bluuebunny/crossref_metadata_2025 huggingface dataset:
Boundary layer sources for the Asian anticyclone: Regional contributions to a vertical conduit
Authors: Bergman John W. , Fierli Federico , Jensen Eric J. , Honomichl Shawn , Pan Laura L.
Published: April 2013

The transport of air from the planetary boundary layer (PBL) into the Asian Summer Monsoon anticyclone is investigated using backward trajectories initiated within the anti‐cyclone at 100 mb and 200 mb during August 2011. Transport occurs through a well‐defined conduit centered over the southern Tibetan plateau, where convection lofts air parcels into the anticyclone. The conduit, as a dynamical feature, is distinct from the anticyclone. Thus, while the anticyclone influences transport through the upper troposphere and lower stratosphere, it does not by itself define a transport pipeline through that region. To quantify model sensitivities, parcel trajectories are calculated using wind fields from multiple analysis data sets (European Centre for Medium‐Range Weather Forecasts, National Center for Environmental Prediction's Global Forecasting System, and NASA's Modern‐Era Retrospective Analysis for Research and Applications [MERRA]) and from synthetically modified data sets that explore the roles of vertical motion and horizontal resolution for discrepancies among these calculations. All calculations agree on the relative contributions to PBL sources for the anticyclone from large‐scale regions with Tibetan Plateau and India/SE Asia being the most important. However, they disagree on the total fraction of air within the anticyclone that was recently in the PBL. At 200 mbar, calculations using MERRA are clear outliers due to problematic vertical motion in those data. Large differences among the different data sets at 100 mbar are more closely related to horizontal resolution. It is speculated that this reflects the importance of deep, small‐scale convective updrafts for transport to 100 mbar.
Effects of atmospheric light scattering on spectroscopic observations of greenhouse gases from space. Part 2: Algorithm intercomparison in the GOSAT data processing for CO2 retrievals over TCCON sites
Authors: Oshchepkov Sergey , Bril Andrey , Yokota Tatsuya , Wennberg Paul O. , Deutscher Nicholas M. , Wunch Debra , Toon Geoffrey C. , Yoshida Yukio , O'Dell Christopher W. , Crisp David , Miller Charles E. , Frankenberg Christian , Butz André , Aben Ilse , Guerlet Sandrine , Hasekamp Otto , Boesch Hartmut , Cogan Austin , Parker Robert , Griffith David , Macatangay Ronald , Notholt Justus , Sussmann Ralf , Rettinger Markus , Sherlock Vanessa , Robinson John , Kyrö Esko , Heikkinen Pauli , Feist Dietrich G. , Morino Isamu , Kadygrov Nikolay , Belikov Dmitry , Maksyutov Shamil , Matsunaga Tsuneo , Uchino Osamu , Watanabe Hiroshi
Published: April 2013

This report is the second in a series of companion papers describing the effects of atmospheric light scattering in observations of atmospheric carbon dioxide (CO2) by the Greenhouse gases Observing SATellite (GOSAT), in orbit since 23 January 2009. Here we summarize the retrievals from six previously published algorithms; retrieving column‐averaged dry air mole fractions of CO2 (XCO2) during 22 months of operation of GOSAT from June 2009. First, we compare data products from each algorithm with ground‐based remote sensing observations by Total Carbon Column Observing Network (TCCON). Our GOSAT‐TCCON coincidence criteria select satellite observations within a 5° radius of 11 TCCON sites. We have compared the GOSAT‐TCCON XCO2 regression slope, standard deviation, correlation and determination coefficients, and global and station‐to‐station biases. The best agreements with TCCON measurements were detected for NIES 02.xx and RemoTeC. Next, the impact of atmospheric light scattering on XCO2 retrievals was estimated for each data product using scan by scan retrievals of light path modification with the photon path length probability density function (PPDF) method. After a cloud pre‐filtering test, approximately 25% of GOSAT soundings processed by NIES 02.xx, ACOS B2.9, and UoL‐FP: 3G and 35% processed by RemoTeC were found to be contaminated by atmospheric light scattering. This study suggests that NIES 02.xx and ACOS B2.9 algorithms tend to overestimate aerosol amounts over bright surfaces, resulting in an underestimation of XCO2 for GOSAT observations. Cross‐comparison between algorithms shows that ACOS B2.9 agrees best with NIES 02.xx and UoL‐FP: 3G while RemoTeC XCO2 retrievals are in a best agreement with NIES PPDF‐D.
Field Measured Spectral Albedo–Four Years of Data from the Western U.S. Prairie
Authors: Michalsky Joseph J. , Hodges Gary B.
Published: April 2013

