Abstract:Based on the forecast dataset of 500 hPa geopotential height fields from NCEP ensemble prediction system(EPS) and the corresponding NCEP/NCAR reanalysis dataset,the ensemble forecasting performance in Eurasia region(EA) is compared with the performance in North America region(NA).By several forecast verification and evaluation methods,the comparisons focus on the ensemble mean forecasts and ensemble probabilistic forecasts.In general,the NCEP-EPS circulation ensemble performance in EA is nothing less than the prediction in NA.1)ACC shows that,except in winter,the ensemble mean forecasts in EA in the other three seasons are clearly superior to those in NA,and their difference of maximal lead time of useable forecasts is 0.6-1 d,with the largest difference in summer.RMSE shows that the forecast results in EA in the four seasons are better than those in NA.2)The seasonal differences of reliability of ensemble probability forecasting are not evident.For the shorter(longer) lead time,the reliability in NA(EA) is better.The identification range of synoptic events in EA is relatively smaller,but the reliability is relatively higher in the region.This conclusion is opposite in NA.3)In summer,the ensemble probability predictions in EA are clearly superior to those in NA.In autumn and winter,there are better results in NA.In spring,when the lead time is less than 5 d,the results in NA are better,but when it is more than 5 d,there is better forecasting resolution in EA.

Abstract:Based on the daily precipitation data of six representative stations in China from May to September,the joint probability characteristics of the heavy precipitation and the corresponding course precipitation are investigated by the bivariate Gumbel-Logistic model.Results show that the bivariate Gumbel-Logistic model is suitable for the joint distribution of the heavy precipitation and the corresponding course precipitation at the selected stations.The probability of the joint distribution is smaller than the probability of either.On the certain heavy precipitation condition,the more the course precipitation is,the longer the return period is.The return period of the corresponding course precipitation can be prolonged by the increased amount of heavy precipitation.The probability of course precipitation in south is larger than that in north and the same as the amount of course precipitation under the same heavy precipitation conditioan.The study is a new attempt of research on extreme precipitation in all domains and reveals the multi-sided probability characteristics of extreme climate events.

Abstract:Using the data of DEM with scale of 1:250 000 and routine meteorological observations,this paper achieves the distributed simulation of global solar radiation(GSR) of Jiangsu Province.Spatial distribution maps of normals of monthly and annual GSR with the resolution of 100 m×100 m of Jiangsu Province are generated and their spatio-temporal distribution characteristics are analyzed.The results are as follows:1)The normals of annual GSR in Jiangsu Province is 4 749 MJ/m²;2)The annual GSR has a progressive increasing trend from southwest to northeast,i.e.Lianyungang has the highest value of 5 063 MJ/m² and Wuxi the lowest value of 4 514 MJ/m²;3)GSR in Jiangsu Province reaches the highest in May and the lowest in December.The statistics of sunshine hours observations,i.e.annual sunshine hours,annual days with daily sunshine hours≥6 h and the ratio of the maximum to the minimum of monthly days with daily sunshine hours≥6 h,are used to analyze the stability of solar radiation resource in Jiangsu.Its pattern also has a southwest to northeast change trend,which is to say that the northeast region of Jiangsu has the highest predominance in solar energy utilizing.

Abstract:Using ground-observed albedos from four stations over the Tibetan Plateau from 2002 to 2004 in the CAMP/Tibet experiments,the accuracies of Terra MODIS(MODerate-resolution Imaging Spectroradiometer) shortwave bands(0.3-5.0 μm) albedos in 1 km resolution derived with the full inversion and the magnitude inversion are individually quantitatively assessed.When MODIS albedos are derived with the full inversion,the root-mean-square errors(RMSEs) between the ground-observed albedos and the black-sky albedos(BSA),and the white-sky albedos(WSA) are 0.018 7 and 0.016 8,respectively;when MODIS albedos are derived with the magnitude inversion,they are 0.076 6 and 0.076 1,respectively.And,when MODIS albedos derived with the full inversion and the magnitude inversion are all included,the RMSEs are 0.067 9 and 0.067 5,respectively.When the ground-observed albedos and MODIS albedos derived with the magnitude inversion are both from the no-snow condition,RMSEs between the ground-observed albedos and BSA,and WSA derived with the magnitude inversion are 0.035 2 and 0.036 4,respectively.However,when the ground-observed albedos are from the snowy condition,while MODIS albedos derived with the magnitude inversion are from the no-snow condition,RMSEs between the ground-observed albedos and BSA,and WSA derived with the magnitude inversion are 0.155 6 and 0.154 1.

