diurnal variation in stratospheric ozone, particularly lower to middle stratospheric ozone, which is the principal contributor to total column ozone. The Superconducting Submillimeter‐Wave Limb‐Emission Sounder (SMILES) attached to the Japanese Experiment Module (JEM) on board the International Space Station (ISS) was developed to gather high‐quality global measurements of stratospheric ozone at various local times, with the aid of superconducting mixers cooled to 4K by a compact mechanical cooler. Using the SMILES dataset, as well as data from nudged chemistry‐climate models (MIROC3.2‐CTM and SD‐WACCM), we show that the SMILES observational data have revealed the global pattern of diurnal ozone variations throughout the stratosphere. We also found that these variations can be explained by both photochemistry and dynamics. The peak‐to‐peak difference in the stratospheric ozone mixing ratio (total column ozone) reached 8% (1%) over the course of a day. This variation needs to be considered when merging ozone data from different satellite measurements and even from measurements made using one specific instrument at different local times.
Constrained dynamical downscaling for assessment of climate impacts
Authors: Harkey M. , Holloway T.
Published: April 2013

To assess climate change impacts on hydrology, conservation biology, and air quality, impact studies typically require future climate data with spatial resolution high enough to resolve urban‐rural gradients, complex topography, and sub‐synoptic atmospheric phenomena. We present here an approach to dynamical downscaling using analysis nudging, where the entire domain is constrained to coarser‐resolution parent data. Here meteorology from the North American Regional Reanalysis and the North American Regional Climate Change Assessment Program data archive are used as parent data and downscaled with the Advanced Research version of the Weather Research and Forecasting model to a 12 km × 12 km horizontal resolution over the Eastern U.S. Our results show when analysis nudging is applied to all variables at all levels, mean fractional errors relative to parent data are less than 2% for maximum 2 m temperatures, less than 15% for minimum 2 m temperatures, and less than 18% for10 m wind speeds. However, the skill of representing fields that are not nudged, such as boundary layer height and precipitation, is less clear. Our results indicate that though nudging can be a useful tool for consistent, comparable studies of downscaling climate for regional and local impacts, which variables are nudged and at what levels should be carefully considered based on the climate impact(s) of study.
Background conditions influence the decadal climate response to strong volcanic eruptions
Authors: Zanchettin Davide , Bothe Oliver , Graf Hans F. , Lorenz Stephan J. , Luterbacher Juerg , Timmreck Claudia , Jungclaus Johann H.
Published: April 2013

Background conditions have the potential to influence the climate response to strong tropical volcanic eruptions. As a case study, we systematically assess the decadal climate response to the April 1815 Tambora eruption in a set of full‐complexity Earth system model simulations. Three 10‐member simulation ensembles are evaluated which describe the climate evolution of the early 19th century under (1) full‐forcing conditions, (2) volcanic forcing–only conditions, and (3) volcanic forcing–only conditions excluding events preceding the Tambora eruption. The amplitude of the simulated radiative perturbation induced by the Tambora eruption depends only marginally on the background conditions. In contrast, simulated near‐surface atmospheric and especially oceanic dynamics evolve significantly differently after the eruption under different background conditions. In particular, large inter‐ensemble differences are found in the post‐Tambora decadal evolution of oceanic heat transport and sea ice in the North Atlantic/Arctic Ocean. They reveal the existence of multiple response pathways that depend on background conditions. Background conditions are therefore not merely a source of additive noise for post‐eruption decadal climate variability but actively influence the mechanisms involved in the post‐eruption decadal evolution. Hence, background conditions should appropriately be accounted for in future ensemble‐based numerical studies.
Climatology of aerosol optical properties at ACRF sites in the tropical warm pool region
Authors: Yin Bangsheng , Min Qilong
Published: April 2013

The long‐term multifilter rotating shadowband radiometer measurements at three Atmospheric Radiation Measurements Climate Research Facility sites of Darwin, Nauru, and Manus have been processed to develop the climatology of aerosols in the tropical warm pool region at the interannual, seasonal, and diurnal temporal scales. Due to their unique geolocations and associated large‐scale circulation patterns, aerosols at the Nauru site exhibit background oceanic characteristics (strongly correlated with the sea surface wind), aerosols at the Darwin site show strong influences by biomass‐burning aerosols, particularly in the dry season, and aerosols at the Manus site have climatologic characteristics in between the Darwin and Nauru sites. There are no obvious trends of aerosol loading for past decades at all three sites. El Niño/Southern Oscillation has its impacts on aerosol optical depth, as well as particle size and composition, at all three sites. Madden‐Julian Oscillation modulates aerosol optical depth at the Manus and Nauru sites along the equator but has no apparent impact at the Darwin site. The annual or seasonal variation of aerosols is closely linked with Indo‐Australian monsoons, exhibiting wet and dry season differences. The aerosol loading is significant lower with relatively larger particles in the wet season than in the dry season. There are significant diurnal cycles in both aerosol optical depth and Angstrom exponent at the Darwin site: low values of aerosol optical depth and Angstrom exponent in the midday and the two peaks in the early morning and late afternoon. There are noticeable changes between the dry and wet seasons. The amplitude of diurnal variation during La Niña periods is greater than that during El Niño periods. However, there are no significant diurnal variations of aerosol loading at the Manus and Nauru sites.
Thermodynamic structure and evolution of the atmospheric mixed layer over the western North Pacific during the summer monsoon onset
Authors: Geng Biao , Yoneyama Kunio , Shirooka Ryuichi
Published: April 2013

