Impact of assimilating FY-3C MWHS2 data in the RMAPS-ST forecast system on its rainfall forecasts

Abstract

In order to evaluate the impact of assimilating FY-3C satellite Microwave Humidity Sounder (MWHS2) data on rainfall forecasts in the new-generation Rapid-refresh Multi-scale Analysis and Prediction System–Short Term (RMAPS-ST) operational system, which is developed by the Institute of Urban Meteorology of the China Meteorological Administration, four experiments were carried out in this study: (i) Coldstart (no observations assimilated); (ii) CON (assimilation of conventional observations); (iii) FY3 (assimilation of FY-3C MWHS2 only); and (iv) FY3+CON (simultaneous assimilation of FY-3C MWHS2 and conventional observations). A precipitation process that took place in central-eastern China during 4–6 June 2019 was selected as a case study. When the authors assimilated the FY-3C MWHS2 data in the RMAPS-ST operational system, data quality control and bias correction were performed so that the O-B (observation minus background) values of the five humidity channels of MWHS2 became closer to a normal distribution, and the data basically satisfied the unbiased assumption. The results showed that, in this case, the predictions of both precipitation location and intensity were improved in the FY3+CON experiment compared with the other three experiments. Meanwhile, the prediction of atmospheric parameters for the mesoscale field was also improved, and the RMSE of the specific humidity forecast at the 850–400 hPa height was reduced. This study implies that FY-3C MWHS2 data can be successfully assimilated in a regional numerical model and has the potential to improve the forecasting of rainfall.摘要 中层水汽初值的误差是数值预报, 尤其是短期预报不确定性的重要来源. 星载微波湿度计资料能很好地弥补常规资料的不足, 同化微波湿度计资料对改善对流层中高层的水汽初始场精度有着重要意义. 本研究基于新一代快速更新多尺度资料分析和预报系统短期数值预报系统 (RMAPS-ST), 选取 2019 年6月 4–6 日中国华中地区降水过程开展了 FY-3C MWHS2 资料同化对于此次降水预报的影响评估. 研究开展了4组试验: 冷启动试验, 控制试验, 同化 FY-3C MWHS 试验, 同时同化常规观测和 FY-3C MWHS 试验. 结果表明:经质量控制及偏差订正之后 FY-3C MWHS2 各通道 O-B 明显趋于正态分布, 同化 FY-3C MWHS 资料后, 对此次降水过程降水落区和强度的预报均优于控制试验和冷启动试验, 同时对于环境场的预报也有改善.