FY-3D卫星MWHS-2辐射率资料直接同化对台风“米娜”预报的影响

Assimilating MWHS-2 radiance of FY-3D satellite and its influence on the forecast of Typhoon Mitag

文章基于天气研究和预报(weather research and forecasting,WRF)模式中的FY-3D卫星微波湿度计Ⅱ(micro-wave humidity sounder 2,MWHS-2)辐射率资料的直接同化模块,采用三维变分(three dimensional variation,3DVar)方法在晴空条件下同化MWHS-2辐射率资料,考察MWHS-2辐射率资料同化对台风“米娜”(2019)预报的影响。文中设计了4组试验,第一组试验不同化任何资料,第二组试验同化了单独的全球通信系统(global telecommunications system,GTS)常规资料,第三组试验联合同化了GTS常规资料和MWHS-2辐射率资料,第四组试验将MWHS-2辐射率资料换成先进技术微波探测计(advanced technology microwave sounder,ATMS)辐射率资料同化。研究结果表明:偏差订正后各通道观测和背景场差值的均值趋于0,同化后分析场相对观测的标准差与均方根误差较背景场显著减小,同化过程是有效的。与仅同化GTS常规资料和同化ATMS资料的试验相比,同化晴空MWHS-2辐射率资料后的增量场在台风中心附近有负的高度增量和正的温度增量,从动力与热力上有助于台风的维持。在确定性预报最后的12h,同化晴空MWHS-2辐射率资料的试验能够改进500h Pa环流形势的模拟,加强西南方向引导气流的强度,从而最终减小台风路径预报的误差。

Based on the module of directly assimilating MWHS-2(microwave humidity sounder 2)radiance of FY-3D in the WRF(weather research and forecasting)model,this study investigates the influence of assimilating clear-sky MWHS-2 radiance on the forecast of Typhoon Mitag(2019)by using the 3DVar(three dimensional variation)assimilation method.Four experiments are designed.No assimilation is performed in the first one,while only GTS(global telecommunications system)data are used in the second one.Further,the assimilation of both GTS data and MWHS-2 radiance is carried out in the third one.The fourth one replaces MWHS-2 radiance with ATMS(advanced technology microwave sounder)radiance.The results show that the mean differences of all channels between the observation and the background verge to 0 after the bias correction.In addition,compared with the background field,the standard deviation and root mean square error of the analysis field versus the observation decrease significantly after the assimilation,which demonstrates the effectiveness of assimilation.Compared with the experiment only assimilating GTS data and the experiment assimilating ATMS radiance,a negative height increment and a positive temperature increment are observed near the typhoon center after assimilating clear-sky MWHS-2 radiance,which contributes to the maintenance of typhoon from the dynamic and thermal aspects.In the last 12 hours of the deterministic forecast,the experiment assimilating clear-sky MWHS-2 radiance is able to improve the 500 hPa circulation simulation with stronger southwest steering flow,which finally reduces the error of typhoon track forecast.