Abstract:On basis of the back propagation artificial neural networks(BP ANN) method,and under consideration of the mean value differences caused by different sample collections for their individual differences and interdecadal variations,which may influence the simulation and prediction of summer rainfall patterns over eastern China,the cross validation and ensemble prediction ideas are adopted to improve the prediction method.An independent prediction is gotten during each cross validation test,and then many times cross validation test by the ANN model established based on different sample collections may give many times prediction results for the predicted year.Its performance seems good in the prediction test of four rainfall patterns over eastern China in summer.

Abstract:A new concept of thermodynamic shear advection parameter is introduced in this paper.Based on the parameter and the theory of wave-flow interaction,we conducted the diagnostic analysis on the heavy-rainfall event caused by landfall typhoon "Fung-wong".With the assimilation data of the ARPS mode,M and ▽·F were calculated to analyze the relationship between them and the observed 6 h accumulated surface rainfall.The result showed that the abnormal values of wave action density M(disturbance thermodynamic shear advection parameter) always covered the observed precipitation regions and both their horizontal distribution and their temporal evolution were quite similar.The positive high-value area of the parameter corresponded well with the observed 6 h accumulated surface rainfall.The analysis of ▽·F showed that in the process of rainfall which was caused by the landfall typhoon,the potential vorticity disturbance of ageostrophic wind was the main forcing term affecting the variation of disturbance thermodynamic shear advection parameter.Further analysis showed that the major exchange between the disturbance and basic states was the advection exchange of disturbance heat,while the advection exchange of disturbance momentum was very weak.

Abstract:By using GODAS monthly mixed layer depth(MLD) and 160-station monthly precipitation data in China,the seasonal and interannual characteristics of MLD are analyzed over the north Pacific,along with the influences of MLD interannual anomaly on summer rainfall in China discussed.The results show that:1) The MLD is the deepest over the latitudes from 30 to 40°N and is larger in winter and spring than in summer and autumn.2) The interannual anomaly is most prominent over the middle part of the north Pacific near the international date line in four seasons;but only the MLD anomaly is somewhat related to ENSO in summer,and MLD is of interdecadal anomaly characteristics in autumn,winter and spring.3)When MLD increases over western and middle part of the north and central area of Pacific in the previous winter,the precipitation may decrease over the part of the lower Yellow River,Huang-huai,Jiang-huai and to the south of the Yangtze River reaches(except the south of Guangxi) and the precipitation may increase in He-tao,east part of Neimeng and most part of Northeast China in the following year.

Abstract:By using the rainfall and air temperature observation data from 63 surface stations in South China during 1961—2007,the monthly dry and wet states were calculated by climatic dry and wet index,whose results could obviously tell the dry seasons from wet ones in South China.The spatial-temporal characteristics of dry and wet states over South China in recent 50 a were analyzed by trend analysis and EOF synthetical analysis.The trend analyses reflected the fact that for the whole region of South China,the climate from February to March,May and from July to August tended to be wetter,and it became dryer in April and from September to December.There were few changes in January and June.The results showed that the autumn drought was more severe while the spring drought was lighter and the summer flood was more severe in the past 50 a.EOF analysis revealed that the phases of time evolution were contrast to each other in east and west regions of South China.Synthetical analysis showed that dry and wet states were mainly affected by air-sea and air-land interactions.

Abstract:Based on the hourly precipitation observed by automatic weather stations(AWS) in China and retrieved from CMORPH(CPC MORPHing technique) satellite data,the merged precipitation product at hourly/0.1°lat/0.1°lon temporal-spatial resolution in China is developed through the two-step merging algorithm of PDF(probability density function) and OI(optimal interpolation).In this paper,the quality of merged precipitation product is assessed from the points of temporal-spatial characteristics of error,accuracy at different precipitation rates and cumulative times,merging effect at three station network densities and monitoring capability of the heavy rainfall.Results indicate that:1)The merged precipitation product effectively uses the advantages of AWS observations and satellite product of CMORPH,so it is more reasonable both at the precipitation amount and spatial distribution;2)The regional mean bias and root-mean-square error of the merged precipitation product are decreased remarkably,and they have a little change with time;3)The relative bias of merged precipitation product is -1.675%,less than 15% and about 30% for the medium(1.0—2.5 mm/h),medium to large(1.0—8.0 mm/h) and heavy rainfall(≥8.0 mm/h),respectively,and the product quality is improved further with the cumulative time increases.The merged precipitation product can capture the precipitation process very well and have a definite advantage in the quantitatively rainfall monitoring.

