RTTOV散射模块在FY-3MWHS资料同化中的应用

Application of RTTOV Scattering Module to FY-3 MWHS Data Assimilation

一直以来,受同化系统中观测算子的限制,云区的卫星微波观测资料在使用时都常会做晴空假设,只考虑大气的吸收作用而忽略散射作用,从而会造成对大气中水汽含量的高估。为了克服这一缺点,文中设计了RTTOV微波散射模块在WRF-3DVAR系统中的应用方案,使得计算辐射能衰减的同时考虑大气的散射作用,并在此基础上通过4组试验进行了风云3-A星微波湿度计亮温以及多普勒雷达反射率因子的同化研究对比。结果表明:RTTOV微波散射模块的引入,能有效抑制晴空辐射模块对大气水汽含量的高估。若先同化雷达反射率因子后再继续同化卫星资料,会发现同化雷达后,同化区域内大气水凝物含量明显增加,受此影响同化卫星资料时大气的散射作用也会随之增大。并且雷达同化区域覆盖率越大,对降水预报的改善效果也愈明显。

All the time, because of the limits of observation operator in assimilation system, microwave observation over cloud area from satellite is often made clear hypothesis, which usually brings an overestimated content of atmospheric moisture. To overcome that, this paper designs a scheme to run RTTOV microwave scattering module in WRF 3DVAR for taking the information of atmospheric hydrometeors into assimilating calculation. On this basis, four groups of assimilation contrast tests are carried out for brightness temperature of FY3 A meteorological satellite microwave humidity sounder and reflectivity of Doppler radar. The results show that the introduction of RTTOV microwave scattering module can effectively suppress the overestimate of atmospheric water vapor content. When radar reflectivity factor is assimilated before satellite data, atmospheric hydrometeors content is increased significantly in this region. As a result, the scattering effects is increased too. With the area coverage of radar data assimilation increasing, precipitation forecast effect is improved more and more obviously.