bluuebunny/crossref_metadata_2025_split huggingface dataset:
Climate‐induced changes in sea salt aerosol number emissions: 1870 to 2100
Authors: Struthers H. , Ekman A. M. L. , Glantz P. , Iversen T. , Kirkevåg A. , Seland Ø. , Mårtensson E. M. , Noone K. , Nilsson E. D. 
Published: April 2013

AbstractGlobal climate model output is combined with an emission parameterization to estimate the change in the global and regional sea salt aerosol number emission from 1870 to 2100. Global average results suggest a general increase in sea salt aerosol number emission due to increasing surface wind speed. However, the emission changes are not uniform over the aerosol size spectrum due to an increase in sea surface temperature. From 1870 to 2100 the emission of coarse mode particles (dry diameter DP>655 nm) increase by approximately 10 % (global average), whereas no significant change in the emission of ultrafine mode aerosols (dry diameter Dp<76 nm) was found over the same period. Significant regional differences in the number emission trends were also found. Based on CAM‐Oslo global climate model output, no straight‐forward relationship was found between the change in the number emissions and changes in the sea salt aerosol burden or optical thickness. This is attributed to a change in the simulated residence time of the sea salt aerosol. For the 21st century, a decrease in the residence time leads to a weaker sea salt aerosol‐climate feedback that what would be inferred based on changes in number emissions alone. Finally, quantifying any potential impact on marine stratocumulus cloud microphysical and radiative properties due to changes in sea salt aerosol number emissions is likely to be complicated by commensurate changes in anthropogenic aerosol emissions and changes in meteorology.
Empirical conversion of the vertical profile of reflectivity from Ku‐band to S‐band frequency
Authors: Cao Qing , Hong Yang , Qi Youcun , Wen Yixin , Zhang Jian , Gourley Jonathan J. , Liao Liang 
Published: April 2013

ABSTRACTThis paper presents an empirical method for converting reflectivity from Ku‐band (13.8 GHz) to S‐band (2.8 GHz) for several hydrometeor species, which facilitates the incorporation of Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) measurements into quantitative precipitation estimation (QPE) products from the U.S. Next‐Generation Radar (NEXRAD). The development of empirical dual‐frequency relations is based on theoretical simulations, which have assumed appropriate scattering and microphysical models for liquid and solid hydrometeors (raindrops, snow, and ice/hail). Particle phase, shape, orientation, and density (especially for snow particles) have been considered in applying the T‐matrix method to compute the scattering amplitudes. Gamma particle size distribution (PSD) is utilized to model the microphysical properties in the ice region, melting layer, and raining region of precipitating clouds. The variability of PSD parameters is considered to study the characteristics of dual‐frequency reflectivity, especially the variations in radar dual‐frequency ratio (DFR). The empirical relations between DFR and Ku‐band reflectivity have been derived for particles in different regions within the vertical structure of precipitating clouds. The reflectivity conversion using the proposed empirical relations has been tested using real data collected by TRMM‐PR and a prototype polarimetric WSR‐88D (Weather Surveillance Radar 88 Doppler) radar, KOUN. The processing and analysis of collocated data demonstrate the validity of the proposed empirical relations and substantiate their practical significance for reflectivity conversion, which is essential to the TRMM‐based vertical profile of reflectivity correction approach in improving NEXRAD‐based QPE.
Monitoring scan asymmetry of microwave humidity sounding channels using simultaneous all angle collocations (SAACs)
Authors: John Viju O. , Holl Gerrit , Atkinson Nigel , Buehler Stefan A. 
Published: April 2013

