华南前汛期大范围暴雨的合成分析

A COMPOSITE ANALYSIS ON WIDESPREAD TORREN-TIAL RAINFALLS DURING FIRST RAINY SEASON IN SOUTH CHINA

摘要:

根据广东1959—1982年前汛期13次大范围暴雨过程的普查分析结果,发现这些暴雨过程全部与低空急流密切相关。选取850百帕的大风核中心点为基准,计算了18—30°N,105—120°E间的合成气象场,得到两类大范围暴雨的主要特征,指出了大风核附近的气象要素与广州站5—6月多年平均状态的差别。最后,作了简短的讨论,并给出简要的结论。

Abstract:

There are two rainy seasons in one year in South China. The first rainy season includes April, May and June. After an investigation on thirteen widespread torren-tial rainfalls during the first rainy seasons in South China in 1959-1982. it was found that all the torrential rainfall events analysed in this paper closely related to the low level jet. So, the strong wind cores at 850 hPa are chosen as the datum point with composite technique and the composite meteorological element fields are presented in the area between 18-30°N and 105-120° E. From these data, the widespread torrential rainfalls are grouped, by wind field, into two categories. Consequently, the main characteristics of each category and the differences of meteorological elements of the area near the strong wind core in comparison with the mean value of Guangzhou in May and June are given reazonably.After a brief discussion, the elementary conclusions are presented as following:1. The composite technique using the center of strong wind core of the low level jet as a datum point is shown to be working reasonably.2. The main rainfall occurs in the warm sector and left side of the low level jet (within two latitude degees).3. The meteorological element fields of widespread torrential rainfalls are cha-ractized by:(1) lower 700-500 hPa temperature and nearly the same temperature at 850hPa, in relation to the mean values of their respective layers in May and June in Guangzhou.(2) positive anomaly of dewpoint temperature in the left side of the low level jet, especially at 700 hPa.(3) high specific humidity(over 13.5g/kg in 850 hPa,9.0g/kg in 700 hPa and 4.0g/kg in 500 hPa).(4) evident positive variation of dewpoint temperature in 24 hours in 700-500 hPa.(5) Coupling of convergence and positive vorticity at low level, especially in the type II torrential rainfalls.4. The objective analysis of wind field is necessary since the low level jet is important in heavy rain forecast and it is difficult to set an accurate orientation in synoptic maps.