Abstract:In this study,numerical simulation and diagnostic analysis using model output data are conducted,in order to investigate the mechanism of track deflection of Typhoon Megi(2010) after its landing on Luzon Island.Next,the spectral nudging technique is adopted to reduce the error of the simulated large-scale environmental field.Based on the simulation results of the spectral nudging tests,terrain sensitivity tests are then conducted by varying the terrain height of Luzon Island.The temporal evolution of circulation structure and variable field are diagnosed to investigate the impact mechanism of high terrain on the typhoon track deflection.Finally,the southward movement when the typhoon approaches and lands on the island is displayed.The simulation results indicate that the simulation typhoon track of SNV700,which uses the configuration of nudging synoptic-scale wind component above 700 hPa,can reproduce the southward movement when the typhoon passes by the island and suddenly turns north after leaving the island,by reflecting both the steering role of large-scale environmental flow and the response of lower-level flow to the terrain.Based on the simulation results of the spectral nudging tests,terrain sensitivity tests are then conducted by varying the terrain height of Luzon Island.When the terrain height is reduced to zero,the simulated typhoon track is in correlation with the steering flow.The impact of high terrain leads the typhoon to turn to south(north) when the typhoon approaches(leaves) the high terrain,and the deflection degree increases as the terrain height increases.The results of the terrain sensitivity tests are diagnosed,and backward trajectory analysis of the affected areas is conducted,so as to investigate the temporal evolution of circulation structure and variable field when the typhoon approaches and crosses the island.The results show that the convergence center occurs in both the windward and leeward slopes,thus contributing to the gale center in these areas.In addition,a positive vorticity area occurs in the leeward slope,thereby indicating that secondary depression is induced,which appeals to the typhoon.Meanwhile,the outer and inner circulations of the typhoon are affected by the high terrain.The channeling effect contributes to the gale centers and confluent trajectories between the high terrain and typhoon center.The north(south) low-level jet in the windward(leeward) slope induced by the channeling effect leads the typhoon toward the south(north).

Abstract:Based on the Morphed Integrated Microwave Imagery data from Cooperative Institute for Meteorological Satellite Studies of University of Wisconsin and the best track data from Joint Typhoon Warning Center,the tropical cyclones(TCs) with secondary eyewall over the Northwest Pacific are examined.During 2005-2014,35 TCs with secondary eyewall are identified.The composited studies are performed to reveal the differences in environmental fields and initial structures between TCs with and without secondary eyewall (between fast and slow samples of secondary eyewall formation).Results show that both the environmental fields and initial structures can modulate the secondary eyewall formation.Specifically,the larger relative humidity of the environment field and the higher sea surface temperature,the easier the secondary eyewall will be formed.Furthermore,the formation rate of secondary eyewall is closely related to its own structure.A larger scale initial vortex leads to a faster secondary eyewall formation,father location of outer eyewall from typhoon center,longer duration of eyewall,and more dramatic intensity change before and after eyewall replacement.

Abstract:Precipitation type is often complicated when the ground temperature alternates between 0℃,and the its prediction has been one of the major difficulties in weather forecasting for many years.In this paper,four diagnostic methods are used to study the precipitation types,by examining the vertical temperature structure to be encountered by a falling hydrometeor,so as to diagnose a single type when the ground is reached.The four methods are the BTC algorithm,revised BTC algorithm,Ramer algorithm and Bourgouin algorithm.According to the ability of the mini-ensemble,the results with the majority of the algorithm/s outputs and more dangerous winter weather are integrated as the final precipitation type,including rain,snow,freezing rain and hail.The GRAPES_MESO mesoscale model is used to provide the parameters that the four diagnostic algorithms require.Next,the precipitation type's products are verified by two winter precipitation cases.Compared with the observation,it is shown that the revised BTC algorithm can correct the diagnostic bias of the original BTC algorithm for snowfall,and less hail is forecasted than when using the original algorithm.The Ramer algorithm obtains a greater number of freeze-rain events than several of other algorithms.The Bourgouin algorithm is closest to the results of the synthesis algorithm.Therefore,it is shown that the four schemes can reasonably predict the boundary line of rain and snow,as well as the areas of rainfall and snowfall.However,the scheme intentionally over-predicts hail and freezing rain,viewing these two types as more dangerous varieties of winter weather.
The results are directly related to the accuracy of the forecasted temperature profiles and precipitation areas in the model.These diagnostic schemes can only determine one type of precipitation,but cannot diagnose the sleet,thus at the junction of rain and snow there are a greater number of intermediate phases such as hail and freezing rain.The final integrated precipitation type of the four schemes shows the high probability and high influence of the various precipitation types,thereby providing effective warning information for disaster prevention and mitigation.