This study examined the thermodynamic structure of the atmospheric mixed layer and its evolution in different periods during the onset of the western North Pacific summer monsoon by using data observed on board the research vessel Mirai at 12°N and 135°E during 6–24 June 2008. The overall mean depth of the mixed layer was 482 m, and the mixed layer tended to shrink after the monsoon onset. The mixed layer was relatively warm and moist during the early onset period. However, the mixed layer became very cool and dry during the latter onset period, when intense and sustained rainfall was observed. The surface buoyancy flux, environmental subsidence over the mixed layer, and upward motion at cloud base intensified after the monsoon onset. All of these factors were negatively correlated with the depth of the mixed layer, which implies that the upward motion at cloud base and compensating environmental subsidence act to suppress the growth of the mixed layer driven by buoyancy forcing and to shrink the mixed layer after the monsoon onset. A significant positive correlation existed between the surface buoyancy flux and the upward motion at cloud base after the monsoon onset. Such positive feedback between the sea surface and cumulus clouds facilitates the formation of the warmer and moister mixed layer during the early onset period, thereby benefiting the further development of the monsoon onset.
Enhanced modern carbon and biogenic organic tracers in Northeast Asian aerosols during spring/summer
Authors: Pavuluri Chandra Mouli , Kawamura Kimitaka , Uchida Masao , Kondo Miyuki , Fu Pingqing
Published: April 2013

To better understand the organic aerosol (OA) sources and formation processes in Northeast Asia, we studied atmospheric aerosol (total suspended particulate matter (TSP)) samples collected from Sapporo, northern Japan over 1 year period for the measurement of radiocarbon (14C) in aerosol total carbon (TC) and water‐soluble organic carbon (WSOC). We also measured various organic tracers and carbonaceous components: organic carbon (OC), WSOC, and elemental carbon (EC). We found that the percent modern carbon (pMC) in TC and WSOC increased during spring/summer with maximum (85% and 117%, respectively) in May. The temporal variations of pMC in WSOC and TC showed a good agreement with changes in the contributions of biogenic OA tracers to OC and WSOC. We also found that emissions of pollen in spring and fungal spores from soil in summer/autumn as well as secondary OA formation from biogenic VOCs (BVOCs) in summer/autumn are responsible for the enhanced pMC. Although emissions from biomass burning are significant in winter, enhanced fossil fuel combustion lowers the pMC in WSOC and TC. Throughout the year, modern carbon is more enriched in WSOC fraction than in TC, indicating that WSOC is more associated with biological activity. This study warrants a need to reconcile the atmospheric models, considering seasonal differences in BVOC emissions, particularly in temperate regions, in estimating secondary OA budget and its climatic impacts.
Ground‐based validation of CALIPSO observations of dust and smoke in the Cape Verde region
Authors: Tesche M. , Wandinger U. , Ansmann A. , Althausen D. , Müller D. , Omar A. H.
Published: April 2013

Ground‐based Raman lidar measurements during the second Saharan Mineral Dust Experiment (SAMUM‐2) in 2008 were used for validation of measurements of the lidar aboard the Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite within the dusty environment of the Cape Verde region. SAMUM‐2 featured two one‐month campaigns in January/February and May/June 2008 to cover different modes of aerosol transport to the tropical Atlantic: dust from northern Africa and biomass‐burning smoke from western Africa during winter, and pure Saharan dust during summer. During the investigated time period, 33 CALIPSO overflights occurred at a distance of less than 500 km from the location of the ground‐based lidar. Fifteen out of these 33 cases were found suitable for comparing the findings of the two instruments. The parameters for this comparison are the particle backscatter coefficient at 532 and 1064 nm, the extinction coefficient, the lidar ratio (aerosol type), and the particle depolarization ratio at 532 nm, as well as the backscatter‐related Ångström exponent for the wavelength pair 532/1064 nm. Best agreement was found for the 532 nm backscatter coefficient, while the 532 nm extinction coefficient is underestimated by up to 30%. The latter is due to the use of an effective dust lidar ratio that gives reliable backscatter coefficients but is not suitable to transform these to extinction coefficients. CALIPSO particle depolarization ratios provided in the current (version 3.01) aerosol profile product were found to be affected by a computing error and should be calculated from the perpendicular and total particle backscatter coefficients provided in the same data file. CALIPSO aerosol classification was found to be mostly correct but a demand for homogeneous aerosol layers could improve the retrieval. Suggestions for the improvement of the CALIPSO retrieval by introducing iterative procedures are provided.
Evaluation of TRMM 3B42 precipitation estimates of tropical cyclone rainfall using PACRAIN data
Authors: Chen Yingjun , Ebert Elizabeth E. , Walsh Kevin J.E. , Davidson Noel E.
Published: April 2013