This paper presents an initial look at four years of spectral measurements used to calculate albedo for the Colorado prairie just east of the Rocky Mountain range foothills. Some issues associated with calculating broadband albedo from thermopile sensors are discussed demonstrating that uncorrected instrument issues have led to incorrect conclusions. Normalized Difference Vegetative Index (NDVI) is defined for the spectral instruments in this study and used to demonstrate the dramatic changes that can be monitored with this very sensitive product. Examples of albedo wavelength and solar‐zenith angle dependence for different stages of vegetative growth and senescence are presented. The spectral albedo of fresh snow and its spectral and solar‐zenith angle dependence are discussed and contrasted with other studies of these dependencies. We conclude that fresh snow is consistent with a Lambertian reflector over the solar incidence angles measured; this is contrary to most snow albedo results. Even a slope of a degree or two in the viewed surface can explain the asymmetry in the morning and afternoon albedos for snow and vegetation. Plans for extending these spectral measurements for albedo to longer wavelengths and to additional sites are described.
Updated analyses of temperature and precipitation extreme indices since the beginning of the twentieth century: The HadEX2 dataset
Authors: Donat M. G. , Alexander L. V. , Yang H. , Durre I. , Vose R. , Dunn R. J. H. , Willett K. M. , Aguilar E. , Brunet M. , Caesar J. , Hewitson B. , Jack C. , Klein Tank A. M. G. , Kruger A. C. , Marengo J. , Peterson T. C. , Renom M. , Oria Rojas C. , Rusticucci M. , Salinger J. , Elrayah A. S. , Sekele S. S. , Srivastava A. K. , Trewin B. , Villarroel C. , Vincent L. A. , Zhai P. , Zhang X. , Kitching S.
Published: April 2013

In this study, we present the collation and analysis of the gridded land‐based dataset of indices of temperature and precipitation extremes: HadEX2. Indices were calculated based on station data using a consistent approach recommended by the World Meteorological Organization (WMO) Expert Team on Climate Change Detection and Indices, resulting in the production of 17 temperature and 12 precipitation indices derived from daily maximum and minimum temperature and precipitation observations. High‐quality in situ observations from over 7000 temperature and 11,000 precipitation meteorological stations across the globe were obtained to calculate the indices over the period of record available for each station. Monthly and annual indices were then interpolated onto a 3.75° × 2.5° longitude‐latitude grid over the period 1901–2010. Linear trends in the gridded fields were computed and tested for statistical significance. Overall there was very good agreement with the previous HadEX dataset during the overlapping data period. Results showed widespread significant changes in temperature extremes consistent with warming, especially for those indices derived from daily minimum temperature over the whole 110 years of record but with stronger trends in more recent decades. Seasonal results showed significant warming in all seasons but more so in the colder months. Precipitation indices also showed widespread and significant trends, but the changes were much more spatially heterogeneous compared with temperature changes. However, results indicated more areas with significant increasing trends in extreme precipitation amounts, intensity, and frequency than areas with decreasing trends.
Identification of marine and continental aerosol sources in Paris using high resolution aerosol mass spectrometry
Authors: Crippa Monica , El Haddad Imad , Slowik Jay G. , DeCarlo Peter F. , Mohr Claudia , Heringa Maarten F. , Chirico Roberto , Marchand Nicolas , Sciare Jean , Baltensperger Urs , Prévôt André S. H.
Published: April 2013

Major summertime aerosol emission sources in Paris were assessed using a high resolution time‐of‐flight aerosol mass spectrometer (HR‐ToF‐AMS). The application of positive matrix factorization (PMF) to the highly mass and time‐resolved AMS measurements allowed the identification of primary and secondary sources of organic (OA) and sulfate aerosols. Primary anthropogenic emissions contributed on average ~27% (14.7% cooking, 12% traffic) to the total organic mass, while the major contribution to the organic fraction was associated with secondary formation products. Low‐volatility oxygenated OA (LV‐OOA, 25.2%) and semi‐volatile oxygenated OA (SV‐OOA, 32.4%) factors were classified as SOA. An additional component with high S : C and O : C ratios was identified and attributed to marine emissions (marine organic aerosol, MOA), owing to its high correlation with methanesulfonic acid (R2 = 0.84) and contributing on average 15.7% to the total OA mass, even in the continental megacity of Paris. Non‐sea salt sulfate was apportioned by including both organic and sulfate ions in the PMF data matrix. This allowed apportionment of submicron sulfate to continental versus marine sources. A detailed source apportionment of PM1 combining AMS, aethalometer, and filter data is presented.
Theoretical prediction of electric fields in wind‐blown sand
Authors: Bo TianLi , Zhang Huan , Zhu Wei , Zheng XiaoJing
Published: April 2013

Existing experimental and theoretical studies have identified the existence of an electric field in wind‐blown sand, whose strength is hundreds to thousands of times larger than that of the fair‐weather electric field (around 120v m− 1) and is related to the intensity of the wind‐blown sand transport. The direction of electric field is often upward pointing and opposite to that of the fair‐weather electric field. In this study, we performed theoretical predictions of electric fields in wind‐blown sand transport by assuming a constant charge‐to‐mass ratio (i.e., − 60µc kg− 1) of the saltating particles and considering the streamwise spatial variation of particle concentration in the evolution of wind‐blown sand. Our results show that there exist both vertical and horizontal electric fields in wind‐blown sand transport. The numerical results of vertical electric fields and mass flux are in good agreement with the experimental data measured by Schmidt et al. [1998] and Shao and Raupach [1992], respectively, which suggests that our model is valid. The horizontal electric field demonstrates a vertical stratification feature and is about one order of magnitude bigger than the fair‐weather electric field. Finally, the effects of the wind speed and the sand grain diameter on electric fields are discussed.
The relation between atmospheric humidity and temperature trends for stratospheric water
Authors: Fueglistaler S. , Liu Y.S. , Flannaghan T.J. , Haynes P.H. , Dee D.P. , Read W.J. , Remsberg E.E. , Thomason L.W. , Hurst D.F. , Lanzante J.R. , Bernath P.F.
Published: April 2013