AbstractSimultaneous all angle collocations (SAACs) of microwave humidity sounders (AMSU‐B and MHS) on‐board polar orbiting satellites are used to estimate scan‐dependent biases. This method has distinct advantages over previous methods, such as that the estimated scan‐dependent biases are not influenced by diurnal differences between the edges of the scan and the biases can be estimated for both sides of the scan. We find the results are robust in the sense that biases estimated for one satellite pair can be reproduced by double differencing biases of these satellites with a third satellite. Channel 1 of these instruments shows the least bias for all satellites. Channel 2 has biases greater than 5 K, thus needs to be corrected. Channel 3 has biases of about 2 K and more and they are time varying for some of the satellites. Channel 4 has the largest bias which is about 15 K when the data are averaged for 5 years, but biases of individual months can be as large as 30 K. Channel 5 also has large and time varying biases for two of the AMSU‐Bs. NOAA‐15 (N15) channels are found to be affected the most, mainly due to radio frequency interference (RFI) from onboard data transmitters. Channel 4 of N15 shows the largest and time varying biases, so data of this channel should only be used with caution for climate applications. The two MHS instruments show the best agreement for all channels. Our estimates may be used to correct for scan‐dependent biases of these instruments, or at least used as a guideline for excluding channels with large scan asymmetries from scientific analyses.
A climatology of frozen‐in anticyclones in the spring arctic stratosphere over the period 1960–2011
Authors: Thiéblemont Rémi , Orsolini Yvan J. , Hauchecorne Alain , Drouin Marc‐Antoine , Huret Nathalie 
Published: April 2013

During springtime, following the stratospheric final warming, intrusions from low latitudes can become trapped at polar latitudes in long‐lived anticyclones. Such “frozen‐in” anticyclones (FrIACs) have occasionally been observed to persist as late as August, advected by summer easterlies.In this study, the high‐resolution advection contour model MIMOSA is used to advect a pseudo‐potential vorticity tracer. The model is driven by ERA‐40 and the ERA‐Interim reanalyses over the period 1960–2011. We first identify a remarkable FrIAC event in spring 2011. In addition, we developed a method to detect the characteristic size of low‐latitude intrusions into the polar region at the time of the spring transition, over the period 1960–2011. Years are classified as either Type‐A when the intrusions are small or as Type‐B when intrusions are large, potentially evolving into FrIACs. For a FrIAC to occur, we require an additional criterion based on the in‐phase character of the core of the intrusions and the anticyclone.During the 52 analyzed years, 9 events have been identified: 1 in the 1960s, 1 in the 1980s, 2 in the 1990s, and 5 from 2002. FrIAC are predominantly long‐lived intrusions, which occur in association with abrupt and early reversal to summer easterlies with a large heat flux pulse around the date of this wind reversal. Finally, the results are discussed in a climatological context.
Detecting snowfall over land by satellite high‐frequency microwave observations: The lack of scattering signature and a statistical approach
Authors: Liu Guosheng , Seo Eun‐Kyoung 
Published: April 2013

AbstractIt has been long believed that the dominant microwave signature of snowfall over land is the brightness temperature decrease caused by ice scattering. However, our analysis of multiyear satellite data revealed that on most of occasions, brightness temperatures are rather higher under snowfall than nonsnowfall conditions, likely due to the emission by cloud liquid water. This brightness temperature increase masks the scattering signature and complicates the snowfall detection problem. In this study, we propose a statistical method for snowfall detection, which is developed by using CloudSat radar to train high‐frequency passive microwave observations. To capture the major variations of the brightness temperatures and reduce the dimensionality of independent variables, the detection algorithm is designed to use the information contained in the first three principal components resulted from Empirical Orthogonal Function (EOF) analysis, which capture ~99% of the total variances of brightness temperatures. Given a multichannel microwave observation, the algorithm first transforms the brightness temperature vector into EOF space and then retrieves a probability of snowfall by using the CloudSat radar‐trained look‐up table. Validation has been carried out by case studies and averaged horizontal snowfall fraction maps. The result indicated that the algorithm has clear skills in identifying snowfall areas even over mountainous regions.
Identification and ranking of extraordinary rainfall events over Northwest Italy: The role of Atlantic moisture
Authors: Pinto Joaquim G. , Ulbrich Sven , Parodi Antonio , Rudari Roberto , Boni Giorgio , Ulbrich Uwe 
Published: April 2013

