Abstract:In this paper,RAMS(Regional Atmospheric Modeling System) model,coupled with two non-inductive charging parameterization schemes(Saunders and Takahashi schemes),is adopted to stimulate a thunderstorm occurred in Chongqing.A comparative analysis of two schemes is presented on the distribution of hydrometeor particles,the charge density and the distribution of charge structure in the thunderstorm when the charges start to separate and the thunderstorm reaches its maturity.Simulation results show that a dipole characteristic is presented from electrifying to discharging in the charge structure with Saunders scheme,while the characteristic in the charge structure switches from inverse dipole to positive dipole with Takahashi scheme.To study the impact of CCN(cloud condensation nuclei) on the thunderstorm,two sets of sensitivity tests have been carried out.As the initial number concentration of cloud droplets increase,no polarity conversion occurs in the charge structure,however,in the thunderstorm,the charge amount increases and the distribution area of charge expands,which is conductive to the occurrence of lightning.With Saunders scheme,the amount of charge decreases when the initial number concentration of cloud droplets is over 2 000 cm^-3.Through analysis of the microphysical field and microphysical process,it is found that the mass mixing ratio of ice-phase particles increases as the initial number concentration of cloud droplets increases,while the mass mixing ratio of graupel particles decreases when the initial number concentration of cloud droplets is over 2 000 cm^-3,with Saunders scheme.This verifies the impact of CCN variation on the microphysical process,thus further on the distribution of charge in the thuderstorm and the occurrence of lightning,especially the impact of variation of ice-phase materials on the electrification process of thuderstorm.

Abstract:The regional climate model RegCM4.0 coupled with land surface and simple chemistry/aerosol module is used to simulate the spatial-temporal distributions and direct effect on climate of carbon aerosols over Asian area from 2000 to 2008.Results show that carbon aerosols are mostly concentrated in Indian peninsula and middle-eastern China in winter and summer,with maximum values in northeastern Indian peninsula and Sichuan Basin of China.With the outbreak of Asian summer monsoon and the arrival of the rainy season,the loading(distribution) of carbon aerosols significantly decreases(moves northward) in summer comparing to those in winter.In winter,the surface temperature is decreased by carbon aerosols over Asian area.In summer,the surface temperature is increased in Sichuan Basin,North China and South China,which is caused by the “semi-direct effect” of black carbon.There are significant differences in precipitation change caused by carbon aerosols among the different areas.Carbon aerosols also can strengthen South Asian summer monsoon.There are big differences in the climate responses to carbon aerosols between East Asia and South Asia.In summer,the low level air temperature is decreased and the middle-upper level air temperature is increased in South Asia,but warming mainly appears in the lower level in East Asia.

Abstract:This paper studies the high-temporal-resolution properties of atmospheric extinction,especially aerosol extinction,with the hourly data of relevant factors(including total atmospheric extinction coefficient,absorption coefficient of gas molecule,absorption and scattering coefficients of aerosol,and inhalable particle number concentration) for the year of 2010 in Shenyang area.Results show that the total extinction and aerosol scattering coefficients both show a single cycle pattern with a peak in 05:00—06:00 BST and a valley at 15:00 BST in one day.The total extinction coefficient is the highest in snowy days,then in hazy days,and it is the lowest in sunny days.The correlation coefficient between the aerosol extinction coefficient and the particle number concentration increases with the decreasing of particle size.

Abstract:The effects of aerosols on cloud macro-physical,microphysical and radiative properties at typical sites are analyzed using the objective cloud observations from CloudSat and the passive aerosol retrievals from MODIS(Moderate-Resolution Imaging Spectroradiometer).Results show that aerosols have significant impact on cloud over both continental and marine sites.With the increase of aerosol optical depth(AOD),the low(high) level cloud fraction at sites with relative weak water vapor conditions shows decrease(increase) trend,while the cloud fraction of all altitudes increases at sites with relative strong water vapor conditions.With the increase of AOD,occurrence probabilities of cloud layers with high(low) cloud top height at each site show an increase(a decrease) trend.With the increase of AOD,the effective radius of cloud droplet and ice crystal decrease,both the shortwave and longwave cloud radiative forcings at atmosphere top are enhanced,the increase of absolute value of shortwave cloud radiative forcing is large,and the increase of longwave cloud radiative forcing is relatively larger at all sites.The variations of meteorological elements under large(small) AOD conditions indicate that the significant changes of cloud physical and radiative properties with AOD can not be explained by large scale dynamical influence.