We analyze the relation between atmospheric temperature and water vapor—a fundamental component of the global climate system—for stratospheric water vapor (SWV). We compare measurements of SWV (and methane where available) over the period 1980–2011 from NOAA balloon‐borne frostpoint hygrometer (NOAA‐FPH), SAGE II, Halogen Occultation Experiment (HALOE), Microwave Limb Sounder (MLS)/Aura, and Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE‐FTS) to model predictions based on troposphere‐to‐stratosphere transport from ERA‐Interim, and temperatures from ERA‐Interim, Modern Era Retrospective‐Analysis (MERRA), Climate Forecast System Reanalysis (CFSR), Radiosonde Atmospheric Temperature Products for Assessing Climate (RATPAC), HadAT2, and RICHv1.5. All model predictions are dry biased. The interannual anomalies of the model predictions show periods of fairly regular oscillations, alternating with more quiescent periods and a few large‐amplitude oscillations. They all agree well (correlation coefficients 0.9 and larger) with observations for higher‐frequency variations (periods up to 2–3 years). Differences between SWV observations, and temperature data, respectively, render analysis of the model minus observation residual difficult. However, we find fairly well‐defined periods of drifts in the residuals. For the 1980s, model predictions differ most, and only the calculation with ERA‐Interim temperatures is roughly within observational uncertainties. All model predictions show a drying relative to HALOE in the 1990s, followed by a moistening in the early 2000s. Drifts to NOAA‐FPH are similar (but stronger), whereas no drift is present against SAGE II. As a result, the model calculations have a less pronounced drop in SWV in 2000 than HALOE. From the mid‐2000s onward, models and observations agree reasonably, and some differences can be traced to problems in the temperature data. These results indicate that both SWV and temperature data may still suffer from artifacts that need to be resolved in order to answer the question whether the large‐scale flow and temperature field is sufficient to explain water entering the stratosphere.
Aerosol climatology at Delhi in the western Indo‐Gangetic Plain: Microphysics, long‐term trends, and source strengths
Authors: Lodhi Neelesh K. , Beegum S. Naseema , Singh Sachchidanand , Kumar Krishan
Published: April 2013

We present the climatology of aerosol microphysics, its trends, and impact of potential sources based on the long term measurements (for a period of 11.5 years from December 2001 to May 2012) of aerosol optical depths (AOD) in the spectral range 340–1020 nm from an urban center Delhi (28.6°N, 77.3°E, 238 m mean sea level) in the western Indo‐Gangetic Plain (IGP). The study is the first ever long‐term characterization of aerosols over the western IGP from the ground‐based measurements. AODs are known to affect the air quality, visibility, radiative balance, and cloud microphysics of the region and IGP is one of the highest populated and polluted regions of the world. Our measurements show consistently high AOD during the entire period of observation. The seasonal variations of spectral AODs and Angstrom parameters are generally consistent every year. The AODs show a weak but statistically significant (in 95% confidence level) decreasing trend approximately −0.02/year at 500 nm, possibly, modulated by the pre‐monsoon heavy dust loading during the first half of the observation period. The climatological monthly mean AOD at shorter wavelengths peaks twice, during June and November, while at longer wavelengths it shows only one peak in June. The annual variations of Angstrom exponent, α and its derivative, α′ suggest the prevalence of multi‐modal aerosol size distributions at Delhi. The coarse‐mode aerosols dominate during summer (March–June) and monsoon (July–September) seasons, whereas fine/accumulation mode enhances during post‐monsoon (October–November) and winter (December–February) seasons. Potential advection pathways have been identified using concentration weighted trajectory (CWT) analysis of the 5 day isentropic air mass back trajectories at the observation site and their seasonal variations are discussed.
Comparisons of mercury sources and atmospheric mercury processes between a coastal and inland site
Authors: Cheng Irene , Zhang Leiming , Blanchard Pierrette , Dalziel John , Tordon Rob , Huang Jiaoyan , Holsen Thomas M.
Published: April 2013

Comparisons of mercury sources and atmospheric mercury processes were conducted between a coastal and inland site in northeastern North America. Identifying sources of atmospheric Hg is essential for understanding what is potentially contributing to Hg bioaccumulation at these two sites. A data set consisting of gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), particle‐bound mercury, ozone, trace gases, particulate ions, and meteorological data were analyzed using principal components analysis (PCA), absolute principal component scores (APCS), and back trajectories. The PCA factors representing gaseous Hg condensation on particles during winter and combustion and industrial sources were found at both sites. However, the PCA factor for combustion/industrial sources was not found in 2010 at either site, likely because of SO2 emissions reductions from coal utilities from 2008 to 2010. Using APCS and back trajectories, the combustion/industrial factor at the coastal site was narrowed down to shipping ports along the Atlantic coast. Hg sources affecting coastal sites are different from those affecting inland sites because of the influence of marine airflows. GEM evasion from the ocean was evident from a PCA factor containing GEM, relative humidity, wind speed, and precipitation along with significantly higher contributions of this source (APCS) from oceanic trajectories compared to land/coastal trajectories. Analysis of the effects of ozone and water vapor mixing ratio on %GOM/total gaseous mercury suggest that Hg‐Br photochemistry occurred at lower ozone concentrations (<40 ppb) at the coastal site and the absence of free troposphere transport of GOM.
Automated retrievals of volcanic ash and dust cloud properties from upwelling infrared measurements
Authors: Pavolonis Michael J , Heidinger Andrew K. , Sieglaff Justin
Published: April 2013

