TRMM揭示的南海不同回波顶高对流系统的季节变化特征

采用TRMM(Tropical Rainfall Measuring Mission)降水和云特征数据集,对南海2001年1月至2012年3月不同回波顶高对流系统的垂直结构、表面降雨率、数量时空分布的季节变化进行统计分析。结果表明:①浅对流、较深对流、深对流大于20dBz的回波区分别分布在4~8km、4~10km、4~14km之间;浅对流20dBz回波顶高的频率峰值为9km;冬季,较深对流、深对流20dBz回波顶高的频率峰值分别为13km、14.5km,其余季节偏高分别为14.5km、16km。②较深对流和深对流是南海地区面积平均降雨率较强的2种主要的降水系统;夏秋两季,较深对流的降雨率大于深对流;冬春两季,深对流的降雨率大于较深对流。③较深对流、深对流出现频次最少的季节为冬季,浅对流则为春季。④浅对流偏向于出现在12°N以南;深对流偏向于出现在12°N以北;较深对流在冬春季节集中在12°N以南,夏秋季节横贯南海。⑤夏秋两季在南海北部出现气旋性辐合上升的差异中心,南海中南部的西南水汽输送差异与700hPa以下水汽的辐合差异,是较深对流在夏秋两季比冬春两季带来更强降雨率的主要原因。

Seasonal Variation Features of Convections with Different Echo Top Heights in South China Sea Revealed by TRMM

Utilizing the TRMM precipitation and cloud feature database, the seasonal differences of vertical structure, area mean rainfall rate and spatial temporal distribution of precipitation for convective systems with different echo top heights over the South China Sea between January 2001 and March 2012 are analyzed. The results show that the reflectivity greater than 20 dBz of shallow, relatively deep and deep convections was respectively concentrated in 4-8 km, 4-10 km, 4-14 km, respectively. The frequency of 20 dBz echo top height peaked at 9 km for shallow convections. In winter, the frequency of 20 dBz echo top height peaked at 13.5 km and 14 km respectively for relatively deep and deep convections. However, in other seasons, their peaks were further higher arriving 14.5 km and 16 km. Relatively deep and deep convections were both two main precipitation systems with large rainfall rates in the South China Sea. Relatively deep convections have stronger rainfall rates in summer and autumn, while deep convections have stronger rainfall rates in winter and spring. Winter has the least number of relatively deep convections and deep convections, while spring has the least number of shallow convections. Shallow convections tend to occur in the south of 12°N and deep convections tends to appear in the north of 12°N. Relatively deep convections develop in the south of 12°N in winter and spring, but across the South China Sea in summer and autumn. For relatively deep convection events, there is a deviation center of cyclonic convergence in the northern South China Sea. The southwest water vapor transport difference in the central and southern South China Sea and the different convergence of water vapor below 700 hPa are the main reasons for stronger precipitation rate in summer and autumn than in winter and spring.