This study evaluates the latest release TRMM 3B42 version 7 (V7) estimates of daily rainfall in tropical cyclones (TCs) using the Comprehensive Pacific Rainfall Database (PACRAIN) of 24 h rain gauge observations. The evaluation is performed on two different terrain types: low‐lying atoll sites (assumed to represent open ocean conditions) and coastal and island sites (over land). The results show that TRMM 3B42 has good skill at detecting intense TC rainfall, with good correlation and pattern matching with PACRAIN observations. However, it tends to overestimate heavy rain frequency on atoll sites, but tends to underestimate heavy rain frequency on coastal and island sites. Overall, TRMM 3B42 is better able to estimate the intensity of TC heavy rain over ocean than over land. It is least skillful at coastal and island sites with high elevation, where it significantly underestimates TC heavy rainfall, suggesting that TRMM 3B42 is unable to capture orographic enhancement during TC landfall. Finally, results from V7 were compared with results from its predecessor, Version 6, showing that Version 7 of TRMM 3B42 has higher values on average for TC rain.
A hybrid dual‐source scheme and trapezoid framework–based evapotranspiration model (HTEM) using satellite images: Algorithm and model test
Authors: Yang Yuting , Shang Songhao
Published: April 2013

Satellite remote sensing techniques are widely considered as the most promising way to estimate evapotranspiration (ET) over large geographic extents. In this study, a hybrid dual‐source scheme and trapezoid framework–based evapotranspiration model (HTEM) is developed to map evapotranspiration from satellite imagery. It adopts a theoretically determined vegetation index/land surface temperature trapezoidal space to decompose bulk radiative surface temperature into component temperatures (soil and canopy) and uses a hybrid dual‐source scheme of the layer approach and patch approach to partition net radiation and estimate sensible and latent fluxes separately from the soil and canopy. The proposed model was tested at the Soil Moisture‐Atmosphere Coupling Experiment (SMACEX) site in central Iowa, USA, for 3 days during the campaign in 2002 using Landsat Thematic Mapper/Enhanced Thematic Mapper Plus (TM/ETM+) data, and at the Weishan flux site in the North China Plain during the main growing season of 2007 with Moderate Resolution Imaging Spectroradiometer Terra images. Results indicate that HTEM is capable of estimating latent heat flux (LE) with mean absolute percentage errors of 6.4% and 11.2% for the SMACEX and the Weishan sites, respectively. In addition, the model was found to be able to give reasonable evaporation and transpiration partitioning at both sites. Compared with other models, HTEM generally produced better sensible and latent flux estimates at the two sites and had comparable abilities in estimating net radiation and ground heat flux. Sensitivity analysis suggests that HTEM is most sensitive to temperature variables and less sensitive to other meteorological observations and parameters.
Impacts of ENSO on autumn rainfall over Yellow River loop valley in observation: Possible mechanism and stability
Authors: Li Chun , Zeng Gang
Published: April 2013

The Yellow River loop valley (YRLV) is one of major agricultural production zones in many Chinese dynasties. Predicting rainfall variability in the YRLV is important for the society and the economy. This study demonstrates impacts of El Niño–Southern Oscillation (ENSO) on autumn rainfall in the YRLV based on statistical analyses of instrumental rainfall in China and reanalyzed SST and atmospheric data. Results indicate that the autumn rainfall anomaly in the YRLV may be partially controlled by the ENSO‐like sea surface temperature (SST) pattern. The YRLV rainfall is below normal (above normal) in the El Niño (La Niña) developing years. This impact is mediated by an atmospheric response to the ENSO‐like SST anomaly forcing via a westward Rossby wave. Furthermore, Niño3.4 index may be used as a factor for autumn rainfall in the YRLV region with a lead of 4–5 months. However, the relationship between the autumn YRLV rainfall and ENSO does not persist and has gone through decadal weakening since the end of 1980s via a decadal response of atmospheric circulation to ENSO. The decadal change of the relationship between the autumn YRLV rainfall and ENSO may be modulated by climate decadal shifts.
An observational heat budget analysis of a coral reef, Heron Reef, Great Barrier Reef, Australia
Authors: MacKellar Mellissa C. , McGowan Hamish A. , Phinn Stuart R.
Published: April 2013