A fully automated, globally applicable algorithm to retrieve ash and dust cloud properties from infrared satellite measurements is presented. The algorithm, which will serve as the official operational algorithm of the next generation Geostationary Operational Environmental Satellite (GOES‐R), utilizes an optimal estimation framework that allows uncertainties in the measurements and forward model to be taken into account and uncertainty estimates for each of the retrieved parameters to be determined. The retrieval approach is globally applicable because background atmospheric water vapor, surface temperature, and surface emissivity are explicitly accounted for on a pixel‐by‐pixel basis. The retrieval is demonstrated using the Spinning Enhanced Visible and Infrared Imager (SEVIRI) on‐board the Second Generation Meteosat. Ash clouds from the 2010 eruption of Eyjafjallajökull in Iceland and the 2010 eruption of Soufriere Hills in the eastern Caribbean and a Saharan dust cloud were analyzed, and the accuracy of the retrieval was evaluated using spaceborne lidar measurements. The validation analysis shows that the retrieved ash/dust cloud height, cloud emissivity, and effective particle radius generally agrees well with lidar measurements, especially when volcanic ash clouds are assumed to be composed of andesite and dust clouds composed of kaolinite.
Observations of the atmospheric boundary layer height under marine upstream flow conditions at a coastal site
Authors: Peña A. , Gryning S.‐E. , Hahmann A.N.
Published: April 2013

We investigate several lidar‐type instruments and methodologies for boundary layer height (BLH) estimation during 2 days at a coastal site for winds that experience marine upstream flow conditions. Wavelet and profile fitting procedures on the aerosol backscatter signals from a ceilometer and an aerosol lidar reveal similar BLHs, but their agreement depends on the presence of clouds and the instrument signal, among others. BLHs derived by a threshold on the carrier‐to‐noise profiles of a wind lidar agree well with those derived by using a threshold on the backscatter profile of the ceilometer and are used as reference for a 10 day BLH intercomparison. Furthermore, the BLHs from the aerosol analysis are comparable to those derived from wind speed and direction profiles from combined mast/wind lidar measurements. The BLH derived from simulations performed with the Weather Research and Forecasting (WRF) model shows similar behavior compared to the lidar observations. The seasonal diurnal variation of the BLH for 2010, derived from the wind lidar and ceilometer thresholds, shows similar BLHs but generally higher values compared to that from WRF. No clear BLH diurnal variation is observed neither from the observations nor from the WRF model outputs, except in summer for the latter. Both observations and WRF model simulations reveal higher BLHs during autumn compared to spring time. These BLHs are used to evaluate the intra‐annual variation and show high peaks in September, November, and February.
Stochastic seasonality of rainfall in New Zealand
Authors: Sansom John , Thomson Peter , Carey‐Smith Trevor
Published: April 2013

Seasonality is an important source of variation in many processes and needs to be incorporated into rainfall models. The stochastic seasonal rainfall models for high temporal resolution data [Sansom and Thomson, 2010] and daily data (T. Carey‐Smith et al., A hidden seasonal switching model for multisite daily rainfall, manuscript in preparation 2012) both depend on the specification of one day of the year for each season being in the particular season. So, if the seasonality is to be represented by four seasons then it is necessary to provide four dates on each of which it can be said that, every year, the season is of the first, second, third or fourth type respectively on that day of the year. The model fitting can only proceed once these dates, the mid‐seasons, have been provided.

In a region of large seasonal rainfall variation the determination of these mid‐seasons would not be difficult and the model fitting not sensitive to their choice. However, although it is clearly evident in the annual pattern of monthly accumulations, New Zealand's rainfall seasonality is not strong and careful assessment of the mid‐season dates is necessary. They need to be estimated with a precision of days and the 55‐year long rainfall records of daily data from 141 stations spread across New Zealand were analysed on a regional basis. The analysis found regionally coherent dates when the mean daily rain rate changed significantly and that over the years these dates could be modelled as a four component von Mises distribution with characteristics consistent with stochastic seasonality.
ENSO dynamics: Low‐dimensional‐chaotic or stochastic?
Authors: Živković T. , Rypdal K.
Published: April 2013

We apply a test for deterministic, low‐dimensional, and nonlinear dynamics to the Niño 3 time series for the El Niño Southern Oscillation (ENSO). The test is positive if the time series includes the seasonal variation, but negative if it only represents the anomaly, i.e., the deviation from the seasonal cycle. The results indicate that deterministic, low‐dimensional, and nonlinear dynamics in ENSO is associated with the seasonal cycle, and that the dynamics determining the interannual timing and strength of El Niño/La Niña episodes is high‐dimensional/stochastic. Application of stochastic forcing to a time‐delay equation for equatorial‐wave dynamics can reproduce stochastic dynamics and other important aspects of ENSO. Without such stochastic forcing, this model yields deterministic, low‐dimensional dynamics. With stochastic forcing, our test still yields such dynamics if the seasonal cycle is retained, but does not if the annual cycle is subtracted before the test is applied. The model results illustrate that the seasonal variability can be governed by low‐dimensional nonlinear dynamics, while the interannual variability associated with ENSO is dominated by the stochastic forcing.
Observations of Quasi‐Two‐Day wave by TIMED/SABER and TIMED/TIDI
Authors: Gu Sheng‐Yang , Li Tao , Dou Xiankang , Wu Qian , Mlynczak M. G. , Russell J. M.
Published: April 2013