Abstract:Total 109 precipitation samples were collected in north suburb of Nanjing from March to June 2011.In order to investigate the chemistry characteristics of precipitation,the concentration of water-soluble ions were analyzed and the air mass sources of precipitation were also discussed using the back trajectory model.Results show that the precipitation is mainly controlled by southern and northern air masses,and the concentrations of major ions from precipitation of northern air masses are higher than those from southern.The sea salt tracer method and the correlation analysis indicate that NO₃^- and SO₄^2- are mainly from coal burning,industrial emissions and vehicle exhaust emissions.Ca²⁺ and Cl^- mainly derive from crustal and marine sources,respectively.K⁺ and Mg²⁺ are both from marine and terrestrial sources,while the terrestrial contribution of Mg²⁺ is dominant,and the impact of marine on K⁺ is lower than on Mg²⁺.Due to the scavenging process,the concentrations of different ions and the enrichment factors of main ions in the early period of precipitation are higher than those in the whole period of precipitation,which are attributed to the main contribution of local pollution sources.

Abstract:In order to make a study of the kinematic and dynamic characteristics of convective cells,Doppler radar reflectivity factor data and radial velocity data are used to conduct radar echo extrapolation in this study.Therefore,the horizontal wind fields of eight different heights are retrieved by VAD(Velocity Azimuth Display) method and TREC(Tracking Radar Echoes by Correlation) method,which are taken as the motion vectors of echoes to get the extrapolated forecast of CAPPI(Constant Altitude Plan Position Indicating) reflectivity factor there.According to the methods of VAD and TREC,the radar echo extrapolation of two rainstorm processes have been carried out.The results indicate that the location of radar echoes during the next 60 min forecasted by the two methods coincides well with that from the observations.The extrapolation results of VAD and TREC are similar at some altitudes,and correspond well at the levels with the best results.The two extrapolation experiments show that the height levels with the best forecast results are related to the weather process,especially the vertical distribution of horizontal wind in the precipitation echo,which are not just limitted to 2.5—3.0 km.

Abstract:In stratiform precipitation,if an appropriate correction is not applied,the bright band(BB) that is induced by melting affection will cause significant overestimation in radar quantitative precipitation estimation(QPE).Therefore,the main objective of the current study is to develop an algorithm that is based on weather radar vertical profile of reflectivity(VPR) data and can automatically correct large errors caused by BB effects.Therefore,it will improve a real-time weather radar derived QPE.Firstly,we divide radar echoes into convective and stratiform before a VPR correction is applied.In this study,in addition to the method of SHY95,we make use of a full three-dimensional volume of reflectivity characters to avoid errors caused by BB in heavy stratiform rain.Then,the stratiform area is further divided into two parts:one is the BB affected area while the other one is not.The VPR are only derived and applied to the bright band affected area(BBA) rather than to the whole radar coverage.The BB boundaries are identified by a new algorithm which utilizes a rotational coordinate system for identifying the upper and lower boundaries of BB.Finally,the slope over and under BB is obtained by a least squares linear fitting to the VPR between the BB boundaries in order to smooth the incorrect VPR curve.The correction method was tested by ten events in different seasons in Beijing from 2010 to 2011.It is found that after the correction of BB,the RMSE,RMAE and RMB of radar-gauge pairs reduce significantly (1.538 mm,0.41 and 0.468 on average,respectively).So we can reach the conclusion that the correction is effective in reducing overestimation errors in radar derived QPE.

Abstract:In order to study the effect of cloud saturation on thunderstorm electrification,a parameterization of non-inductive graupel-ice charge separation S91 based on the laboratory results of Saunders et al.(1991) is introduced into a three-dimensional dynamic-electrification coupled model.The effective liquid water content and environment temperature in S91 are replaced by cloud saturation,resulting in the deformation of S91.The evolution characteristics of non-inductive charge separation polarity,magnitude,charge structure and their relationship with ice crystal and graupel particle distributions produced by the deformation of S91 and original S91 in a typical storm before the first discharge are analyzed,respectively.The results indicate that the transfer charges per collision and the change rates of charge density adopted in these two parameters are the same,but difference of factors which determine the increase of graupel and ice particles in these schemes exerts a relatively important influence on the distribution of charge.In the deformation of S91 scheme,the domain polarity of non-inductive charge separation changes is basically positive,the charge structure switches from unipolar to tripole,and it tends to produce a positive dipole charge structure.In addition,the difference of charge distribution and charge separation changes in the schemes are caused by the difference of coincidence region between graupel and ice particles.