Abstract:Against the background of informatization,numerical weather prediction(NWP) has become an important means of meteorological prediction.The quality control of surface temperature observation data serves as the foundation of data assimilation,which is helpful for improving the accuracy of numerical weather prediction.Based on this,in this paper the B spline surface fitting algorithm is applied to the quality control of surface air temperature observation.Considering the spatial correlation between each reference station and target station with the region,a quality control algorithm for surface temperature observation data based on spatial correlation and B spline surface fitting(BSF) is proposed.Nanping,Nanjing,Taiyuan,Lasa,Jinghong and Changchun Stations are selected as the target stations,and the surrounding stations within 300 km are chosen as the reference stations.The time temperatures at 02:00,08:00,14:00 and 20:00 are selected as the observation data.BSF,SRT and IDW are used to control the quality of the target stations' surface temperature data.Combined with the mean absolute error(MAE),root mean square error(RMSE),index of agreement(IOA),nash coefficient(NSC) and rate of error detection,the results of the comparison lead to the conclusion that the BSF algorithm is able to effectively identify suspicious values in surface temperature observation data,and that it has a higher error detection rate and stronger adaptability than the traditional method.

Abstract:Increasing attention has been given to aerosols due to their substantial influence on the atmospheric environment,clouds and precipitation,and the climate.Atmospheric aerosols can serve as condensation nuclei for the formation of both cloud droplets and ice nuclei,and can alter the microphysical properties of clouds,which in turn affects the formation of rain,snow and other forms of precipitation.Many studies have been performed with the goal of furthering our understanding of the physical,chemical and optical properties of aerosol particles,along with their effects on cloud,precipitation and other weather phenomena.However,large uncertainties still remain in the study of the aerosol particles,in particular the vertical distributions of aerosols found in the lower troposphere.Therefore,there is a need to better understand aerosol vertical distributions.In addition,to better understand the impact of aerosols on clouds,it is crucial to determine the relationships between aerosols and cloud condensation nuclei(CCN).Aerosol particles which act as CCN,and their interactions with cloud droplets are the key uncertainties in determining the effects of aerosols on climate.Although researches including observations near the ground and many extensive aircraft measurements have previously focused on the activation properties of aerosols and CCN,more direct and long-term observations are required to simultaneously characterize height-resolved aerosol,CCN and clouds properties,as well as to provide essential validation for modeling and satellite remote sensing.Using the aircraft as the observation platform by which to carry the instruments can effectively solve these problems.In the present study,in-situ aircraft measurements of aerosols and CCN of 11 flights during the spring and summer of 2010 in the Shijiazhuang area were analyzed,including the comparison of the vertical distribution of aerosol particles,particle size distribution at different heights,and the vertical distribution and activation characteristics of CCN under both cloudy and clear conditions.The results show that the mean aerosol number concentration(N_a) under cloudy conditions is 1 553.28 cm^-3,and the mean effective diameter (D_e) is 0.52 μm,which is 76% larger than that of clear sky (N_a:883.82 cm^-3) and 41% for effective diameter (D_e:0.37 μm).Under cloudy conditions,N_a decreases exponentially with height,and the particle effective radius (R_e) does not change significantly at heights below 2 500 m,however it increases gradually at heights greater than 2 500 m.Under clear sky,N_a accumulates in the height range of 800 to 1 500 m,while R_e does not change significantly with height.The shapes of the aerosol number size distributions remain almost the same at different heights,and have a successive distribution for smaller particles (<0.3 μm) under both cloudy and clear skies,with a sharp decrease at 0.3 μm.Above 2.5 km,N_a is lower under cloudy sky than clear sky,while in the near-surface layer and boundary layer N_a is higher under cloudy sky than clear sky.For both skies,the number concentration of CCN (N_CCN) decreases with altitude at each observation height,and is higher under cloudy sky than clear sky.The activation ratio of CCN(N_CCN/N_CN) does not change significantly with height under cloudy conditions,however it increases with altitude under clear sky.Particle size and N_CCN/N_CN have a positive linear correlation.