Measurements of the surface energy balance, the structure and evolution of the convective atmospheric reef layer (CARL), and local meteorology and hydrodynamics were made during June 2009 and February 2010 at Heron Reef, Australia, to establish the relative partitioning of heating within the water and atmosphere. Horizontal advection was shown to moderate temperature in the CARL and the water, having a cooling influence on the atmosphere, and providing an additional source or sink of energy to the water overlying the reef, depending on tide. The key driver of atmospheric heating was surface sensible heat flux, while heating of the reef water was primarily due to solar radiation, and thermal conduction and convection from the reef substrate. Heating and cooling processes were more defined during winter due to higher sensible and latent heat fluxes and strong diurnal evolution of the CARL. Sudden increases in water temperature were associated with inundation of warmer oceanic water during the flood tide, particularly in winter due to enhanced nocturnal cooling of water overlying the reef. Similarly, cooling of the water over the reef occurred during the ebb tide as heat was transported off the reef to the surrounding ocean. While these results are the first to shed light on the heat budget of a coral reef and overlying CARL, longer‐term, systematic measurements of reef thermal budgets are needed under a range of meteorological and hydrodynamic conditions, and across various reef types to elucidate the influence on larger‐scale oceanic and atmospheric processes. This is essential for understanding the role of coral reefs in tropical and sub‐tropical meteorology; the physical processes that take place during coral bleaching events, and coral and algal community dynamics on coral reefs.
Intraseasonal variations in the tropical tropopause temperature revealed by cluster analysis of convective activity
Authors: Nishimoto Eriko , Shiotani Masato
Published: April 2013

Space‐time variations of the tropical convective activities and temperatures around the tropical tropopause associated with the intraseasonal oscillation (ISO) are investigated using outgoing longwave radiation (OLR) data from the National Oceanic and Atmospheric Administration and atmospheric fields from the European Centre for Medium‐range Weather Forecasts Interim reanalysis data. By performing cluster analysis using the locus of convective activities observed in the unfiltered OLR field, the 72 ISO events selected during the southern summers from 1979–2011 are mainly grouped into four clusters. Two of the clusters exhibit the slow (<2 m/s) propagation speed in the unfiltered OLR field and the others fast (∼4 m/s). One cluster characterized as the El Niño phase has the fast speed while passing over the date line and another as the La Niña phase has the slow speed while propagating to ∼120°E. Compared with the other two clusters characterized as the weak El Niño‐Southern Oscillation phase, the speed is slow while propagating to ∼135°E when the SSTs over the Western Pacific are relatively low. Low temperatures around the tropical tropopause appear to the east of the eastward‐propagating convection in the tropics and to the west in the subtropics, forming a horseshoe‐shaped structure. The strength of the horseshoe‐shaped temperature structure is determined by that of the convective activities. Furthermore, the strength and location of the 100 hPa temperature minima differ among the clusters. This study implies that the different ISOs would cause different impacts on the dehydration process depending on their types.
Droplet activation properties of organic aerosols observed at an urban site during CalNex‐LA
Authors: Mei Fan , Hayes Patrick L. , Ortega Amber , Taylor Jonathan W. , Allan James D. , Gilman Jessica , Kuster William , de Gouw Joost , Jimenez Jose L. , Wang Jian
Published: April 2013

Size‐resolved cloud condensation nuclei (CCN) spectra and aerosol chemical composition were characterized at an urban supersite in Pasadena, California, from 15 May to 4 June 2010, during the CalNex campaign. The derived hygroscopicity (κCCN) of CCN‐active particles with diameter between 97 and 165 nm ranged from 0.05 to 0.4. Diurnal variation showed a slight decrease of κCCN from 8:00 to 16:00 (from 0.24 to 0.20), which is attributed to increasing organics volume fraction resulted from secondary organic aerosol (SOA) formation. The derived hygroscopicity distribution and maximum activated fraction of the size selected particles were examined as functions of photochemical age. The result indicates that condensation of secondary species (e.g., SOA and sulfate) quickly converted hydrophobic particles to hydrophilic ones, and during daytime, nearly every particle became a CCN at ~0.4% in just a few hours. Based on κCCN and aerosol chemical composition, the organic hygroscopicity (κorg) was derived, and ranged from 0.05 to 0.23 with an average value of 0.13, consistent with the results from earlier studies. The derived κorg generally increased with the organic oxidation level, and most of the variation in κorg could be explained by the variation of the organic O : C atomic ratio alone. The least squares fit of the data yielded κorg = (0.83 ± 0.06) × (O:C) + (−0.19 ± 0.02). Compared to previous results based on CCN measurements of laboratory generated aerosols, κorg derived from measurements during the CalNex campaign exhibited stronger increase with O : C atomic ratio and therefore substantially higher values for organics with average O : C greater than 0.5.
Influences of the Atlantic Ocean on the summer precipitation of the southeastern Tibetan Plateau
Authors: Ya Gao , Huijun Wang , Shuanglin Li
Published: April 2013

