Data Assimilation Of CFOSAT Scatterometer Wind Field And Its Application In Typhoon Forecast

Typhoon is one of the most serious natural disasters in China's coastal areas.China is invaded by about 7 typhoons every year.The severe weather and sea conditions caused by typhoons seriously damage the safety of people's lives and property in coastal areas.It is of great importance to accurately forecast the path and intensity of typhoons for improving disaster prevention and control ability.The key to improve the ability of numerical prediction is to construct better initial conditions to reflect the atmospheric and oceanic conditions at the initial moment.Data assimilation is an effective way to improve the initial field of the model by using observation data.The scarcity of conventional observation data under typhoon conditions often makes it difficult for typhoon data assimilation,on the contrary,satellite data provide a good data source for typhoon forecast.Launched in 2018,the CFOSAT satellite is equipped with a domestically developed scatterometer,which can provide wind field data with high accuracy and wide space coverage.In this paper,3DVAR method and WRF model were adopted to carry out the Experiments on CFOSAT scatterometer wind field data assimilation and numerical prediction of typhoon.13 typhoons passing over the East China Sea and South China Sea from 2019 to 2020 were selected to carry out the Experiments.The effects of the conventional observation data assimilation and CFOSAT wind field data assimilation on typhoon prediction are compared and analyzed.The Experimental results of "BAILU",a typhoon case with good coverage of wind field data at the initial time of typhoon forecast,show that the introduction of CFOSAT data has improved the initial conditions and typhoon forecasts: in comparison with no data assimilation,the mean absolute error(MAE)of typhoon path prediction and the mean absolute error of central minimum sea level pressure are reduced by about 20 km and3%,but the maximum wind speed is not significantly improved.After assimilating the CFOSAT wind field data,the forecast error of the typhoon path and intensity was further reduced in comparison with no data assimilation,the mean absolute error of typhoon track forecast was lowered about 30 km,the lowest pressure at the typhoon center was reduced about 7%,the mean absolute error of central maximum wind speed was reduced about 20%.The overall analysis of 13 typhoon forecast results from 2019 to 2020 shows that the assimilation of CFOSAT wind field data reduces the forecast error of typhoon path and intensity to a certain extent.By assimilating the conventional observation data,the mean error of the 13 typhoon paths was reduced by about 4km,while the central minimum sea level pressure and the central maximum wind speed were not significantly improved.After assimilating CFOSAT wind field data,the forecast error of the typhoon path and intensity was further reduced in comparison with no data assimilation,the mean absolute error of typhoon track was lowered about 15 km,the minimum sea level pressure at the typhoon center was reduced about 3.5%,the mean absolute error of central maximum wind speed was reduced about 11%.