Abstract:Based on the national air quality index(AQI),the ground-based PM_2.5 data,the global assimilation system GDAS data and FNL reanalysis meteorological data,this paper studies the variation characteristics of air quality,environmental transport conditions and pollutant sources in the northern suburbs of Nanjing in the winter of 2015/2016.Results indicate that,represented by AQI,there are three typical pollutant transregional transport routes for winter pollution in Jianghuai area,and they are the northwest,north and southwest routes.The northwest route usually occurs at the time when the Mongolian high is strong and locates at the climatological position.At the same time,there is cold advection over the northern suburbs of Nanjing,which is not conducive to pollutant diffusion.The north route corresponds to weak Mongolian high and weak high near Northeast China.The northerly airflow brings pollutants to the northern suburbs of Nanjing.If it crosses the ocean,the pollutions will be reduced.The southwest route corresponds to the anticyclonic circulation center in the boundary layer in the northern suburbs of Nanjing,and the sinking airflow is very unfavorable for pollutant diffusion.The potential sources of pollution in the northern suburbs of Nanjing are mainly located in southern Hebei,western Shandong,southern Henan,eastern Anhui and western Hubei.Hebei Province is a crucial pollution source area,and the pollutants in southern Hebei and western Shandong are transported to the northern suburbs of Nanjing through the north route.Therefore,although the north route has less pollution probability than the other two routes,it is an important route to form severe pollution in the northern suburbs of Nanjing.Besides,pollutants in southern Henan are transported through the northwest route,and pollutants in Anhui and Hubei are transported through the southwest route.Quantitative analysis shows that the advection transport is an important cause of serious pollution in the northern suburbs of Nanjing.The contribution of near-surface wind speed to AQI advection is more than 70% or even 85%.

Abstract:Based on the WRF mesoscale numerical model and by using the initial cloud condensation nuclei(CCN) data in NSSL(C=600 cm^-3、k=0.6)and the observation fitting data from the northern suburbs of Nanjing(C=4 000 cm^-3,k=0.47),the paper simulated a strong convective weather event in Anhui Province.The maximum simulated radar reflectivity of CASE1 was 50-55,while that of CASE2 was 55-60.,It was closer to the actual situation in CASE2 than in CASE1 in terms of intensity and width of the cloud,and CASE2 reflected stronger echo.The precipitation area of CASE2 was closer to the reality than that of CASE1,and the precipitation intensity was stronger than that of CASE1.The occurrence of multiple strong echoes made the distribution of heavy rainfall area wider in CASE2.In early stage of CASE2,larger cloud water and ice crystal particle number concentration released more heat when the water particles were frozen and thus made the cloud develop more vigorously than in CASE1.The snow crystal mass and number concentration were similar in the two cases.In CASE2,the water content ratio of graupel and hail particles was higher than that in CASE1,and thus produced stronger cold could precipitation in melting process.