AbstractAn objective identification and ranking of extraordinary rainfall events for Northwest Italy is established using time series of annual precipitation maxima for 1938–2002 at over 200 stations. Rainfall annual maxima are considered for five reference durations (1, 3, 6, 12, and 24 h). In a first step, a day is classified as an extraordinary rainfall day when a regional threshold calculated on the basis of a two‐components extreme value distribution is exceeded for at least one of the stations. Second, a clustering procedure taking into account the different rainfall durations is applied to the identified 163 events. Third, a division into six clusters is chosen using Ward's distance criteria. It is found that two of these clusters include the seven strongest events as quantified from a newly developed measure of intensity which combines rainfall intensities and spatial extension. Two other clusters include the weakest 72% historical events. The obtained clusters are analyzed in terms of typical synoptic characteristics. The two top clusters are characterized by strong and persistent upper air troughs inducing not only moisture advection from the North Atlantic into the Western Mediterranean but also strong northward flow towards the southern Alpine ranges. Humidity transports from the North Atlantic are less important for the weaker clusters. We conclude that moisture advection from the North Atlantic plays a relevant role in the magnitude of the extraordinary events over Northwest Italy.
Optical power and energy radiated by natural lightning
Authors: Quick Mason G. , Krider E. Philip 
Published: April 2013

AbstractCalibrated measurements of the visible and near‐infrared radiation produced by both negative and positive cloud‐to‐ground (CG) lightning strokes have been made at distances of 5 to 32 km in southern Arizona (AZ) and the central Great Plains using a photodiode sensor with a flat spectral response between 0.4 and 1.0 µm. Time‐correlated video images (60 fps) of the channel development provided information about the types of strokes that were detected and reports from the U.S. National Lightning Detection Network indicated their locations, polarities, and estimates of their peak current. In our sample of negative strokes that were suitable for analysis, there were 23 first (or only) strokes (FS), 19 subsequent strokes that created new ground contacts (NGC), and 101 subsequent strokes that re‐illuminated a preexisting channel (PEC). We also analyzed 10 positive strokes (in nine flashes), and 73 of the larger impulses that were radiated by intracloud discharges (CPs). Assuming that these events can be approximated as isotropic sources and that the effects of atmospheric extinction are negligible, the peak optical power (Po), total optical energy (Eo), and characteristic widths of the sources (tcw = Eo/Po) have been computed. Median values of Po for negative FS, NGC, and PEC strokes were 1.8 × 1010 W, 1.1 × 1010 W, and 4.4 × 109 W, respectively. Median values of Eo were 3.6 × 106 J, 3.5 × 106 J, and 1.2 × 106 J, respectively. The median characteristic widths of negative FS, NGC, and PEC strokes were 229 µs, 244 µs, and 283 µs, respectively. Positive CG strokes produced a median Po, Eo, and tcw of 1.9 × 1010 W, 9.3 × 106 J, and 497 µs, respectively. Estimates of the space‐and‐time‐average power per unit length () in the lower portion of negative FS, NGC, and PEC channels had medians of 2.8 × 106 W/m, 3.2 × 106 W/m, and 1.4 × 106 W/m, respectively, and the median for four positive strokes was 8.8 × 106 W/m. Median values for the estimated peak electromagnetic power (PEM) radiated at early times in the strokes are 2.0 × 109 W, 2.5 × 109 W, 1.0 × 109 W, and 9.1 × 109 W for FS, NGC, PEC and positive strokes, respectively. CP events produced a median Po, Eo, and tcw of 2.0 × 109 W, 0.7 × 106 J, and 311 µs, respectively, and are in good agreement with aircraft and satellite measurements. The values of Po, Eo, and for negative CG strokes in AZ are significantly larger than prior measurements in Florida, likely because there is less atmospheric extinction in our dataset, and due to extinction, all the above values of Po, Eo, and are lower limits at the source.
Aviation‐induced cirrus and radiation changes at diurnal timescales
Authors: Schumann Ulrich , Graf Kaspar 
Published: April 2013