Seasonal and interannual variations of the Quasi‐Two‐Day wave s = −3 (W3) and s = −4 (W4) modes were studied with global temperature and wind data sets during 2002–2012, observed respectively by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) and TIMED Doppler Imager (TIDI) instruments onboard the Thermosphere Ionosphere and Mesosphere Electric Dynamics (TIMED) satellite. The amplitudes of W3 and W4 are significantly enhanced during austral and boreal summer respectively. Strong W3 amplitudes are observed during January 2006 in all three components of temperature, meridional wind, and zonal wind. This is most likely related to the intensive winter planetary wave activity that led to a strong sudden stratosphere warming (SSW) event. The maximum amplitudes of W4 during the 10 years are ~8–9 K, ~40 m/s, and ~20 m/s for temperature, meridional, and zonal components respectively, nearly half as large as those of W3, with ~15 K, ~65 m/s, and ~35 m/s. In January 2008 and 2009, unusually weak W3 but strong W4 oscillations were observed, corresponding to the much weaker summer easterly jets (westward wind) than those in other years. This suggests that relatively weak summer easterly may not be able to provide sufficiently strong barotropic/baroclinic instability to amplify W3 but is favorable for the amplification of W4. The weaker magnitude values, lower peak heights, and longer life intervals of W4 than those of W3 suggest that the W4 may suffer a greater damping rate than the W3. The observations of W4 show good agreement with Rossby‐gravity (4, 0) mode, which is more easily trapped in both latitude and altitude because of its lower group velocity than that of Rossby‐gravity (3, 0) mode.
Dynamical prediction of the East Asian winter monsoon by the NCEP Climate Forecast System
Authors: Jiang Xingwen , Yang Song , Li Yueqing , Kumar Arun , Wang Wanqiu , Gao Zongting
Published: April 2013

The National Centers for Environmental Prediction (NCEP) Climate Forecast System (CFS) provides important source of information on seasonal climate prediction for many Asian countries that are affected by monsoon. In this study, the authors provide a comprehensive assessment of the prediction of East Asian winter monsoon (EAWM) by the CFS version 2 (CFSv2) using the hindcast for 1983–2010, with a focus on seasonal–interannual time scales. Output from the Atmospheric Model Intercomparison Project (AMIP) and the Coupled Model Intercomparison Project (CMIP) simulations is also analyzed to understand the physical process of monsoon. Several major features of the EAWM are well predicted by the CFSv2. Particularly, the EAWM‐related atmospheric circulation and surface climate over oceans are well predicted several months in advance, and the prediction over oceans is better than that over land. While the CFSv2 has low skill in predicting the Arctic Oscillation (AO), it well predicts El Niño‐Southern Oscillation (ENSO) and its impact on the EAWM, contributing to the decent prediction of EAWM. Comparisons among hindcast, AMIP, and CMIP indicate that ocean–atmosphere coupling is important for EAWM prediction. While the EAWM in AMIP is weaker, CMIP predicts more realistic monsoon features. The enhanced performance of CMIP is partly attributed to its better simulation of precipitation over the western Maritime Continent (MC). All three types of experiments fail to depict the relationship between EAWM and AO and simulate a stronger‐than‐observed response of EAWM to ENSO. Improving the simulation of convection over the MC potentially enhances the skill of CFSv2 in predicting the EAWM.
Retrieval and validation of global, direct, and diffuse irradiance derived from SEVIRI satellite observations
Authors: Greuell W. , Meirink J. F. , Wang P.
Published: April 2013

This paper discusses Surface Insolation under Clear and Cloudy skies derived from SEVIRI imagery (SICCS), a physics‐based, empirically adjusted algorithm developed for estimation of surface solar irradiance from satellite data. Its most important input are a cloud mask product and cloud properties derived from Meteosat/Spinning Enhanced Visible and Infrared Imager (SEVIRI) observations. These observations set the characteristics of the output, namely, a temporal resolution of 15 min, a nadir spatial resolution of 3 × 3 km2, the period from January 2004 until at least November 2012, and the domain equal to most of the Meteosat disc. SICCS computes global, direct, and diffuse irradiance separately. Direct irradiance for cloudy skies is estimated with an empirical method. Hourly means retrieved with SICCS were validated with data from eight Baseline Surface Radiation Network stations for the year 2006. We found median values of the station biases of +6 W/m2 (+5%) for direct irradiance, +1 W/m2 (+1%) for diffuse irradiance, and +7 W/m2 (+2%) for global irradiance. Replacing the three‐hourly aerosol optical thickness input by monthly means introduces considerable additional biases in the clear‐sky direct (−6%) and diffuse (+26%) irradiances. The performance of SICCS does not degrade when snow covers the surface. Biases do not vary with cloud optical thickness and cloud particle radius. However, the bias in global transmissivity tends to decrease with increasing cloud heterogeneity, and the bias in direct transmissivity is a function of the solar zenith angle. We discuss why satellite retrieval of surface solar irradiance is relatively successful.
Microphysical simulations of large volcanic eruptions: Pinatubo and Toba
Authors: English Jason M. , Toon Owen B. , Mills Michael J.
Published: April 2013