The southeastern Tibetan Plateau is one of the predominant summer rainfall regions in the world and is also the crucial water vapor channel of the Asian summer monsoon. The rainfall variability in the region influences not only the local communities but also downstream communities in East Asia. However, previous studies have exhibited large rainfall biases in this region in state‐of‐the‐art climate models. Understanding the observed rainfall variability provides an opportunity to identify the origin of model biases and to lay a foundation for improving model performance. In this study, the interannual variability of the summer precipitation (May–September) over the southeastern Tibetan Plateau was investigated based on National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis monthly mean data from 1979 to 2010. The associated atmospheric circulation anomalies of the southeastern Tibetan Plateau summer precipitation (SET_PR) display a North Atlantic Ocean‐Europe‐Asia teleconnection pattern, indicating a possible role of the Atlantic climate in the SET_PR. Further studies have revealed that the Atlantic sea surface temperature (SST) anomalies have the greatest influence on the SET_PR via the Rossby wave response, whereas the SST anomalies in the Indo‐Pacific have less of an influence on the SET_PR because their main impacts are confined to the western North Pacific subtropical high and the monsoonal circulation there. This paper also documents the detailed spatial pattern of the atmospheric circulation anomalies associated with the SET_PR and Atlantic SST year‐to‐year variability.
GCM simulations of anthropogenic aerosol‐induced changes in aerosol extinction, atmospheric heating and precipitation over India
Authors: Cherian Ribu , Venkataraman C. , Quaas J. , Ramachandran S.
Published: April 2013

The influence of anthropogenic emissions on aerosol distributions and the hydrological cycle are examined with a focus on monsoon precipitation over the Indian subcontinent, during January 2001 to December 2005, using the European Centre for Medium‐Range Weather Forecasts‐Hamburg (ECHAM5.5) general circulation model extended by the Hamburg Aerosol Module (HAM). The seasonal variability of aerosol optical depth (AOD) retrieved from the MODerate Resolution Imaging Spectroradiometer (MODIS) on board the Terra and Aqua satellite is broadly well simulated (R ≈ 0.6–0.85) by the model. The spatial distribution and seasonal cycle of the precipitation observed over the Indian region are reasonably well simulated (R ≈ 0.5 to 0.8) by the model, while in terms of absolute magnitude, the model underestimates precipitation, in particular in the south‐west (SW) monsoon season. The model simulates significant anthropogenic aerosol‐induced changes in clear‐sky net surface solar radiation (dimming greater than −7 W m−2), which agrees well with the observed trends over the Indian region. A statistically significant decreasing precipitation trend is simulated only for the SW monsoon season over the central‐north Indian region, which is consistent with the observed seasonal trend over the Indian region. In the model, this decrease results from a reduction in convective precipitation, where there is an increase in stratiform cloud droplet number concentration (CDNC) and solar dimming that resulted from increased stability and reduced evaporation. Similarities in spatial patterns suggest that surface cooling, mainly by the aerosol indirect effect, is responsible for this reduction in convective activity. When changes in large‐scale dynamics are allowed by slightly disturbing the initial state of the atmosphere, aerosol absorption in addition leads to a further stabilization of the lower troposphere, further reducing convective precipitation.
Evaluation of AMSR‐E retrievals and GLDAS simulations against observations of a soil moisture network on the central Tibetan Plateau
Authors: Chen Yingying , Yang Kun , Qin Jun , Zhao Long , Tang Wenjun , Han Menglei
Published: April 2013

A multi‐scale soil moisture and temperature monitoring network, consisting of 55 soil moisture and temperature measurement stations, has been established in central Tibetan Plateau (TP). In this study, the station‐averaged surface soil moisture data from the network are used to evaluate four soil moisture products retrieved from the Advanced Microwave Scanning Radiometer‐Earth Observing System (AMSR‐E) and four land surface modeling products from the Global Land Data Assimilation System (GLDAS). Major findings are (1) none of the four AMSR‐E products provides reliable estimates in the unfrozen season, in terms of the mission requirement of the root mean square error (RMSE) < 0.06 m3m−3. These algorithms either evidently overestimate soil moisture or obviously underestimate it, although some of them showed the soil moisture dynamic range, indicating that the retrieval algorithms have much space to be improved for the cold semi‐arid regions. (2) The four GLDAS models tend to systematically underestimate the surface soil moisture (0–5 cm) while well simulate the soil moisture for 20–40 cm layer. In comparison with the satellite surface soil moisture products, three among the four models give low RMSE and BIAS values, but still falling out of the acceptable range. The causes for the modeling biases in this cold region were discussed.
Observed trends in the global jet stream characteristics during the second half of the 20th century
Authors: Pena‐Ortiz Cristina , Gallego David , Ribera Pedro , Ordonez Paulina , Alvarez‐Castro Maria Del Carmen
Published: April 2013