Abstract:The fog comprehensive observation data collected in the surface layer in northern suburb of Nanjing (32°12'N,118°42'E,25 m a.s.l.) in winter from 2006 to 2009 are used to investigate the interaction between radiation characteristics and fog microphysical structure.Results show that,when the net radiant flux density lies between -50 and +25 W·m^-2,the fog droplet number concentration increases gradually and the fog droplet number density increases more significantly with the decrease of fog droplet size.It indicates that the surface radiation cooling or very weak heating can facilitate the activation and condensational growth of fog droplets.While the net radiant flux density is greater than +25 W·m^-2,the fog droplet number concentration declines significantly and the fog droplet number density reduces more rapidly with the decrease of droplet size.The solar shortwave reflectivity is strongly influenced by the fog droplet number concentration,mean radius,and liquid water content.During the fog events,while the fog droplet number concentration and liquid water content increased by 100 cm^-3 and 0.001 g·m^-3,the solar shortwave reflectivity would increase by 5.29×10^-3 and 1.18×10^-4,respectively.

Abstract:The transport process of pollution gases under different weather situation are simulated at Mountain Huang on 26 April and 2 May 2008 by using a new generation atmospheric chemistry transfer model WRF-Chem.Results show that,in sunny conditions,the pollution gases are transported vertically from downhill to uphill by mountain-valley breeze circulation,the transport of pollutants in the surrounding areas has less effect on the volume fraction of pollutants at Guangmingding,and new particle formation is the main source of atmospheric aerosols.However,in cloudy conditions,the pollution gases are transported vertically to the uphill by turbulent diffusion in boundary layer,the short range transport has much effect on the volume fraction of pollutants at Guangmingding in the nighttime,and the aerosol particles mainly come from the ground transport.

Abstract:Measurements of atmospheric aerosol scattering coefficient(ASC) over the northern suburbs of Nanjin from 2009 to 2010 are carried out by the Integrating Nephelometer.Analysis results show that ASC has obvious seasonal variations with the lowest in spring,the highest in fall,and little difference between summer and winter.The ASC ranges from 51.6 Mm^-1 to 2 748.3 Mm^-1 with the average of 478.6 Mm^-1 in different seasons.The diurnal variation of ASC shows a bimodal distribution.The ASC has a positive correlation with air relative humidity.It also has a close correlation with surface wind direction, and it is the highest when the wind is blowing easterly,followed by the southerly and westerly wind.Aerosol can be significantly removed by precipitation.There is a negative correlation between the visibility and ASC when the visibility higher than 5 km.The ASC shows the biggest positive correlation with SO₂(0.68) in autumn and NO₂(0.62) in spring which is significant at the 95% confidence level.

Abstract:To understand the chemical composition and temporal variations of atmospheric precipitation to the north of the Yangtze River in Nanjing,48 precipitation samples were collected and analyzed from March 2007 to September 2008.In the precipitation samples,44.5% in 2007 and 59.3% in 2008 were acidic.Compared with the data of 2005 and 2006,the acidity and acid rain frequency increased significantly;the mass concentration of NO₃^- had a slight increase and the mass concentration of NH₄⁺ had a relatively obvious increase.The dominant atmospheric pollutant in this industrial area was SO₂,mainly coming form coal burning and car exhaust.Comparison analysis showed that in recent years,the SO₄^2-'s contribution to precipitation acidity reduced while that of NO₃^-'s enhanced markedly.