Abstract:Based on the observed precipitation,sea surface temperature and NCEP/NCAR reanalysis data from 1979 to 2015,this paper analyzes temporal features of Nanjing summer precipitation.Results indicate that the precipitation has obvious interannual and interdecadal variations,with an overall increasing trend.In 1991,summer precipitation in Nanjing is an extremely positive anomaly,with the anomaly of 343.92 mm,while the precipitation in 1994 is a negative anomaly,with the anomaly of -273.78 mm.There is a significant negative correlation between summer precipitation in Nanjing and sea surface temperature anomaly(SSTA) in the subtropical Northeast Pacific(west coast of California,USA).SSTA in subtropical Northeast Pacific is negative in 1991 and no significant in 1994.The negative SSTA in the subtropical Northeast Pacific in 1991 causes the low-level divergence and high-level convergence over the region,and the low-level convergence and high-level divergence over the tropical Middle East Pacific.Such circulation anomalies cause abnormal upward motion over the Middle East Pacific Ocean.The abnormal upward motion causes sinking motion near the Philippines and inhibits convective activity in the region through zonal vertical circulation,triggers negative EAP/PJ teleconnection wave train,and causes positive precipitation anomalies in the Yangtze River basin,including Nanjing.At the same time,water vapor is transported and converged from Philippines to Nanjing,which is conducive to more precipitation in Nanjing in the summer of 1991.In 1994,there is no significant SSTA in the subtropical Northeast Pacific,and the convective activity near the Philippines is active,which triggers the positive anomalous EAP/PJ teleconnection wave train.Meanwhile,water vapor is transported westward from the Kuroshio extended area through the Japanese islands,and Nanjing region is a water vapor divergence area,which makes the summer precipitation in Nanjing negative anomaly in 1994.

Abstract:Based on the monthly CCMP sea surface wind speed data,the wind speed data from coastal meteorological stations and the NCEP/NCAR reanalysis data from 1988 to 2017,this paper analyzes applicability of CCMP sea surface wind speed data in coastal areas of Zhejiang Province,and interannual variation characteristics and possible causes of sea surface wind speed in coastal areas of Zhejiang Province.Results show that:by comparing CCMP sea surface wind speed data with sea surface wind velocity data observed by typical coastal meteorological stations(Shengsi,Putuo,Dachen,Yuhuan and Dongtou stations) in Zhejiang Province,the wind speed trends of the two sets of data are basically the same,and the deviation between the two sets of data is small.It is reasonable and credible to study the interannual variation characteristics of wind speed in Zhejiang coastal area by using CCMP sea surface wind speed data.Empirical orthogonal function(EOF) analysis results of CCMP wind speed anomaly field show that:the variance contribution rate of the first mode is 90.9% and the spatial field shows a consistent pattern;the variance contribution rate of the second mode is 6.09% and the spatial field shows a dipole variation pattern.According to the variance contribution rate of the first mode and its spatial field distribution,the wind speed in the whole coastal area of Zhejiang Province can be studied as a whole.The annual average wind speed series of Zhejiang coastal CCMP from 1988 to 2017 shows that the coastal sea surface wind speed has changed from rising to falling before and after 2002.The analysis of land-sea temperature shows that the possible reason for the change of sea surface wind speed in Zhejiang coastal area is that the land temperature rises too fast.