In this paper, we propose a new method based on the detection of jet cores with the aim to describe the climatological features of the jet streams and to estimate their trends in latitude, altitude, and velocity in the National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) and 20th Century reanalysis data sets. Due to the fact that the detection method uses a single grid point to define the position of jet cores, our results reveal a greater latitudinal definition allowing a more accurate picture of the split flow configurations and double jet structures. To the best of our knowledge, these results provide the first multiseasonal and global trend analysis of jet streams based on a daily‐resolution 3‐D detection algorithm. Trends have been analyzed over 1958–2008 and during the post‐satellite period, 1979–2008. We found that, in general, trends in jet velocities and latitudes have been faster for the Southern Hemisphere jets and especially for the southern polar front jet which has experienced the fastest velocity increase and poleward shift over 1979–2008 during the austral summer and autumn. Results presented here show an acceleration and a poleward shift of the northern and southern winter subtropical jets over 1979–2008 that occur at a faster rate and over larger zonally extended regions during this latter period than during 1958–2008.
The effect of recombination and attachment on meteor radar diffusion coefficient profiles
Authors: Lee C. S. , Younger J. P. , Reid I. M. , Kim Y. H. , Kim J.‐H.
Published: April 2013

Estimates of the ambipolar diffusion coefficient producedusing meteor radar echo decay times display an increasing trend below 80–85 km, which is inconsistent with a diffusion‐only theory of the evolution of meteor trails. Data from the 33 MHz meteor radar at King Sejong Station, Antarctica, have been compared with observations from the Aura Earth Observing System Microwave Limb Sounder satellite instrument. It has been found that the height at which the diffusion coefficient gradient reverses follows the height of a constant neutral atmospheric density surface. Numerical simulations of meteor trail diffusion including dissociative recombination with atmospheric ions and three‐body attachment of free electrons to neutral molecules indicate that three‐body attachment is responsible for the distortion of meteor radar diffusion coefficient profiles at heights below 90 km, including the gradient reversal below 80–85 km. Further investigation has revealed that meteor trails with low initial electron line density produce decay times more consistent with a diffusion‐only model of meteor trail evolution.
SMILES ice cloud products
Authors: Millán L. , Read W. , Kasai Y. , Lambert A. , Livesey N. , Mendrok J. , Sagawa H. , Sano T. , Shiotani M. , Wu D. L.
Published: April 2013

Upper tropospheric water vapor and clouds play an important role in Earth's climate, but knowledge of them, in particular diurnal variation in deep convective clouds, is limited. An essential variable to understand them is cloud ice water content. The Japanese Superconducting Submillimeter‐Wave Limb‐Emission Sounder (SMILES) on board the International Space Station (ISS) samples the atmosphere at different local times allowing the study of diurnal variability of atmospheric parameters. We describe a new ice cloud data set consisting of partial Ice Water Path and Ice Water Content. Preliminary comparisons with EOS‐MLS, CloudSat‐CPR and CALIOP‐CALIPSO are presented. Then, the diurnal variation over land and over open ocean for partial ice water path is reported. Over land, a pronounced diurnal variation peaking strongly in the afternoon/early evening was found. Over the open ocean, little temporal dependence was encountered. This data set is publicly available for download in HDF5 format.
Eastern U.S. summer streamflow during extreme phases of the North Atlantic oscillation
Authors: Coleman Jill S. M. , Budikova Dagmar
Published: April 2013

Numerous studies have suggested streamflow discharge in the conterminous U.S. has been increasing, particularly in the east starting in the latter half of the 20th century. Northern Hemisphere (NH) hydroclimatic variability has been connected to shifts in large‐scale atmospheric teleconnection patterns. This study ascertained the spatial and temporal influences of the extreme phases of the North Atlantic Oscillation (NAO) on interannual streamflow variability across the eastern U.S. during the summer season. We also assessed the presence of any delayed streamflow responses to NAO configurations during previous spring (March‐April‐May) and winter (December‐January‐February) seasons across the study area. Methods of inquiry included the use of various statistical and compositing analyses applied to records of mean daily summer streamflow obtained from the Hydro‐Climatic Data Network between 1950 and 2010. Results of this study suggest that summer streamflow across eastern U.S. may be related to and thus potentially predicted from the NAO up to three seasons in advance, information of significant hydrologic consequences for the area. Depending upon the season and geographic location, the relationships may be both linear and nonlinear in nature and may be masked by the presence of temporal trends in the index. Summer streamflow across the eastern U.S., in general, displays greatest response to the negative phase of the NAO during the previous winter and the concurrent summer seasons. Geographically, the greatest potential for predictability exists across the Northeast where cohesive responses to NAO exist in all three seasons, winter, spring, and summer.
Evaluation of black carbon semi‒direct radiative effect in a climate model
Authors: Li Jiangnan , von Salzen Knut , Peng Yiran , Zhang Hua , Liang Xin‒Zhong
Published: April 2013