Abstract:The COSMIC retrieved temperature and relative humidity profiles are compared with the collocated spatially and temporally ECMWF(European Centre for Medium-Range Weather Forecasts) and NCEP(National Centers for Environmental Prediction) model objective analysis fields as well as radiosonde observations on global scale in different seasons in 2009.The primary research results show that the distributions of the deviations and the standard deviations from these data sources are similar in summer and winter,independent of seasons.The vertical and horizontal temperature distributions of these data sources are very close.Either temperature or relative humidity profiles from ECMWF are more close to COSMIC retrievals than NCEP fields.The humidity profiles of model objective analysis are all higher than radiosonde observations in nearly whole troposphere and wetter than COSMIC retrievals in middle-upper troposphere over most ocean area.The COSMIC retrieved relative humidity profiles are higher than the radisonde measurements,having obvious positive deviations with maximum(about 30%) at 300 hPa.

Abstract:The precipitation process of a wintertime cold front in the Taiwan Strait was simulated based on the mesoscale model WRF,combined with FY-2E satellite image and the conventional observation data.Conclusions are as follows:1)The microphysics scheme is sensitive to the simulation of winter cold front in the Taiwan Strait,and Milbrandt double-moment microphysical scheme can successfully reproduce the hierarchy of cloud system,the ice-phase precipitation process and the convective development of clouds,which is more superior than other microphysical schemes for the simulations of 24 hours accumulated precipitation.2)The mixing ratio of precipitation particles(rain,snow and graupel) of frontal zone is larger than that of the post-frontal part.The rain band of frontal zone gathers in the middle of surface frontal line,and the post-frontal rain band is deflected to the southwest cold region.3)The near frontal zone clouds are influenced by the low-level jet stream and the orographic uplift in the middle of Taiwan Island,therefore it results in a strong precipitation center generating in the windward slope,which corresponds to the high content area of graupel in the air.4)High equivalent potential temperature,strong convergence,positive vorticity and convective instability at the lower level accompanied by strong divergence and negative vorticity at the higher level is the major reason for the maintenance and development of the cold frontal clouds.

Abstract:According to the framework of energy cycle proposed by Lorenz in 1967,the atmospheric energy cycle is estimated on a monthly basis in the Northern Hemisphere using the NCEP/NCAR reanalysis daily data for the period of 1958—2011.The annual variations of energy reservoirs,conversions,exchanges across the equator,generations and dissipations have been investigated in the present paper.The results show that the energy cycle of the Northern Hemispheric atmosphere varies on annual time-scale evidently.Reservoirs and conversion rates change in the same phase,with values larger in winter,smaller in summer.In winter,the zonal mean energies and eddy kinetic energy are transported northward from the Southern Hemisphere into the Northern Hemisphere.However,in boreal summer,they are transported southward from the Northern Hemisphere into the Southern Hemisphere,whereas the exchange of eddy available potential energy at the equatorial boundary is in contrast.A maximum in generation of the zonal mean available potential energy takes place in the fall,and the generation of eddy available potential energy has a maximum in the summer.The dissipations of both zonal mean and eddy kinetic energy are stronger in winter but weaker in summer.In the annual mean case,the cross-equatorial fluxes are smaller than the energy conversion processes.In the meridional direction,the zonal mean available potential energy mainly appears in high-latitudes,the zonal mean kinetic energy mainly in mid-and low-latitudes,and the eddy energies mainly in mid-and high-latitudes.Further more,the conversion processes of atmospheric energies are more active in the middle latitude regions.