Abstract:Using the NCEP/NCAR monthly mean reanalysis data from 1980 to 2009,this paper investigates the weakening trends of enstrophy in troposphere of Northern Hemisphere under background of global warming.Results show that the enstrophy has a weakening trend in the Northern Hemisphere from 1980 to 2009,especially in the North Pacific and polar regions.The zone of 12.5-50°N is the key area of enstrophy change in the Northen Hemiphere.Changes of the subtropical westerly jet in association with the meridional gradient of air temperature show that the jet intensity has a weakening trend,which is in accordance with the enstrophy change.A vector E is employed to diagnose the Rossby wave propagations in the atmosphere,showing that the disturbances in the atmosphere elongate more meridional in the Northern Hemisphere except western Europe.The meridional eddy heat fluxes in the Northen Hemiphere have also been weakening in the past 30 years.These results are helpful for our better understanding the circulation changes and the influences of global warning.

Abstract:The CCSM3(Community Climate System Model version 3) developed by US National Center for Atmospheric Research is used to study the characteristics of thermohaline circulation(THC) in the freshwater disturbance experiments with different mean THC intensities,and the influences of THC on the climate in North Atlantic.Results show that:1)In different THC average intensities,the climatology of marine,atmospheric elements over North Atlantic are significantly different.Compared to the high average intensity,in the low average intensity,SST(sea surface temperature),SSS(sea surface salinity),SSD(sea surface density),SAT(surface air temperature) over North Atlantic are weakened,and the largest negative anomaly locates in GIN(Greenland sea-Iceland sea-Norwegian sea).With the elevation of SLP(sea level pressure) and the cooling of SST and SAT,there is an abnormal cold high pressure over North Atlantic.Sea ice distribution area expands southward.The precipitation in the western tropical Atlantic decreases,leading to ITCZ(intertropical convergence zone) moving southward.2)In different THC average intensities,the most notable areas of interannual SST,SSS and SSD anomalies are different.The most significant area locates in GIN in the high average intensity,while in the Labrador waters in the low average intensity.3)In the high average intensity,the maximum of dominant variability mode of SST over North Atlantic locates in GIN,while it does not exit in GIN in the low average intensity.The dominant variability mode of SLP over North Atlantic is NAO-like mode,but the NAO-like mode is more significant in high average intensity.

Abstract:The effectiveness of the EnSRF(ensemble square root filter) data assimilation system in assimilating Doppler radar data on convective scales is investigated for cases whose behaviors span supercellular,linear,and multicellular organizations.The impacts of potential temperature and water vapor at different levels on ensemble spread and assimilation effect during initial perturbations are also investigated.The EnSRF performs effectively and produces results of comparable quality for each of the cases.The root mean square innovations of radial velocity and reflectivity decrease to 3-5 m/s and about 10 dBz respectively after roughly 24 min of assimilation and maintain the values throughout to the end of the 60 min period of assimilation.The ensemble spread and assimilation effect are sensitive to the magnitude of perturbation in thermal field,which implies that larger ensemble spread and better radial velocity analysis can be obtained by increasing the standard deviation of potential temperature and water vapor mix ratio appropriately during initial perturbation.

Abstract:A four-dimensional variational Doppler radar analysis system (VDRAS) is used to analyze the three dimensional wind fields and microphysical fields of a rainstorm case in Beijing on July 30,2008.After discussing some key points in short-term and nowcasting forecast such as the weakening and dissipation of the eastern echo as well as heavy rain area and the turning of echo,some preliminary conclusions were obtained:1) 12-24 minutes before the weakening and dissipation of the eastern echo,a hollow structure (even negative point) appeared in corresponding analyzed perturbation temperature positive region at the height of 4.7 km,and at the same time ascending and descending flow separated in the same region at the height of 1.7 km.2) If the duration of the analyzed perturbation temperature in some regions was higher than that in other regions for 2 hours or longer,or the perturbation temperature increased rapidly in few minutes and reached the extreme value (above 2℃),there was a good chance that heavy rain would occur in 1-2 hours in this region.3) The turning of the echo was conducted by the western air flow of anticyclone style circulation flow at the height of 1.7 km.A convergence ascending flow was horizontally transported from western region to Miyun and Pinggu in the eastern region,and then a divergence descending flow of anticyclone type came into being.The moving of radar echo was affected by the air flow and this flow occurred about 1 hour before the echo turning.

