| Precipitaiton is an important component of the geographic information.Study on the classification of precipitation types and convection intiation(CI)will help people improve the knowledge of laws of atmospheric motion in the earch surface system.This study classifies precipitaiton over China into three types(convective precipitation,stratiform precipitation and snowfall)based on radar reflectivity mosaic images and ERA5-Land reanalysis data,and investigates the spatiotemproal distribution characteristics of these precipitation types at different time scales from September 2017 to August 2021,as well as further identifies convective initiation(CI)during the study period to reveal the spatiotemproal characteristics of convective initiations over China.This study demonstrates the characteristics of different precipitation over China from the perspective of radar observations,which is expected to be a reference for the study of precipitation characteristics in China and a potentially useful database for meteorological and hydrological prediction applications in China,and would act as a critical part of the background database for meteological geographical information system.The main conclusions of the paper are as follows:(1)The eye-inspection of the Chinese radar reflectivity mosaic images resulted in 98.35%data integrity after removing damaged radar mosaic images.The radar mosaic data are used to built the Chinese radar reflectivity mosaic dataset from September 2017 to August 2021 based on the background processed radar reflectivity mosaic data.Based on the method of distinguishing precipitation by thresholds and the classification of snows in NSSL ’s(National Aeronautics and Space Administration)radar-based quantitative precipitation estimation system,this study classifies precipitation into three categories,i.e.convective precipitation,stratiform precipitation and snowfall,with ERA5-Land data as auxiliary data,and explores the characteristics of spatiotemproal distribution variation of different precipitation types in China.In addition,in order to better understand the development and variation characteristics of convective precipitation in China,this study firstly compares the identification results of CI identification framework before and after the improvement.Based on the spatial distribution and case comparison,it is found that the improved CI identification framework can better identify the location and occurrence time of CI,which can be applied to identify the spatiotemproal variation characteristics of convective initiation in China during September 2017 to August 2021.(2)The spatial and temporal distributions of the three precipitation types vary at different times,showing pronounced seasonly variations and regional characteristics.The spatial distribution of both convective precipitation and stratiform precipitation is closely related to the development of the East Asian summer monsoon and topography.Above 80% of convective precipitation and stratiform precipitation occurs from April to September,which corresponds to the time of the flood season in South China and the Meiyu period.Convective precipitation is mainly distributed in southern China,and the most intensive precipitation centers of convective precipitation are located in the Pearl River Delta(PRD)and the Yangtze River Delta(YRD).Stratiform precipitation dominates the total precipitation occurrence throughout the year,and its occurrence ratio is much higher than convective precipitation and snowfall.After the onset of East Asian summer monsoon in May,convective precipitation and stratiform precipitation increase significantly and expand northward,in addition to convective precipitation expanding northward and inland along Chinese coastline.Therefore,the PRD becomes the largest precipitation center of convective precipitation earlier than the YRD.Due to the increasing convective precipitation,its percentage also increases and reaches its peak in July.This leads to a decrease in stratiform precipitation after its peak in May,but it starts to increase gradually in July and peaks again in August.Snowfall is mainly distributed in the high-altitude regions of northwest China,primarily occurring from November to March,with the boundary of "Hengduan Mountains-Qinling Mountains-Taihang Mountains-Liaodong Peninsula" showing the spatial distribution characteristics of high occurence in the northwest and low occurence in the southeast.(3)Convective precipitation is concentrated in the night to early morning from November to March,and in the daytime from April to October,reaching its major peak in the late afternoon(15-17 LST).Strong convective precipitation in the PRD often occurs in the late afternoon,whereas that in the YRD often occurs from midnight to early morning.Meanwhile convective precipitation centers initially appear in coastal areas during the flood season and gradually expand inland due to sea breeze activity and thermal properties difference between the land and the sea,and peak in the late afternoon(12-19 LST).Stratiform precipitation has a strong diurnal variation characteristic in April-November,often occurring in the late afternoon to night(15-06 LST).During the flood season,stratiform precipitation occurs more frequently in the night to morning(21-11 LST)than in the afternoon(12-20 LST)along the coast.Snowfall often occurs from night to morning(20-10 LST)and peaks between midnight and morning(02-08 LST).(4)The CI is mainly distributed in the southern coastal regions,while the offshore areas have a much lower occurrence of CI than the coastal land.The offshore CI mostly occurred at night to early morning(00-06 LST),and on land CI basically occurred during daytime(09-18LST).From April to September,CI accounts for more than 90% of the annual total.In August,CI had the highest monthly average(1,731).The development of East Asian summer monsoon and topography have pronounced effects on CI.The highest frequency of CI diurnal frequency is initially located in Hainan,and CI continuously expands northward with the summer wind after April.The high CI frequency value area also expands northward on land as well as northeastward along the coastline,forming a CI rain belt along the southeast coast of China.Meanwhile,the variability of CI in Taiwan and the Tianshan Mountains shows that summer winds and topography have a close relationship on CI.The CI decreases significantly after the receding of summer winds.From March to September,most of the CIs over land gradually move from night-morning(21-08LST)to early afternoon(12-15 LST).In particular,from June to September,a midnight-early morning(00-06 LST)CI rainband gradually moves from the "Sichuan Basin-Shandong Peninsula-Northeast China" to the " North-central Guangxi-Yangtze Delta".(5)The daily variation of CI is more similar from April to September,becoming increasingly active from 09-10 LST and peaking at 12-13 LST.In contrast,the daily variation of CI is more stable from October to March.In addition,the peak time of CI occurs 2-4 h earlier compared to the peak time of convective precipitation which often occurs in the late afternoon(15-17 LST),indicating that about 2-4 h are experienced from the beginning of convective precipitation to the development of strong convective precipitation. |
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