Impact Of ATOVS Microwave Data Assimilation On Typhoon"Megi"(2016) Forecasting

In this paper,the typhoon "Megi"(2016)is selected as the research object.Based on the WRF model and the WRF-3DVAR assimilation system,the FNL reanalysis data is used as the initial and boundary conditions,direct assimilation experiments were performed on ATOVS microwave data(AMSUA and MHS).Five groups of assimilation experiments are designed to discuss the impact of assimilation on two aspects of the path and intensity prediction before the typhoon landing and the precipitation forecast after landing.Using the methods of average deviation,root mean square error,correlation coefficient and TS score,the simulation results are analyzed.In order to find the mechanism how the microwave data assimilation influence the typhoon path,intensity and precipitation,the change and adjustment of the basic meteorological elements of the initial field and the assimilation increment of each main meteorological field are discussed in this paper.The simulation results of the 60 h before the typhoon landing show that for the simulation of the typhoon path,A15(only AMSUA data on NOAA15 was assimilated)has the best assimilation effect,and M18(only assimilated the MHS data on NOAA18)is also effective within 0~30 hours.For the simulation of the lowest pressure,the simulated intensity of each test is generally weak,and the sudden change of typhoon intensity could not be simulated.All the assimilation tests except M18 are superior to the control test,and A15 has the best assimilation effect.For the simulation of maximum wind speed,the A15 performs well.The maximum increment of the initial field temperature,humidity,zonal wind and meridional wind in five assimilation tests mainly occur above the upper level of 500 hPa.Satellite data assimilation affects the large-scale circulation situation such as 500 hPa geopotential height,500 hPa wind and 200 hPa wind by adjusting the basic elements such as temperature and humidity and wind field,effectively improving the movement path of typhoon.There is also a good correspondence between the change of warming heart structure and typhoon intensity.The simulation results of precipitation after typhoon landing shows that the root mean square error of the assimilation tests of the A15 and M18 decreased by 23.23% and 13.8%,respectively.The results of TS scores shows that each assimilation experiment improves the24-hour precipitation forecast to varying degrees.Among them,A15 and M18 had the best assimilation results,and all the predictions of four precipitation levels were improved.A15 and M18 are more effective for small rainfall forecasting,and combined assimilation satellite platforms or sensors can improve the forecast of severe precipitation over 200 mm.The700hPa relative humidity,water vapor flux and 200 hPa divergence field have a consistent relationship with the change of precipitation.This indicates that satellite data assimilation improves the precipitation forecast by affecting the adjustment of water vapor conditions and vertical motion conditions.AMSUA assimilation on NOAA15 has a good simulation effect on typhoon path,strength and precipitation.