Abstract:Based on the NCEP/NCAR daily reanalysis product and daily precipitation and temperature data collected at observational stations,the circulation characteristics and causes of anomalous the high temperature and drought in the summer of 2018 over Liaoning Province have been investigated using a diagnostic analysis method.The results demonstrate that in the summer of 2018 Liaoning Province experienced a record-breaking event since 1962.The precipitation in the entire region showed a negative anomaly,and the anomalous precipitation was -127.72 mm.The precipitation anomaly percentage in the western and eastern parts of Liaoning Province was 10%~30%,while that in the central part was 30%~60%.In particular,the precipitation anomaly percentage in the northern and southern parts of Liaoning Province was less than 60%.Meanwhile,unusually high temperature influenced Liaoning Province mainly from mid-July to early August.The high temperature was developing from the northeastern part of Liaoning Province and gradually spreading to the southwestern part while strengthening in intensity,and reaching its peak in early August.The temperature in the northern part of Liaoning Province was more than 2.4 degrees greater than its mean climatology;that in the central part was more than 3.2 degrees greater;and that in the southern part was more than 4 degrees greater.Under the influence of abnormally high temperature and abnormally low rainfall,the drought situation in Liaoning Province intensified rapidly.The anomalous anticyclonic circulation with equivalent barotropic structure is the local circulation cause.Liaoning Province was controlled by an abnormal anticyclone from the lower troposphere to the upper troposphere.The anomalous cyclonic circulation on the southern side of the anomalous anticyclonic circulation blocks the warm and humid airflow from the Bay of Bengal and South China Sea to Liaoning Province,which is conducive to precipitation in Liaoning Province.Moving in opposite directions of the South Asia High(SAH) and Western Pacific Subtropical High(WPSH) and overlapping over Liaoning Province was the large-scale circulation caused by the hot and drought-ridden summer of 2018.As a result,Liaoning Province was continuously affected by the downdraft.The East Asia Pacific/Pacific Japan (EAP/PJ) and Eurasian (EU) pattern was one of the direct causes for the abnormal development of the WPSH.The positive geopotential height anomaly center in Liaoning Province was strengthened by the EAP/PJ and EU pattern,thus contributing to the northward positioning of the WPSH.The dispersion of Rossby wave energy is one of the fundamental causes for the formation and perpetuation of the EAP/PJ and EU pattern.The Rossby wave energy originating from the North Atlantic dispersed eastward to East Asia along the waveguide area of the high-altitude westerly jet,thereby resulting in the abnormal enhancement of the geopotential height in northern China,including Liaoning Province.Meanwhile,there was a quasi-meridional dispersion of Rossby wave energy from northeastern China to the Korean Peninsula and Japan,which is conducive to maintaining and developing the EAP/PJ and EU pattern,thus making Liaoning Province controlled by a positive geopotential height anomaly,and in turn the WPSH developed abnormally.The persistence of the heat and drought event over Liaoning Province was due to the perpetuation of the quasi-stationary waves at mid-high latitudes,which originated from the North Atlantic Ocean.

Abstract:The development and evolution of a thunderstorm triggered by a sea breeze front on 28th July 2016 in Hangzhou Bay was studied by numerical simulation using the high resolution mesoscale model WRF,conventional meteorological data,Doppler radar data,encrypted data of Zhejiang Automatic Station and NCEP/FNL reanalysis data.The results revealed the following:1) The sea breeze front is the main trigger system for the thunderstorm.2) The numerical simulation with WRF can accurately reproduce the precipitation of the thunderstorm and the horizontal and vertical structure of the sea breeze front.3) There are evident promoting effects on the strengthening of the humidity and vorticity characteristics of the sea breeze front,which provides favorable water vapor and dynamic conditions for the occurrence and development of the thunderstorm.4) Analysis of the mutation position of the evolution curve of the convective parameters exhibits certain indication and prediction significance for the time of thunderstorm occurrence.Only one sea breeze front on the southern side of Hangzhou Bay can also trigger a thunderstorm.

Abstract:In this study,by using the Weather Research and Forecasting(WRF) model with five different planetary boundary layer options(no planetary boundary layer scheme,Yonsei University scheme,Mellor-Yamada-Janjic scheme,asymmetric convective version 2 scheme and medium-range forecast scheme),a rainstorm which occurred in July 2013 in the Yangtze River area was simulated.Through comparison with the observation data,the respective simulation capabilities of the five different experimental designs were evaluated.Then their simulated precipitation area,total rainfall amount,and basic meteorological elements were analyzed.The observations show that the simulated results obtained using the various schemes are different.The rain band's general trend can be accurately simulated,regardless of whether or not the PBL parameterization schemes are used,yet the simulations of the intensity and location of the rainfall center differ to some extent.The largest rainfall simulation bias occurs in the experiments performed without the planetary boundary layer scheme,while the experiments performed with the asymmetric convective version 2 and medium-range forecast schemes produce better rainfall simulations.In particular,the experiment using the Mellor-Yamada-Janjic scheme yields the best simulation results for small and large rainfall,while when coupled with the Yonsei University scheme,the model yields the highest threat score (TS) for the simulation of rainfall with various intensities.Through the analysis and comparison of various physical quantities,the following conclusions are drawn:1)Compared to the other schemes,the simulation results of the MYJ scheme are closer to the observed values;2)The MYJ scheme can simulate two water vapor transport channels:one is dominated by southwesterly wind,with strong convergence of south wind speed at the exit of the jet stream,which drives the water vapor coming from the southwest converge to the rainstorm area;while the second conveys the water vapor from east to west to ensure the local convergence of the rainstorm area;and 3)The vertical motion center and precipitation area from the MYJ and YSU schemes are similar,but the YSU-simulated rising speed is larger,thus in comparison the MYJ scheme is more reasonable.

