台风数值预报中受云影响微波卫星资料的同化试验

目前, 数值预报中卫星资料的应用主要只是针对晴空条件, 大量受云和降水影响的卫星资料被丢弃不加以使用。但是, 云雨区观测往往包含有大量与天气系统发生发展密切相关的大气信息, 对这部分资料的同化应用由此成为当前研究的一个重要问题。在快速辐射传输模式中云雨粒子辐射效应的考虑还有待于进一步完善情况下, 云雨区卫星资料的应用通常是采用云检测方案对观测受云影响的严重程度进行判识并决定使用的取舍。以0604号热带气旋Bilis作为研究个例, 该文设计了一组受云影响微波卫星资料不同云检测方案和通道选择的应用试验。对AMSU-A资料, 云检测方案包括散射因子、降水概率和小雨检测3种, AMSU-B卫星资料的云检测方法选用了通道2亮温模拟观测误差和Bennartz散射因子。在对进入分析系统卫星资料与天气系统的配置关系、卫星模拟与实际观测偏差特征的统计以及对初始分析影响研究的基础上, 探讨了它们对台风不同阶段数值预报效果的影响。

The Use of Microwave Satellite Data Affected by Cloud in Numerical Forecast of Typhoon

Satellite data is being used in numerical weather prediction and takes up the role of main data source among the observations used. The quality of initial condition and the accuracy of numerical weather forecast are greatly improved by using satellite data. It is extremely important to use the satellite data in the numerical forecast of typhoon for there are few regular observations on the sea. However, only cloud-cleared satellite data is used in most current data assimilation systems because of the complexity to cope with the radiant effect of cloud and rain particles in radiation transfer model. The cloudy and rainy reg ion is always the sensitive area.The observation in these areas implies much information to weather system and has great impacts on the numerical forecast. There is a crucial need to handle the satellite data affected by cloud and rain in numerical weather forecast, but with caution at the same time. At present, the satellite data affected by cloud is examined through the cloud examination method.The No. 0604 typhoon Bilis is taken as a research case. A set of experiments are designed to use the satellite microwave data in cloudy area based on the cloud examination scheme. Scattering index, precipitation probability and precipitation examination are taken for AMS U-A. For AMS U-B, the bias between simulated bright tempe rature and observation of AMS U-B channel 2 and Bennartz scattering index are utilized. Different satellite data affected by cloud is used in data assimilation system by different cloud examinations and channel selection schemes.The screening of satellite data affected by cloud, together with their influences on the numerical forecast of Bilis's three periods, corresponding to formation, maturation and landing, is examined respectively. The result shows that more AMSU-A data is screened by scattering index than precipitation probability and precipitation examination. The scattering index with threshold 15 is suitable for the use of AMSU-A data in regional model. For AMSU-B, the bias between simulated bright temperature and observation of AMSU-B channel 2 performs better than Bennartz scattering index.