TRMM测雨产品3B42与台站资料在中国区域的对比分析

本文利用2004—2008年6—8月中国673个气象站逐6小时降水资料检验同期TRMM测雨产品3B42的精度。经检验得出：卫星资料日平均降水和降水频率空间分布与台站资料非常类似,相关系数分别能达到0.79和0.84,降水频率与台站资料相比偏大;从日降水相关空间分布看,卫星资料在东部地区相关性较高,日降水相关系数都在0.6～0.9之间;从日降水和逐6小时降水平均绝对误差空间分布看,卫星资料在华南地区误差最大,长江流域次之;从中国8个区域逐6小时降水总量日变化看,卫星资料与台站资料有很好的一致性,但在华南地区20时降水量偏小;按不同雨量等级对比,发现卫星资料绝对误差相对百分率空间分布有如下特点：小雨全国普遍数值偏高,中雨东部部分地区偏大,大雨和暴雨整体上数值小于1;全国平均漏演率和空演率分别为10%和14%。     

A new weighting function for estimating microwave sounding unit channel 4 temperature trends simulated by CMIP5 climate models

A new static microwave sounding unit (MSU) channel 4 weighting function is obtained from using Coupled Model Inter-comparison Project, Phase 5 (CMIP5) historical multimodel simulations as inputs into the fast Radiative Transfer Model for TOVS (RTTOV v10). For the same CMIP5 model simulations, it is demonstrated that the computed MSU channel 4 brightness temperature (T4) trends in the lower stratosphere over both the globe and the tropics using the proposed weighting function are equivalent to those calculated by RTTOV, but show more cooling than those computed using the traditional UAH (University of Alabama at Huntsville) or RSS (Remote Sensing Systems in Santa Rosa, California) static weighting functions. The new static weighting function not only reduces the computational cost, but also reveals reasons why trends using a radiative transfer model are different from those using a traditional static weighting function. This study also shows that CMIP5 model simulated T4 trends using the traditional UAH or RSS static weighting functions show less cooling than satellite observations over the globe and the tropics. Although not completely removed, this difference can be reduced using the proposed weighting function to some extent, especially over the tropics. This work aims to explore the reasons for the trend differences and to see to what extent they are related to the inaccurate weighting functions. This would also help distinguish other sources for trend errors and thus better understand the climate change in the lower stratosphere.