The semi‒direct effect of black carbon (BC) is studied by using a newly proposed optical property parameterization for cloud droplets with BC inclusions. Based on Atmospheric Model Intercomparison Project‒type climate model simulations, it is found that the cloud amount can be either enhanced or reduced when BC is included in clouds. The decrease of the global annual mean total cloud amount is only about 0.023%. The 3‒D cloud fraction distribution, however, shows larger changes which vary with latitude. A correlation between the changes of the cloud fraction and the vertical velocity is found. The cloud water path is mainly affected by low clouds and so the impact of BC on the cloud water path is particularly strong. It is shown that the BC above clouds tends to stabilize the atmosphere and enhance the cloud amount in the boundary layer. This can be used to explain the relationship between aerosol optical depth and cloud amount according to satellite data. For BC in clouds and above, the global annual mean enhancement of solar absorption is about 0.049 W m−2 and 0.57 W m−2, respectively. The BC semi‒direct radiative forcing is estimated by subtracting the BC direct forcing from the BC total radiative forcing. The global annual mean of BC direct forcing and semi‒direct forcing at the top of the atmosphere are 0.264 W m−2 and 0.213 W m−2, respectively.
Ozone variations over the northern subtropical region revealed by ozonesonde observations in Hanoi
Authors: Ogino S.‐Y. , Fujiwara M. , Shiotani M. , Hasebe F. , Matsumoto J. , T. Hoang Thuy Ha , T. Nguyen Tan Thanh
Published: April 2013

Seasonal and subseasonal variations in the ozone mixing ratio (OMR) are investigated by using continuous 7 year ozonesonde data from Hanoi (21°N, 106°E), Vietnam. The mean seasonal variations for the 7 years show large amplitude at the upper troposphere and lower stratosphere (UTLS) region (10–18 km) and at the lower troposphere (around 3 km) with standard deviations normalized by the annual mean value of about 30% for both regions. In the UTLS region, the seasonal variation in the OMR shows a minimum in winter and a maximum in spring to summer. The variation seems to be caused by the seasonal change in horizontal transport. Low OMR air masses are transported from the equatorial troposphere in winter by the anticyclonic flow associated with the equatorial convections, and high OMR air masses are transported from the midlatitude stratosphere in summer possibly due to Rossby wave breakings in the UT region and anticyclonic circulation associated with the Tibetan High in the LS region. In the lower troposphere, a spring maximum is found at 3 km height. Biomass burning and tropopause foldings are suggested as possible causes of this maximum. Subseasonal variations in the OMR show large amplitude in the UTLS region (at around 15 km) and in the boundary layer (below 1 km) with the standard deviations normalized by the annual mean larger than 40%. The OMR variations in the winter UTLS region have a negative correlation with the meridional wind. This relation indicates that the low OMRs observed at Hanoi has been transported from the equatorial region.
Estimate of aerosol absorbing components of black carbon, brown carbon, and dust from ground‐based remote sensing data of sun‐sky radiometers
Authors: Wang Ling , Li Zhengqiang , Tian Qingjiu , Ma Yan , Zhang Fengxia , Zhang Ying , Li Donghui , Li Kaitao , Li Li
Published: April 2013

Black carbon (BC), brown carbon (BrC), and mineral dust (DU) are three major light absorbing aerosols, playing important roles in climate change. Better knowledge of their concentrations is necessary for more accurate estimates of their radiative forcing effects of climate. We present a method to retrieve columnar contents of BC, BrC, and DU simultaneously from spectral refractive indices and spectral single scattering albedo obtained from the sun‐sky radiometer measurements. Then, this method is applied to investigate the columnar volume fractions and mass concentrations of BC, BrC, and DU in Beijing, China, based on measurements obtained from 2009 to 2010. Results show that among the three absorbing aerosols, DU dominates the largest volume fraction in the total aerosol volume (20–45%), followed by BrC (5–25%), and BC (< 5%). The retrieved monthly mean content of each absorbing component exhibits clear seasonal variation. BrC dominates in late fall and winter (40–92.5 mg/m2), whereas is extremely low in summer (< 10 mg/m2). DU dominates in spring, ranging from 270 to 405 mg/m2 (with volume fraction >30%), while during June–September, the DU fraction is generally lower than 30%. BC is characterized by low levels throughout the year. The monthly mean BC columnar mass concentration ([BC]) ranges from 2.7 to 7.3 mg/m2 with winter slightly higher than other seasons. As a preliminary validation, we compare our retrieved [BC] with in situ measurements. Similar day‐to‐day variation trends and good correlations are found between the retrieved [BC] and in situ measurements.
Trends in surface air temperature and temperature extremes in the Great Basin during the 20th century from ground‐based observations
Authors: Tang Guoping , Arnone John A.
Published: April 2013

