Diagnosis And Analysis Of Precipitation And Important Weather Systems In The First Flood Season In South China

This article is studying the diurnal variations of precipitation in pre-flood season in South China during April to June in the period 2003-2016.Using hourly precipitation observation data from the 248 national ground weather stations which missing measurement data less than 10%.The multi-year average precipitation bands were studied separately according to topographic distribution.According to the onset and intensity index of South China Sea summer monsoon,the number of days before and after the onset will be determined.The rainfall period will be divided into two periods,before and after the onset.And analyzing the variation trend of onset and intensity index.According to the distribution of the rainbands,choosing radiosonde data of L wave band from 14 stations in the study area and interpolating the data based on height and time.Analyzing the influence mechanism of the daily variations of precipitation according to the spatial distribution of different thermal and dynamic factors at two moments(morning and evening)and their correlation with rainfall.Summarizes the primary coverage as follows to show:(1)According to the multi-year daily average precipitation analysis of the studied area,two main rainbands were obtained,and the space distribution of the two precipitation bands was used to screen radiosonde stations in adjacent areas.There are totally 14 stations were selected.(2)According to the onset of the South China Sea summer monsoon,the hourly precipitation observation data at the stations were divided into two periods before and after the outbreak.The correlations and standard deviations of the multi-year hourly average precipitation were studied.(3)Study the spatio-temporal changes of hourly precipitation amount,frequency and intensity and the changes in meridional mean and standard deviations over time.(4)Based on radiosonde data,the space-time changes of six kinds of precipitation-related thermal and dynamic factors were comparatively studied.The conclusion analysed above as follow: There are two major rainbands in South China: one locate at the south of the Yunnan-Guizhou Plateau and the Nanling Mountains,and the other is around the coastal areas of Guangdong.The northern rainbelt is mainly occurred from midnight to early morning,and the southern rainbelt is concentrated from noon to afternoon.There is no obvious correlation of precipitation between pre-and post-monsoon onset.While the relatively large correlation is mainly located from noon to afternoon and there is even a part of negative correlation coefficients.The standard deviations are mainly around 0.5 and mostly changed at early morning,as the smallest change is noon.The distribution of rainfall amount and frequency is similar: 112 oE is the transition.The westward maximum rainfall is located in the early morning,whereas the eastward mainly in the afternoon.According to the regional averaged normalized standard deviations of rainfall amount,frequency and intensity,the phenomenon of frequency in the early morning is unstable,while the occurrence of heavy rainfall event in the afternoon is unstable.They are obvious reduce at about 9 p.m.At post-monsoon-onset,the trends of them are almost the same.And there are two peaks,one in the early morning,the other in the afternoon,latter slightly larger.At the pre-monsoon-onset period,the rainfall pattern is high frequency on west and strong on south.The major influence of monsoon is strengthen intensity.While on the post-monsoon-onset period,the rainfall pattern is west north-east south south with high frequency and intensity.The monsoon mostly impact on increasing frequency.