Abstract:Based on the conventional observations,NECP/NCAR reanalysis data,automatic weather station intensive observations and Doppler radar data,this paper contrasts the two typical squall line processes in Jiangsu and its surrounding areas on 28 Apirl 2006 and 14 June 2009.Results show that,prior to the two squall line processes,the warm advection obviously occurs in the lower troposphere and the cold advection appears in the middle-upper troposphere,which is helpful for the formation and development of stratification instability.During the movement and development of squall lines,a clear convergence line occurs in the surface wind field,which plays an important role in the triggering and maintenance of the squall lines.There are obvious differences of thermal and dynamic structures between the environment fields of the two processes.For the thermal structures,the former happens in spring when cold air is still strong and warm advection in the lower troposphere is one of main reasons of stratification instability,and the latter happens in summer when warm moist air is active and cold air invasion in middle-upper troposphere deserves attention greatly.The dynamic analysis shows that low level convergence and lifting conditions of the former are better than those of the latter.However,the thermal conditions of the latter are predominant,and it is easier to develop once the convection starts.

Abstract:The gradient and turbulent data observed by 70 m meteorological tower at the north part of Poyang Lake are employed to analyze the characteristics of surface layer of a heavy rain process on 6 June 2011.It is found that,under the weather background of upper trough and southwest jet,the heavy rain process is obviously affected by the complex surface of Poyang Lake.Before the precipitation happens,affected by the warm southeast advection,the water vapor and instability increase.During the heavy rainfall process,the sensible and latent heat fluxes,and the horizontal and vertical turbulent momentum fluxes increase rapidly,and the water vapor transport from Poyang Lake surface strengthens the rainfall.In addition,the turbulent kinetic energy increases rapidly and reaches a peak during the heavy rainfall,while the mean kinetic energy reaches a peak after the heavy rainfall process,showing that the local surface provides a dynamic effect on the heavy rainfall process.Dimensional analysis shows that the mesoscale momentum flux is larger than the turbulent momentum flux before the heavy rainfall,however,during the heavy rainfall process,the turbulent flux increases obviously.

Abstract:In order to simulate meteorological parameters more accurately in the Planetary Boundary Layer(PBL) over complex terrain,the SRTM3 data from NASA was used in WRF model.With configuration of four PBL parameterization schemes(YSU scheme,ACM2 scheme,MYN scheme,and BL scheme) and two geographical data(SRTM3,GTOPO30),meteorological parameters in the PBL of the Mt Huang area during 24—25 April 2008 were evaluated.Temperature and dewpoint temperature of 2 m,wind speed of 10 m and water vapor distribution from simulation were contrasted to the observational data from 19 meteorological stations and 2 sounding stations in the Mt Huang area.Results show that YSU scheme was best for 2 m temperature simulation and ACM2 scheme was best for 2 m dewpoint temperature and 10 m wind speed simulation in the four PBL schemes with both geographical data;when SRTM3 data was used in WRF model,the mean RMSE of 2 m temperature simulated by the four PBL schemes were reduced by 3.79%(YSU scheme),2.48%(ACM2 scheme),3.8%(MYN scheme),and 0.87%(BL scheme), respectively;for 2 m dewpoint temperature,only the mean RMSE by MYN scheme was reduced by 0.59%,while the mean RMSE of YSU,BL and ACM2 schemes increased by 1.39%,0.49%,and 0.89%,respectively;as to 10 m wind speed,only the mean RMSE by ACM2 scheme was reduced by 2.28%,while the mean RMSE of YSU,MYN, and BL schemes increased by 0.22%,2.32%,and 2.45%,respectively;for the vertical distribution of water vapor from sounding report,all of the four PBL schemes can successfully simulate the vertical distribution tendency of water vapor,but all results turned out to be much moister;by using STRM3 data,the vertical distribution of water vapor simulated by ACM2 scheme was improved on low layer during some periods of time.

Abstract:Based on radiosonde dataset from 105 stations in China,NCEP/NCAR reanalysis dataset,ERA reanalysis dataset and JRA reanalysis dataset,a study is performed on the reliability of the annual mean free atmospheric temperature from reanalysis datasets in China by means of linear analysis,standard deviation,correlation coefficient as well as EOF decomposition.Results suggest that:In numerical aspects,three reanalysis datasets are all lower than the observed dataset,and NCEP/NCAR dataset is much closer to the observed dataset in upper troposphere while ERA and JRA datasets are closer in middle and lower troposphere;In terms of annual and interdecadal trend,ERA dataset has higher ability to reproduce those trends in the upper troposphere in north region while NCEP/NCAR dataset is better in the upper troposphere in south region;Three reanalysis datasets have comparable ability in reproducing the trend in middle and lower troposphere;In the aspect of spatial and temporal variation characteristics,NCEP/NCAR and ERA datasets can preferably perform the feature of interdecadal variance while ERA and JRA datasets can reveal the characteristic of annual variance well.