Simulations of stratospheric clouds from eruptions ranging in size from the 1991 eruption of Mount Pinatubo to that of Toba 74,000 years ago have been completed using a 3D microphysical sectional aerosol model advectively coupled to a general circulation model with prognostic chemistry (Whole Atmosphere Community Climate Model/Community Aerosol and Radiation Model for Atmospheres). For Pinatubo, properties of the aerosol cloud peak within the ranges derived from observations in the Northern Hemisphere, but reduce faster than observed, and a general low bias is found in the Southern Hemisphere. These biases could be reduced by adding aerosol radiative coupling, a quasi‐biennial oscillation, and the Cerro Hudson eruption to the model. Simulations of eruptions 10 times and 100 times larger than Pinatubo suggest burdens and Aerosol Optical Depth increase less than linearly (a 100‐fold injection increase produces a 20‐fold AOD increase) due to particle growth and sedimentation, consistent with previous work that also found the radiative forcings from large eruptions to be self‐limiting. Global‐averaged AOD remains elevated for 1, 2, and 4 years, respectively, for the three simulated eruptions. The inclusion of van der Waals forces in our coagulation scheme increases peak effective radius and reduces peak AOD by about 10–20%, with bigger effects for larger eruptions. Our simulations find peak mode size to vary by up to an order of magnitude and mode width to vary by up to 50%, suggesting that two‐moment modal models may not accurately capture the evolving size distribution. These simulations suggest the value of including van der Waals forces in the coagulation scheme and sectional size distributions in climate models.
Impact of dataset choice on calculations of the short‐term cloud feedback
Authors: Dessler A. E. , Loeb N.G.
Published: April 2013

Dessler [2010, hereafter D10] estimated the magnitude of the cloud feedback in response to short‐term climate variations and concluded that it was likely positive, with an average magnitude of +0.50 ± 0.75 W/m2/K. This paper investigates the sensitivity of D10's results to the choice of clear‐sky top‐of‐atmosphere flux (ΔRclear‐sky), surface temperature (ΔTs), and reanalysis data sets. Most of the alternative ΔRclear‐sky data sets produce cloud feedbacks that are close to D10, differing by 0.2–0.3 W/m2/K. An exception is the Terra SSF1deg ΔRclear‐sky product, which produces an overall negative cloud feedback. However, a critical examination of those data leads us to conclude that that result is due to problems in the Terra ΔRclear‐sky arising from issues with cloud clearing prior to July 2001. Eliminating the problematic early portion yields a cloud feedback in good agreement with D10. We also present an alternative calculation of the cloud feedback that does not require an estimate of ΔRclear‐sky, and this calculation also produces a positive cloud feedback in agreement with D10. The various ΔTs data sets produce cloud feedbacks that differ by as much as 0.8 W/m2/K. The choice of reanalysis, used as a source of ΔRclear‐sky or as adjustments for the cloud radiative forcing, has a small impact on the inferred cloud feedback. Overall, these results confirm the robustness of D10's estimate of a likely positive feedback.
Climate extremes indices in the CMIP5 multimodel ensemble: Part 1. Model evaluation in the present climate
Authors: Sillmann J. , Kharin V. V. , Zhang X. , Zwiers F. W. , Bronaugh D.
Published: April 2013

This paper provides a first overview of the performance of state‐of‐the‐art global climate models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5) in simulating climate extremes indices defined by the Expert Team on Climate Change Detection and Indices (ETCCDI), and compares it to that in the previous model generation (CMIP3). For the first time, the indices based on daily temperature and precipitation are calculated with a consistent methodology across multimodel simulations and four reanalysis data sets (ERA40, ERA‐Interim, NCEP/NCAR, and NCEP‐DOE) and are made available at the ETCCDI indices archive website. Our analyses show that the CMIP5 models are generally able to simulate climate extremes and their trend patterns as represented by the indices in comparison to a gridded observational indices data set (HadEX2). The spread amongst CMIP5 models for several temperature indices is reduced compared to CMIP3 models, despite the larger number of models participating in CMIP5. Some improvements in the CMIP5 ensemble relative to CMIP3 are also found in the representation of the magnitude of precipitation indices. We find substantial discrepancies between the reanalyses, indicating considerable uncertainties regarding their simulation of extremes. The overall performance of individual models is summarized by a “portrait” diagram based on root‐mean‐square errors of model climatologies for each index and model relative to four reanalyses. This metric analysis shows that the median model climatology outperforms individual models for all indices, but the uncertainties related to the underlying reference data sets are reflected in the individual model performance metrics.
Reassessing the variability in atmospheric H2 using the two‐way nested TM5 model
Authors: Pieterse G. , Krol M. C. , Batenburg A. M. , M. Brenninkmeijer C. A. , Popa M. E. , O'Doherty S. , Grant A. , Steele L. P. , Krummel P. B. , Langenfelds R. L. , Wang H. J. , Vermeulen A. T. , Schmidt M. , Yver C. , Jordan A. , Engel A. , Fisher R. E. , Lowry D. , Nisbet E. G. , Reimann S. , Vollmer M. K. , Steinbacher M. , Hammer S. , Forster G. , Sturges W. T. , Röckmann T.
Published: April 2013