AbstractThe radiative forcing from aviation‐induced cirrus is derived from observations and models. The annual mean diurnal cycle of airtraffic in the North Atlantic region exhibits two peaks in early morning and afternoon with different peak times in the western and eastern parts of the North Atlantic region. The same “aviation fingerprint” is found in 8 years (2004–2011) of Meteosat observations of cirrus cover and OLR. The observations are related to airtraffic data with linear response models assuming the background atmosphere without aviation to be similar to that observed in the South Atlantic. The change in OLR is interpreted as aviation‐induced longwave radiative forcing (LW RF). The data analysis suggests an LW RF of about 600–900 mW m−2 regionally. A detailed contrail cirrus model for given global meteorology and airtraffic in 2006 gives similar results. The global RF is estimated from the ratio of global and regional RF as derived from three models. The extrapolation implies about 100–160 mW m−2 global LW RF. The models show large differences in the shortwave/longwave RF‐magnitude ratio. One model computes a ratio of 0.6, implying an estimate of global net RF of about 50 mW m−2 (40–80 mW m−2). Other models suggest smaller ratios, with less cooling during day, which would imply considerably larger net effects. The sensitivity of the results to the accuracy of the observations, traffic data, and models and the estimated background is discussed.
Nitrous oxide (N2O) emissions from California based on 2010 CalNex airborne measurements
Authors: Xiang Bin , Miller Scot M. , Kort Eric A. , Santoni Gregory W. , Daube Bruce C. , Commane Roisin , Angevine Wayne M. , Ryerson Tom B. , Trainer Michael K. , Andrews Arlyn E. , Nehrkorn Thomas , Tian Hanqin , Wofsy Steven C. 
Published: April 2013

AbstractNitrous oxide (N2O) is an important gas for climate and for stratospheric chemistry, with a lifetime exceeding 100 years. Global concentrations have increased steadily since the 18th century, apparently due to human‐associated emissions, principally from the application of nitrogen fertilizers. However, quantitative studies of agricultural emissions at large spatial scales are lacking, inhibited by the difficulty of measuring small enhancements in atmospheric concentration. Here we derive regional emission rates for N2O in the agricultural heartland of California based on analysis of in‐situ airborne atmospheric observations collected using a new quantum cascade laser spectrometer. The data were obtained on board the NOAA WP‐3 research aircraft during the CalNex (California Research at the Nexus of Air Quality and Climate Change) program in late spring 2010. We coupled the WRF (weather research and forecasting) model, a meso‐scale meteorology model, with the STILT (stochastic time‐inverted Lagrangian transport) model, a Lagrangian particle dispersion model, to link our in‐situ airborne observations to surface emissions. We then used a variety of statistical methods to identify source areas and to optimize emission rates. Our results are consistent with the view that fertilizer application is the largest source of N2O in the Central Valley. The spatial distribution of surface emissions, based on California land use and activity maps, was very different than indicated in the leading emission inventory (EDGAR 4.0). Our estimated total emission flux of N2O for California in May and June was 3 – 4 times larger than the annual mean given for the state by EDGAR and other inventories, indicating a strong seasonal variation. We estimated the statewide total annual emissions of N2O to be 0.042 ± 0.011 Tg N/year, roughly equivalent to inventory values if we account for seasonal variations using observations obtained in the midwestern United States. This state total N2O emission is 20.5 Tg CO2 equivalent (100 year global warming potential = 310 CO2 eq/g N2O), accounting for approximately 4% of the state total greenhouse gas emissions.
The roles of aerosol direct and indirect effects in past and future climate change
Authors: Levy Hiram , Horowitz Larry W. , Schwarzkopf M. Daniel , Ming Yi , Golaz Jean‐Christophe , Naik Vaishali , Ramaswamy V. 
Published: April 2013

AbstractUsing the Geophysical Fluid Dynamics Laboratory's (GFDL's) fully coupled chemistry‐climate (ocean/atmosphere/land/sea ice) model (CM3) with an explicit physical representation of aerosol indirect effects (cloud‐water droplet activation), we find that the dramatic emission reductions (35%–80%) in anthropogenic aerosols and their precursors projected by Representative Concentration Pathway (RCP) 4.5 result in ~1 °C of additional warming and ~0.1 mm day−1of additional precipitation, both globally averaged, by the end of the 21st century. The impact of these reductions in aerosol emissions on simulated global mean surface temperature and precipitation becomes apparent by mid‐21st century. Furthermore, we find that the aerosol emission reductions cause precipitation to increase in East and South Asia by ~1.0 mm day−1through the second half of the 21st century. Both the temperature and the precipitation responses simulated by CM3 are significantly stronger than the responses previously simulated by our earlier climate model (CM2.1) that only considered direct radiative forcing by aerosols. We conclude that the indirect effects of sulfate aerosol greatly enhance the impacts of aerosols on surface temperature in CM3; both direct and indirect effects from sulfate aerosols dominate the strong precipitation response, possibly with a small contribution from carbonaceous aerosols. Just as we found with the previous GFDL model, CM3 produces surface warming patterns that are uncorrelated with the spatial distribution of 21st century changes in aerosol loading. However, the largest precipitation increases in CM3 are colocated with the region of greatest aerosol decrease, in and downwind of Asia.
A high‐frequency response relaxed eddy accumulation flux measurement system for sampling short‐lived biogenic volatile organic compounds
Authors: Arnts Robert R. , Mowry Fred L. , Hampton Gary A. 
Published: April 2013

