利用TRMM卫星分裂窗通道对东亚地区夏季降水判识方法的探索

Exploration on the Summer Precipitation Detection over East Asia Using Split Window of TRMM Satellite

利用2005年9月东亚中低纬地区的63个时次的TRMM卫星资料,分析了降水云和非降水云的红外辐射特征。结果显示:10.8μm通道大部分非降水像元的亮温大于280 K,晴空像元的亮温更高;大部分降水像元的亮温小于280 K,降水越强亮温越低,强降水的亮温在260 K以下。非降水像元的分裂窗通道亮温差(BTD45)总的来说都高于1.5 K;降水像元的BTD45总的来说都小于3.0 K,强降水像元BTD45较低,一般在2.0 K以下。在此基础上,分析了中低纬度夏季6次的不同类型的大尺度短时强降水数据,得到了中低纬度夏季强降水过程中非降水云和降水云对应的红外辐射特征,并以此为依据,提出BTD45为3.0 K和10.8μm通道亮温260 K为降水识别阈值,二者结合,可以得到较好的降水判识结果。

This study diagnosed 63 orbits of TRMM satellite data in the low and middle latitude over the East Asia during September 2005 and analyzed infrared radiation characteristics of rain and no-rain clouds. The results indicated that the brightness temperature （BT） of most no-rain pixels in 10.8μm channelis usually above 280 K,while that of the rain pixels is usually below 280 K. Generally speaking, the BT of the no-rain pixels is much higher under the clear sky, and the BT of the rain pixels is lower for the heavier precipitation. The BT of the rain pixels for the heavy precipitation is usually below 260 K. The bright temperature difference between the split window （BTD45） of almost all no-rain pixels is above 1.5 K,while the BTD45 of rain pixels is usually below 3.0 K. The BTD45 for the heavy precipitation is usually below 2.0 K. Six different typical large scale heavy precipitation events occurred in the low and middle latitude of East Asia during summer are further analyzed in order to obtain the infrared characteris- tics of the no-rain and rain clouds during the heavy rainfall processes for this region. The results suggested that most of the precipitation pixels could be detected using the combined thresholds of the BT below 260 K in 10.8 μm channel and BTD45 below 3.0 K.