Abstract:Based on DEM data of 1:250 000 scale and the data from 145 routine observation meteorological stations in Henan Province from 1961 to 2000,after fully considering the sky and rugged terrain elements,the paper realized the simulation of the spatial distribution of diffuse solar radiation(DSR) over rugged terrain in Henan Province with the extraterrestrial solar model and the terrain openness model.Monthly DSR and annual DSR at the resolution of 100 m×100 m over the rugged terrains in Henan Province were calculated.The simulated results show that,after fully considering the spatial-temporal characteristic coefficients,the simulated accuracy can be improved.The observation data from Zhengzhou indicate that the accuracy is high.The annual average error is 3.06 MJ·m^-2 and the annual absolute relative bias error is 1.67%.The local terrain can affect the DSR obviously.The annual average error of case year test is less than 11%.In summary,this model is good in spatial-temporal simulation.

Abstract:Because of response of the surface air flow to the distinct thermodynamic and dynamic disturbances by the complex topography in Guizhou Province,the convective-stratiform mixed clouds in which several convective cells imbed occur frequently.A typical convective-stratiform mixed clouds system in Guizhou Province on 29 May 2005 is studied in detail with observation data and simulation results.Results show that the convective-stratiform mixed clouds system is formed by cumulus merging and stratification,and the formation process goes through three typical merging stages.Precipitation is widespread with inhomogeneous distribution,and several strong centers embedded in rain field,which locate in small convective cells with the maximum precipitation of 60 mm.In the formation process of convective-stratiform mixed clouds,the ultimate cause why the intense precipitation occurs is that wind field and water content experience dramatic changes by release of instability energy during this process.

Abstract:The mechanism of hail formation and hail suppression technique are studied using the three dimensional hailstorm numerical model with fully elastic primitive equations,which is established by Institute of Atmospheric Physics,Chinese Academy of Sciences.The data used here are taken from a severe convective process with hailstorm and thunderstorm accompanied by gale occurred in Shandong Province on 5 July 2006.Simulation results show that 79% hailstone embryos are graupel particles,which are the main hail embryos.The dominant formation mechanism of graupel is the collision freezing of ice crystals,snow flakes with supercooled rain water and the auto conversion of snow.Once formed,the accretion of cloud water and rain water becomes the dominant growth mechanism of graupel particles.And the main growth mechanism of hail particles is the auto conversion of graupel and the accretion of supercooled cloud water.The results of seeding show that the growth of hail particles can be effectively inhibited if the seeding happens between one to four minutes before the hail content reaches 0.1 g·m^-3.And the seeding effect is better at 6.5—7.0 km heights than that at the other heights.Generally,the more AgI,the better seeding effect.Artificial ice crystals are produced with the sublimation nucleus AgI,and the sublimation growth of ice crystal results in decrease of the supercooled cloud water content.The number of hailstone embryos especially the graupel particles increases after seeding,and these numerous smaller hailstone embryos compete for the less available supercooled cloud water,so the average size and quality of hailstones decrease.The conversion rate of hailstone embryos to hailstones is reduced.The accretion of supercooled cloud water by hailstones decreases after seeding,resulting in decrease of the hail amount.

Abstract:This paper studies NO₂,SO₂,and O₃ at Linan in summer and winter of 2003 and 2004.Results show that the mean volume fractions of NO₂ and SO₂ are 19.48×10^-9 and 35.74×10^-9 in winter,respectively,which are higher than those in summer(4.81×10^-9 and 8.12×10^-9, respectively).The mean volume fractions of O₃ is 33.55×10^-9 in summer,which is higher than that in winter (25.44×10^-9).The volume fractions of NO₂ and SO₂ during the daytime are lower than those during the nighttime.The diurnal variation of NO₂volume fraction shows the single valley and single peak distribution with its peak during the nighttime.The diurnal variation of O₃ volume fraction is similar to NO₂,but its peak appears during the daytime.The volume fractions of NO₂ and SO₂ show an obvious "Holiday Effect",and are obviously lower during weekends than those during weekdays,with the highest on Fridays.The volume fraction of O₃ does not have an obvious "Holiday Effect".The wet removal efficiency of precipitation to SO₂ is more obvious than to NO₂.By contrast with the different wind directions,the higher volume fractions of NO₂ and SO₂ are affected by NW and WNW winds in summer,while by NE,SW and SSW winds in winter.The influence of wind direction on the ozone is complex,which is relevant to local photochemical reactions.