AbstractA second‐generation relaxed eddy accumulation system was built and tested with the capability to measure vertical biogenic volatile organic compound (VOC) fluxes at levels as low as 10 µg C m−2 hr−1. The system features a continuous, integrated gas‐phase ozone removal procedure to allow for the measurement of highly reactive species such as β‐caryophyllene and polar terpenoids such as linalool. A two‐component internal standard continuously added to the accumulators was used to correct for switching‐induced volumetric errors and as a check on VOC losses exceeding accumulator tube adsorption limits. In addition, the internal standards were used to demonstrate that accumulators quickly return to target flow rates at segregation valve switching frequencies up to at least 0.8 Hz. The system was able to measure daytime hourly fluxes of individual biogenic VOC including oxygenated terpenoids, monoterpenes, and sesquiterpenes.
A new statistical approach to downscale wind speed distributions at a site in northern Europe
Authors: Devis Annemarie , van Lipzig Nicole P. M. , Demuzere Matthias 
Published: April 2013

AbstractThis paper explores a statistical regression approach to downscale large‐scale global circulation model output to the wind speed distribution at the hub‐height of tall wind turbines. The methodology is developed for Cabauw, using observational, ERA‐Interim and ECHAM5 data. The regression analysis is based on the parameters of the probability distribution functions (pdfs) and includes a variable evaluation prior to the development of the statistical models. During winter ECHAM5 performs very well in representing the ERA‐Interim wind speed pdf at hub‐height. However, during summer, the hub‐height wind speed pdf is not well represented by ECHAM5. A regression analysis shows that during summer‐day the hub‐height wind speed is strongly linked to the wind speed at higher, skillfully represented levels. The summer‐day hub‐height wind speed can therefore be skillfully predicted using wind speed pdf parameters of higher levels (R2 of the model using 500 m wind speed scale parameter as a predictor is 0.84). During the summer‐night, the stable boundary layer is much shallower and the statistical model shows that solely the higher level wind speed is not able to skillfully predict the hub‐height wind speed pdf (R2 of 0.59). Including temperature information in the downscaling model substantially improves the prediction of the summer‐night hub‐height wind speed pdf (R2 adjusted of 0.68).
Models versus radiosondes in the free atmosphere: A new detection and attribution analysis of temperature
Authors: Lott F. C. , Stott P. A. , Mitchell D. M. , Christidis N. , Gillett N. P. , Haimberger L. , Perlwitz J. , Thorne P. W. 
Published: April 2013

AbstractThis analysis revisits detection and attribution of free atmosphere temperatures from radiosondes, almost a decade after previous studies. Since that time, data sets have not only become longer, but understanding of observational uncertainty has vastly improved. In addition, a coordinated set of experiments exploring the effects of human and natural forcings on past climate change has been made with a new generation of climate models. These advances allow a much more thorough analysis of the effects of modeling and observational uncertainty on attribution results than previously possible. Observational uncertainty is explored using multiple radiosonde reconstructions including those with ensembles of realizations exploring the effects of processing choices. Modeling uncertainty is explored by calculating multiple fingerprints of natural influence (from changes in solar irradiance and volcanic aerosols) and of human influence (due to greenhouse gases and due to the effects of combined anthropogenic forcings including stratospheric ozone depletion). With increased confidence over previous studies, human influences (both greenhouse gas and other anthropogenic forcings) have been detected in spatiotemporal changes in free atmosphere temperature from 1961 to 2010, irrespective of whether the full atmospheric column (30–850 hPa) is examined or purely the troposphere, with stratospheric ozone depletion dominating the cooling that has been observed in the lower stratosphere. Thus the advances of the last decade yield increased confidence that anthropogenic influences have made a substantial contribution to the evolution of free atmosphere temperatures.