Abstract:Based on the NCEP/NCAR daily reanalysis data during 1954—2010 and the daily precipitation data at 753 stations in China,the beginning and end dates of rainy season over North China are defined.Analysis shows that there are two kinds of precipitation processes,one is unimodal precipitation process,the other is bimodal precipitation process.Meanwhile,the paper selects the two kinds of typical precipitation processes and studies their characteristics and mechanisms.Results show that:1)During the rainy season of North China,the ridge of subtropical high are not interrupted during the unimodal precipitation process,but there is precipitation break phenomenon during the bimodal precipitation process,which is caused by the eastward retreat and southward downshift of subtropical high.2)In the unimodal precipitation years,the phenomenon of monsoon break is not obvious and the influence of monsoon can continue to the end of the rainy season.However,in the bimodal precipitation years,the strengthening(weakening) of monsoon corresponds to the peak(break) of precipitation.3)Temporal variation of the filtered precipitation in North China shows that a precipitation peak will occur when there is a good corresponding relation between the peaks of 30—60 d and 7—14 d oscillations,and a rainfall break will happen when there is a good corresponding relation between the trough of 30—60 d oscillation and the peak of 7—14 d oscillation.4)The evolution of bimodal precipitation in North China obviously has a close relation to the low frequency oscillation of zonal wind in summer.

Abstract:To strengthen the application of satellite data in assimilation system,this paper constructed the WRF-EnSRF satellite data assimilation system with RTTOV radiative transfer model as the observation operator,and sat up some modules including satellite data reading,bias correction and quality control,thereby achieving the autonomy of the WRF-EnSRF satellite data assimilation system.With the assimilation system,the assimilation numerical simulation experiment of assimilating NOAA-16 AMSU-A and AMSU-B radiance data is conducted with a heavy rainfall occurred in South China.Test results show that,with bias correction,the deviation between observed and simulated brightness temperatures is reduced.For this experiment,the major effect is reflected in the improvement of amount of precipitation forecast result.For TS score,precipitation in the assimilation experiment is better than that in the control experiment at torrential rain level.Thus,it further proves the validity of the satellite data assimilation system.

Abstract:Based on the conventional observation data,Doppler radar observation data,wind profiler radar data and NCEP/NCAR reanalysis data,a squall line event occurred in Guangzhou Baiyun airport terminal area on 30 April 2013 was analyzed and simulated.Results show that the weather event is caused by the east movement of the upper trough,which drives weak surface cold air southward.The shape and intensity changes of squall line simulated by WRF(Weather Research and Forecasting) model are quite in agreement with the observations.There are obvious tilted updraft in the squall line.In the stage of development,there are updraft in the whole squall line,while in the mature stage,the updraft above 600 hPa and the downdraft in middle and low levels as a result of drag effect of heavy rain.There are obvious surface cold pool and thunderstorm high during the squall line process,and there is an obvious correlation between intensity change of squall line and change of cold pool.In the stage of development,the thunderstorm high locates in the low and back parts of the whole squall line,while in the mature stage,the positive pressure change in the low part and the negative pressure change in the back part are symmetrical.

Abstract:There is a north-south reverse pattern in precipitation in flood season(May to September) over the Tibetan Plateau.Based on the monthly rainfall data of 67 stations over the plateau from 1967 to 2008,this paper studies the principal spatial patterns of monthly rainfall during the flood season,and the moisture configurations and circulation anomalies in the early summer(May to June) and midsummer(July to August),respectively.It is found that there are two main patterns in summer,but they are different between the early summer and midsummer.The former has an advantage in north-south reverse type(NSRT),while the latter exceeds in whole region consistent type(WRCT).When the rainfall shows NSRT,the moisture transport comes from south to north Tibetan Plateau in the early summer,and the convergence(divergence) of water vapor locates in north(south) Tibetan Plateau in the midsummer.While the rainfall shows WRCT,the moisture transport comes from western Pacific in the early summer.In the midsummer,it comes from the eastward ransport of water vapor from Arabian Sea,which enters the plateau from its southwest areas.At 500 hPa,the meridional(zonal) geopotential height differences between the two patterns are predominant in the early summer(midsummer),and the circulation systems impacting distributions of precipitation anomalies are mostly deep.

Abstract:Based on the PM₁₀,PM_2.5,SO₂,NO₂ and O₃ concentration data from the Xuyi county environmental monitoring station and the meteorological data from Xuyi station meteorological data from January to December of 2014,the air quality change under different meteorological conditions in Xuyi County is analyzed.The results show that the main pollutants in Xuyi county is PM_2.5 and PM₁₀while SO₂ and NO₂ pollution is light.Air pollution is more serious in spring and winter while it is not so severe in summer and autumn.Precipitation can improve air quality and remove air pollutants obviously.The air quality is better when the temperature is higher than 30 ℃ or lower than 0 ℃ while it is worse when the temperature is between 0 ℃ and 20 ℃.Moreover,the air quality is worse when the wind comes from east while it gets better when the wind comes from north.