Based on the surface meteorological observation data from Chizhou station,the solid pre-cipitation processes in the winter half year of 2003-2019 are selected.According to T-mode principal component analysis(TPCA),the circulation situation in the winter half year is divided into three types:the one trough and one ridge type(Type Ⅰ),the zonal fluctuation type(Type Ⅱ)and the two troughs and one ridge type(Type Ⅲ).Type Ⅰ accounts for the largest proportion(45.2％),Type Ⅱ takes the second place(28.8％),and Type Ⅲ has the lowest percentage(25.9％).The solid precipitation in Chizhou region is mainly affected by the mid-way cold air.Four kinds of precipitation phases in the process of solid precipitation are summed up:rain,sleet,snow and direct snowfall.The gained sample numbers are 43 for rainfall,54 for sleet,39 for snowfall and 52 for direct snowfall,and their occurrence times are counted respectively.Then,according to the box-line plot method,the upper-air temperature of different layers,0 ℃ height,thickness stratification in ERA5 data and the ground temperature at the mete-orological stations are used for analysis,and the discrimination indexes are obtained and tested.The results show that when t1000hPa＜0℃,t925 hPa＜-3 ℃,t850hPa＜-3 ℃ and t2m＜0.8 ℃,rainfall tends to turn to snowfall;when t1000hPa＜-1.3 ℃ and t85ohPa＜-5.7 ℃,direct snowfall will occur.Temperature inversion generally exists in the middle and low layers.When 0 ℃ layer height is＜26 0 m(＞266 m),it is basi-cally pure snow(rain).The critical value of height for the conversion of rain and snow is 154 dagpm at H700-850hPa,for direct snowfall is below 153 dagpm,for pure snow at H850-1000hPa is below 129 dagpm and for direct snowfall is below 128 dagpm.The discrimination index of sleet is not clear,but the effect of ground temperature is relatively good.
关键词
降水相态/T-mode主成分分析/判别指标/箱线图/厚度层结
Key words
precipitation phase/T-mode principal component analysis/discrimination index/box-line plot/thickness stratification
维普
万方数据