This work reassesses the global atmospheric budget of H2 with the TM5 model. The recent adjustment of the calibration scale for H2 translates into a change in the tropospheric burden. Furthermore, the ECMWF Reanalysis‐Interim (ERA‐Interim) data from the European Centre for Medium‐Range Weather Forecasts (ECMWF) used in this study show slower vertical transport than the operational data used before. Consequently, more H2 is removed by deposition. The deposition parametrization is updated because significant deposition fluxes for snow, water, and vegetation surfaces were calculated in our previous study. Timescales of 1–2 h are asserted for the transport of H2 through the canopies of densely vegetated regions. The global scale variability of H2 and δ[DH2] is well represented by the updated model. H2 is slightly overestimated in the Southern Hemisphere because too little H2 is removed by dry deposition to rainforests and savannahs. The variability in H2 over Europe is further investigated using a high‐resolution model subdomain. It is shown that discrepancies between the model and the observations are mainly caused by the finite model resolution. The tropospheric burden is estimated at 165±8 Tg H2. The removal rates of H2 by deposition and photochemical oxidation are estimated at 53±4 and 23±2 Tg H2/yr, resulting in a tropospheric lifetime of 2.2±0.2 year.
Effects of the Tibetan Plateau on the onsetof the summer monsoon in South Asia: The role of the air‐sea interaction
Authors: Abe Manabu , Hori Masatake , Yasunari Tetsuzo , Kitoh Akio
Published: April 2013

Using both a coupled atmosphere‐ocean general circulation model (GCM) and an atmospheric GCM, we investigate the effects of the Tibetan Plateau (TP) on the onset of the South Asian summer monsoon by conducting simulations with and without the TP. In the coupled GCM, the presence of the TP causes the monsoon onset to occur approximately 15 days later in the Arabian Sea (AS) and India (ID) and approximately 10 days earlier in the Bay of Bengal (BB). These changes are attributed to different atmospheric circulation patterns and different conditions within the adjacent oceans, such as the AS and the BB. When the TP is included, lower sea surface temperatures (SSTs) in the AS contribute to a stable lower atmosphere, which suppresses convection over the AS and ID in May. In contrast, low pressure over South Asia, caused by the TP, induces a southwesterly toward the BB that transports a substantial amount of water vapor to the BB. This flow results in an earlier monsoon in the BB. Without the TP, higher SSTs that are formed in the AS in May destabilize the lower atmosphere and create a depression, resulting in an earlier onset of the monsoon over the AS and ID. Consequently, the cyclonic circulation spreads abruptly to the BB, and precipitation begins to increase over the BB. Therefore, the air‐sea interaction in the adjacent ocean under the influence of the TP strongly modulates the onset of the South Asian summer monsoon. This modulation was verified by the atmospheric GCM experiments.
Meteorology and dust in the central Sahara: Observations from Fennec supersite‐1 during the June 2011 Intensive Observation Period
Authors: Marsham J. H. , Hobby M. , Allen C. J. T. , Banks J. R. , Bart M. , Brooks B. J. , Cavazos‐Guerra C. , Engelstaedter S. , Gascoyne M. , Lima A. R. , Martins J. V. , McQuaid J. B. , O'Leary A. , Ouchene B. , Ouladichir A. , Parker D. J. , Saci A. , Salah‐Ferroudj M. , Todd M. C. , Washington R.
Published: April 2013

We describe observations from the Fennec supersite at Bordj Badji Mokhtar (BBM) made during the June 2011 Fennec Intensive Observation Period. These are the first detailed in situ observations of meteorology and dust from the central Sahara, close to the center of the Saharan heat low and the summertime dust maximum. Historically, a shortage of such Saharan observations has created problems for evaluating processes, models, and remote sensing. There was a monsoon influence at BBM before 8 June and after 12 June, with dry Harmattan winds in between. A split boundary layer, generated by ventilation from the Atlantic, persisted during the drier phase. Extensive cold pools (haboobs) and microburst‐type events were regularly observed. Moisture reached BBM at night from the monsoon and the embedded haboobs. As well as the regularly occurring nocturnal low‐level jet (LLJ), a Saharan upper boundary layer (650 hPa) jet was observed, where winds feel drag from dry convection in the afternoon. This jet is linked to the diurnal cycles of moisture and cloud. Most dust was observed in the cloudier monsoon‐affected periods, and covarying dust and cloud amounts explain most of the variations in shortwave radiation that control the surface sensible flux. Dustiness is related to a standard parameterization of uplift using 10 m winds (“uplift potential”), and this is used to estimate uplift. Around 50% of uplift is nocturnal. Around 30% is from the LLJ, and 50% is from haboobs, which are mainly nocturnal. This demonstrates, for the first time from observations, the key role of haboobs, which are problematic for models.
Classification of convective/stratiform echoes in radar reflectivity observations using a fuzzy logic algorithm
Authors: Yang Yi , Chen Xin , Qi Youcun
Published: April 2013

In radar reflectivity observations, the convective and stratiform rain types always have poorly defined boundaries, which caused problem for rain classification. A fuzzy logic (FL) algorithm is developed to classify convective and stratiform rainfall based on the radar reflectivity observations in the next three steps: First, the algorithm is calibrated on Hefei Doppler radar site in China. Four features are selected based on a dataset for calibration, which spanned the period from 29 June to 23 July 2003; and the features basically represent a subjective choice of characteristics that are expected to distinguish different rain types. In the second step, membership functions are used to determine the degree to which each feature belongs to each rain type in the fuzzification process. Finally, the degree of fuzzification for each input feature is multiplied by predetermined weighting coefficients. The weighted degrees of the fuzzification are aggregated to produce a single value for each rain type. The aggregation can represent the possibility of classified rainfall type, and larger value reveals the higher potential for a particular class. The FL algorithm has been applied to four typical independent individual cases collected by Hefei Doppler radar, which have not been included in the database for calibration. Results show that the classification using the proposed FL algorithm is physically reasonable according to the analysis of three‐dimensional radar reflectivity patterns, implying that the proposed FL algorithm has a great potential for the precipitation classification.
Data‐driven regionalization of river discharges and emergent land cover–evapotranspiration relationships across Sweden
Authors: van der Velde Ype , Lyon Steve W. , Destouni Georgia
Published: April 2013