We analyzed trends in surface air temperature and temperature extremes in the Great Basin during 1901–2010. We found that annual average daily minimum temperature increased significantly (0.9 ± 0.2°C) during the study period, with daily maximum temperature increasing only slightly. The asymmetric increase in daily minimum and maximum temperature resulted in daily diurnal temperature range (DTR) decreasing significantly from 1901 to 2010. Seasonally, increases in daily minimum temperature and decreases in DTR occurred in winter, summer, and autumn, but the rate of increase was faster in winter. In contrast, daily maximum temperature showed no significant trend in any season. These trends in temperature measures, however, were not monotonic with decadal periods that included either reversal or acceleration of century‐scale trends. The trend magnitudes in temperatures were not significantly associated with elevations. Increases in daily minimum temperature resulted in a decrease in the number of frost days (−0.14 ± 0.04 day yr−1) and cool nights (−0.09 ± 0.04 night yr−1) from 1901 to 2010, while the number of warm days (0.11 ± 0.04 day yr−1) and warm nights (0.19 ± 0.03 night yr−1) increased significantly. Surprisingly, the number of cool days and the length of the growing season showed no significant trend during the study period. Thus, the results of this study suggest that continuation of the overall warming trend would lead to markedly warmer conditions in upcoming decades.
On the potential high acid deposition in northeastern China
Authors: Cao Junji , Tie Xuexi , Dabberdt Walter F. , Jie Tang , Zhao Zhuzi , An Zhisheng , Shen Zhenxing , Feng Yinchang
Published: April 2013

There is an acid deposition conundrum in China: contrary to conventional wisdom, extremely high ambient sulfate concentrations in northeastern China are not always accompanied by correspondingly high acidities. To investigate this discrepancy, data from two independent sets of in situ field measurements were analyzed along with Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) satellite observations and Model for Ozone and Related chemical Tracers (MOZART) chemical transport model calculations. The field measurements included soluble aerosol ion concentrations and pH and particulate data from 11 cities, as well as pH measurement data from 74 sites in China. This study explores the basis for and the impacts of the large discrepancy in northeastern China between the major acidity precursors (SO2 and NOx) and measured acidity levels as indicated by pH values. There are extremely high SO2 emissions and ambient concentrations in northeastern China, while the corresponding acidity is unusually low (high pH) in this region. This is inconsistent with the usual situation where high‐acidity precursor pollutants result in low pH (high acidity) values and acid rain conditions. In other regions, such as southern China and the United States, high SO2 concentrations are typically well correlated with high acidities. Using measured soluble particle measurements (including both positively and negatively charged ions), it is seen that there are high values of alkaline ions in northeastern China that play an important role in neutralizing acidity in this region. This result strongly suggests that the high alkaline concentrations, especially Ca2+, increase warm season pH values by about 0.5 in northern China, partially explaining the inconsistency between sulfate concentrations and acidity. This has a very important implication for acid rain mitigation—especially in northeastern China. However, there are additional issues pertaining to the precursor‐acidity relationship that need further investigation. Why is it that the reduction in acidity due to the alkaline ions is only significant in summer? During winter, the measured alkaline ions play a much smaller role in explaining the discrepancy. The measured alkaline ions in this study were mostly obtained from particles in the PM2.5 range. However, the size of calcium particles is typically much larger—extending well beyond 2.5 µm—and so a significant amount of calcium may be underestimated by PM2.5 measurements alone. The under‐sampling of calcium particles is further exacerbated in that the sampling protocol excluded particle (and soluble ion and pH) measurements during dust storms. This all leads to the need for an improved understanding of pollutant‐ion‐particulate interactions in China, and their role in explaining the counter‐intuitive conclusion that dust mitigation strategies in China could have the unintended consequence of exacerbating acid rain conditions.
Lightning distribution with respect to the monsoon trough position during the Indian summer monsoon season
Authors: Penki Ramesh Kumar , Kamra A. K.
Published: April 2013

The location and shift in the position of the maximum lightning activity with respect to the position the of monsoon trough has been investigated in the region of 20°N–32°N and 75°E–95°E during the Indian summer monsoon seasons of 2002 and 2003 from the lightning imaging sensor (LIS) data from the Tropical Rainfall Measuring Mission (TRMM) satellite. The polynomial curve fitting the maximum lightning activity followed the position of the monsoon trough in both the normal monsoon and drought years. Observations of the maximal lightning activity in the TRMM‐LIS data collected during a period of 13 years, from 1998 to 2010, confirm these findings in the monsoon season. When the seasonal position of the monsoon trough moved from the plains to the submontane region of the Himalayas during a monsoon break period, the polynomial fitting of the maximum lightning activity also moved from the central Indian plains to that region. An empirical orthogonal function (EOF) analysis is applied to two different data sets of precipitation and observed high lightning flash rates over the monsoon trough region for the period of 1995–2005. The first and second components, EOF1 and EOF2, of precipitation values are out of phase with those of the flash rates. Our results imply that deep electrified convective systems during monsoon periods are responsible for the lightning activity in the monsoon trough region and that the lightning activity in this region can be used as a proxy for the location and shift of the seasonal monsoon trough.