Abstract:Atmospheric temperature and humidity profiles are important atmospheric parameters and play an important role in numerical weather forecasting and weather warning.In order to obtain high-precision profile data of atmospheric temperature and water vapor mixing ratio,this paper studied a variational retrieval method of atmospheric temperature and water vapor mixing ratio profiles based on the Metop-A/IASI infrared hyperspectral data.Based on the radiance data of IASI hyperspectral sensors,combined with the forecasting technology of CRTM model and WRF model,using one dimensional variational method,this paper studied the quality control of satellite data,background error covariance localization and observation error covariance methods,constructed a variational retrieval system for atmospheric temperature and water vapor mixing radio profiles,and carried out the retrieval tests in Beijing,Qingdao and Shenyang.Comparison of retrieval results with sounding data as a standard shows that,using the WRF model forecast values as the background field,the average absolute error of temperature(water vapor mixing ratio) is less than 0.6 K(0.021 g/kg),and the root mean square error is 0.89 K(0.02 g/kg).The experimental results show that based on the one dimensional variational method,the Metop-A/IASI infrared hyperspectral data can be used for the high-precision detection of atmospheric temperature and water vapor mixing ratio profiles.

Abstract:In this study,based on routine weather and Doppler weather radar data,the characteristics of the synoptic circulation background and structure characteristics of the supercell hailstorm which had occurred in Xuzhou are analyzed.The results show that this event had a forward-tilting structure,namely the upper-level trough moved from west to east at 500 hPa,and the cold air moved toward the south interface with the low-level jet,which was favorable to the formation of an unstable stratification structure.The convective storm that caused the hail had a typical supercell structure,and a strong rotation mesocyclone.The mesocyclone lasted nearly 30 minutes,and the max shear level of the mesocyclone was continuously higher than the 0℃ thermal level.Further research found that the max values of the rotational velocity and azimuthal shear of the mesocyclone were in the middle and upper levels,the rotation of the storm tended to expand upward,and the rotation had an abrupt increase in middle and upper levels.The rotation in the middle and upper levels of the storm underwent a process of decreasing in size,and the rotation intensified before and after the hail occurred,while the rotation in the storm led to the characteristics of suspended high strong echo and prominent bounded weak echo.In addition,the vertically integrated liquid (VIL) was much lower in this hail event,yet the vertically integrated liquid (VIL) underwent an abrupt increase before and after the hail occurred.This phenomenon can help us to judge the occurrence of small hail in the future.