Changes in river discharge and river water quality, due to climate change and other drivers such as land cover change, pose both societal and ecosystem threats. Analyses of measured terrestrial river fluxes are key for identifying the drivers and quantifying the magnitudes of such riverine changes. In this paper, we develop and apply a data‐driven regionalization approach using the dense network of discharge measurements in Sweden. The developed regionalization approach facilitates detailed mapping of discharges (Q) and change trends in Q across Sweden. Combining these with estimates of precipitation (P) and change trends in P, we estimated actual evapotranspiration (AET) and change trends in AET via catchment‐scale water balance constraints. We identified characteristic land cover–evapotranspiration relationships by plotting water use efficiency (AET/P) against energy use efficiency (AET/potential ET) for areas with unique land cover across Sweden. Our results show that wetlands have clearly lower water and energy use efficiencies compared to open waters, forests, and agriculture, and that agriculture has water and energy use efficiencies closest to those of open waters. We further compared the data‐driven regionalization estimates of different water balance components with estimates of regional climate models (RCMs). The RCMs do not describe well the observed change trends in Sweden. In particular, for evapotranspiration, the observed change trends are not reproduced by any of the investigated 24 RCMs.
Evaluation of Whole Atmosphere Community Climate Model simulations of ozone during Arctic winter 2004–2005
Authors: Brakebusch M. , Randall C. E. , Kinnison D. E. , Tilmes S. , Santee M. L. , Manney G. L.
Published: April 2013

The work presented here evaluates polar stratospheric ozone simulations from the Whole Atmosphere Community Climate Model (WACCM) for the Arctic winter of 2004–2005. We use the Specified Dynamics version of WACCM (SD‐WACCM), in which temperatures and winds are nudged to meteorological assimilation analysis results. Model simulations of ozone and related constituents generally compare well to observations from the Earth Observing System Microwave Limb Sounder (MLS). At most times, modeled ozone agrees with MLS data to within ~10%. However, a systematic high bias in ozone in the model of ~18% is found in the lowermost stratosphere in March. We attribute most of this ozone bias to too little heterogeneous processing of halogens late in the winter. We suggest that the model under‐predicts ClONO2 early in the winter, which leads to less heterogeneous processing and too little activated chlorine. Model HCl could also be overestimated due to an underestimation of HCl uptake into supercooled ternary solution (STS) particles. In late winter, the model overestimates gas‐phase HNO3, and thus NOy, which leads to an over‐prediction of ClONO2 (under‐prediction of activated chlorine). A sensitivity study, in which temperatures for heterogeneous chemistry reactions were reduced by 1.5 K, shows significant improvement of modeled ozone. Chemical ozone loss is inferred from the MLS observations using the pseudo‐passive subtraction approach. The inferred ozone loss using this method is in agreement with or less than previous independent results for the Arctic winter of 2004–2005, reaching 1.0 ppmv on average and up to 1.6 ppmv locally in the polar vortex.
A study of the shortwave direct aerosol forcing using ESSP/CALIPSO observation and GCM simulation
Authors: Oikawa Eiji , Nakajima Teruyuki , Inoue Toshiro , Winker David
Published: April 2013

Shortwave direct aerosol radiative forcing (DARF) is derived at the top of the atmosphere (TOA) and at the surface under clear‐sky, cloudy‐sky, and all‐sky conditions using data of space‐borne CALIOP lidar and MODIS sensor. We investigate four scenarios for evaluating the DARF: clear‐sky, the case that aerosols exist above clouds, the case that aerosols exist below high‐level clouds, and the case that aerosols are not detected by CALIOP in cloudy‐sky condition. The cloudy‐sky DARF is estimated by the latter three scenarios. The all‐sky DARF is the combination of clear‐sky and cloudy‐sky DARF weighted by the cloud occurrence. They are then compared with DARF calculated by a global aerosol model, SPRINTARS. The results show that the TOA forcing over desert regions caused by dust with single scattering albedo (SSA) of 0.92 is positive regardless of cloud existence, due to high solar surface albedo. Off southern Africa, smoke aerosols with SSA of 0.84 above low‐level clouds are observed and simulated and the annual mean TOA cloudy‐sky DARF is estimated at more than +3 Wm−2, consistent with past studies. Aerosols with SSA of 0.96 within optically thin clouds cause a TOA negative forcing, while that within optically thick clouds cause a TOA positive forcing. This indicates that aerosols within optically thick clouds cause positive forcing in our radiative transfer calculation, regardless of SSA. Annual zonal averages of DARF from 60°S to 60°N under clear‐sky, cloudy‐sky, and all‐sky are −2.97, +0.07, and −0.61 Wm−2 from CALIOP and −2.78, +1.07, and −0.58 Wm−2 from SPRINTARS.