Abstract:The Mesoscale Convective Systems(MCS) in the coastal areas of South China during 16th-17th July 2006 was simulated using mesoscale numerical model WRF(weather research and forecasting model),and we analyzed the precipitation process combining with observation data.The results show that:1)The activity of MCS was closely related to the remnant of the downgraded severe tropical storm "Bilis" and southwest monsoon.The tropical depression provided dynamic conditions for MCS and southwest monsoon brought plenty of aqueous vapor to South China,the continued combination of tropical depression and southwest monsoon caused the formation and development of MCS;2) The MCS has an obvious asymmetry structure,the upper cloud stretched to south and the nephsystem distributed in a northeast-southwest band and mainly located in the south of tropical depression;3) Using WRF model to simulate the heavy rain process produced good results,which represented the development of MCS and the distribution of rain band;4) The cloud water content was little and ice crystal content was large in the mesoscale convictive cloud cluster,so ice crystal precipitation mechanism was the main precipitation mechanism.

Abstract:The NCEP GFS reanalysis data(resolution of 0.5°×0.5°) and surface observation and Doppler radar data were used to analyze the mesoscale systems of the torrential rain which occurred over the Jianghan Plain in Hubei on 18 June.Results show that the torrential rain was mainly caused by the deep low vortex over the Jianghan Plain,the dry line in the middle troposphere-boundary layer and mesoscale low pressure on surface were the main trigger mechanism,and the southwest jet offered sufficient vapor for the rain.After studying the radar echoes feature,it is found that the rain intensity was in good consistency with the vertical thickness of radar reflectivity factor above 45 dBz under 0℃ level and with the vertical integrated liquid value.

Abstract:Change of the first frost date has obvious effect on agricultural distribution and farming pattern.Based on each year's first frost date data and each day's minimum ground temperature data from 62 meteorological stations in Shanxi Province from 1961 to 2010,the first frost date climate change characteristics and its periodicity in Shanxi Province are analyzed with statistical method.The results show that:1) The average first frost date in Shanxi Province has a delaying trend and changes with decades.It was advanced visibly in the seventies and the nineties of the twentieth century and was delayed obviously in the sixties and the eighties of the twentieth century and in this century.2) The spatial distribution of the first frost dates in Shanxi Province appears from the north to the south in five steps;it appears from the second ten days of September in the north to the first ten days of November in the south.3) The average first frost date in Shanxi Province had a mutation in 1989.4) The first frost date in most areas has a delaying trend,with exception only in some areas such as the south and middle south parts.5) The Morlet analysis results show that cycles of the first frost frequency,the mild first frost frequency,the moderate first frost frequency and the severe first frost frequency are 5 a,2 a,5 a,6 a respectively.Now,Shanxi is in the phase when the first frost and the mild first frosts are delaying while the moderate and severe first frosts are advancing.

Abstract:Using one year ground atmospheric electric filed data by the AMEO340 installed in Nanjing University of Information Science and Technology,this paper calculates the ground atmospheric electric field sampling series by the fast Fourier transform in order to get power spectrum of the ground atmospheric electric field series.The ground atmospheric electric field data of sunny and lightning days are analyzed with seven-layer decomposition of the sym5 wavelet function,which decreases the overlapping degree of ground atmosphere electric field data waveform to some extent.The ground atmospheric electric field signals of lightning days are decomposed by the seven-layer decomposition.The low-frequency component of the ground atmospheric electric field signals not only can highlight its main change trend,but also can clearly identify the number of strong positive and negative ground flashes.So it can supply more effective information for the lightning nowcasting by using the characteristics of the ground atmospheric electric field singnals.