Abstract:The southwest vortex is a special weather system that forms on the east side of the Tibet plateau.However,at present there is no uniform standard for the identification of the southwest vortex.In this study,based on the analysis of the main features of the southwest vortex,the HVW identification method which is suitable for the southwest vortex is designed,by combining the height,vorticity and wind.This method is then applied to the GRAPES-MESO high-precision grid analysis data from June to August in 2014,and the paper compares the difference between this method and the actual situation of the southwest vortex on the weather chart.Through the analysis of the identification of the southwest vortex,the generation and demise time,the center of the vortex and its strength,the following conclusions are obtained:(1) The HVW identification method can effectively identify the high-precision grid data in the southwest vortex process,and the coincidence rate with subjective analysis on the grid data is 87.5%.In addition,the accuracy of HVW identification method can reach 90.9% in the case of the southwest vortex,which can be reproduced in both the weather map and grid data,thereby indicating that the HVW identification method can effectively capture the southwest vortex.(2) The HVW identification method can reasonably analyze the generation and demise time of the southwest vortex life time.(3) The analysis of the location deviation of the southwest vortex center shows that the southwest vortex center position of the HVW is located near the southwest low vortex pressure,and that it is also located within the convergence center of wind field.(4) The evaluation of the strength of the southwest vortex center shows that the difference between the subjective analysis on the grid data and the HVW method is almost negligible,which reveals that the HVW identification method contains the height information of the grid data.The southwest vortex center intensity of the recognition method can be used instead of the subjective analysis of the grid data.In this paper,the analysis of the southwest vortex process from June to August,2014 is carried out to verify the feasibility,rationality and accuracy of the HVW stepwise cyclic location method.Compared with the subjective visual analysis of the weather map,it is shown that this method can effectively identify the southwest vortex weather system,reduce the error caused by the subjective analysis,and reduce the workload of the business analysis.

Abstract:Imperative quality control methods for Doppler radar data,such as ground clutter elimination,range folding elimination and velocity dealiasing,should be adopted before being used for quantitative analyses,due to the serious impacts originating from certain non-meteorological factors.In this study,in order to precisely identify the ground clutter and precipitous echo,an automatic algorithm based on the Support Vector Machine(SVM) is performed,based on the observational CINRAD/SA Doppler weather radar data in the areas of Anqing and Changzhou from June to August,2013,and the results are compared with the recognition effect based on the Artificial Neural Networks(ANNs) method.Statistical learning theory(SLT) is favorable for small samples,which focuses on the statistical law and nature of small-sample learning.As a new machine learning based on SLT,the basic principle of the SVM is to possess an optimal separating hyperplane which is able to satisfy the requirement of the classification accuracy by introducing the largest classification intervals on either side of the hyperplane.In the first step,the dataset used in the experiment will be establised by empirically distinguishing the ground clutter and precipitous points at each bin.Next,several characteristic parameters,which are used to quantify the possibility affected by the ground clutter,such as reflectivity vertical variation (G_DBZ),reflectivity horizontal texture (T_DBZ),velocity regional average (M_DVE),and spectrum regional average (M_DSW),will be derived from the reflectivity,radaial velocity,spectrum width and spatial variance information of the ground clutter and precipitous echo.The statistical results of the above characteristic parameters show the following:a large portion of these parameters vary in terms of ground clutter and precipitous echo,which indicates that the seven parameters (G_DBZ,T_DBZ,S_PIN,S_IGN,M_DVE,M_DSW and S_DVE) contribute to the identifiable recognition of the ground clutter and precipitous echo.Based on the above conclusions,seven parameters,which are regarded as the trigger (the training factor of SVM) to establish the SVM's training model,can be randomly extracted from the database.Finally,the training model is used to automatically recognize the ground clutter and precipitation using the random data from the database.The recognition effect of the SVM method will be examined by comparing the model output with the empirical identifications,and the examination of the ANNs algorithm is the same as that of the SVM method.The comparison of the recognition effect between the SVM and ANNs methods reveals the following:(1) The statistically identifiable recognition parameter for the sSVM and ANNs methods appears to be steady,despite the fact that the Doppler radar data vary in shape and position between Anqing and Changzhou;(2) An identifying threshold must be determined for the ANNs method before the ground clutter and precipitous echo are identified,which will lead to a differently identifiable accuracy with the unlike threshold;and (3) Overall,the SVM method works better than the ANNs method in terms of radar echo identification.Moreover,the identifiable recognition accuracy of the latter increases significantly with the increasing total number of training samples,while the identifiable recognition accuracy of the former performs at a highly accurate level,which remains relatively stable with the changes in the training samples.In terms of the identification accuracy of the total samples (ground clutter and precipitous echo) and identification accuracy of the ground clutter echo,the SVM method presents better results than the ANNs method.As for the precipitous echo erroneous recognition,the ANNs method performs slightly better than the SVM,but both methods control the erroneous recognition rate at a low level.