基于全球模式检验结果的海上台风初始场重建技术研制和应用

Development and Application of Typhoon Initial Field Reconstruction Technology over Sea Based on Evaluation Results of Global Models

ECMWF和GFS全球模式对2016—2019年影响浙江台风路径和强度预报的评估结果表明:ECMWF模式对路径预报总体优于GFS模式,而GFS模式对强度预报更具优势。为提高台风数值预报性能,基于该评估结论提出了一种业务可行的台风初始化方案。该方案基于ECMWF和GFS分析场及洋面台风观测资料,利用台风涡旋分离技术,将从GFS分析场分离得到的涡旋场进行重定位和最大风速调整,然后与从ECMWF分析场中分离得到的大尺度环境场重新叠加融合,实现了台风初始场重建。针对近年14个影响浙江台风个例,应用台风初始场重建技术的中尺度数值天气预报业务模式的回报试验表明:经过初始场重建后,模式预报结果能兼顾ECMWF模式的路径预报优势和GFS模式的强度预报优势,有效改进了台风路径和强度预报性能。新方法的路径预报绝对误差较GFS模式驱动的中尺度模式预报结果减少21 km,标准差降低26.6 km;新方法的强度预报绝对误差较ECMWF模式驱动的中尺度模式预报结果减少1.7 m·s^(-1),标准差降低2.3 m·s^(-1)。对超强台风利奇马典型个例的进一步分析得到,初始场重建技术对大气环流特征和台风暖心结构模拟均有较好的修正能力。

The evaluation results of ECMWF and GFS on the track and strength forecasts of typhoons affecting Zhejiang from 2016 to 2019 show that ECMWF is better than GFS for track forecasting,and GFS has more advantages for strength forecasting.On this basis,the paper proposes a feasible typhoon initialization scheme to improve the performance of typhoon forecasting skill.Based on ECMWF and GFS analysis fields and oceanic typhoon observation data,as well as typhoon vortex separation,the vortex field is obtained by separating the GFS analysis field,and after vortex relocation and maximum wind speed adjustment procedure,it is superimposed with the large-scale environmental field separated from the ECMWF analysis field,realizing the reconstruction of typhoon initial field.For 14 typhoons affecting Zhejiang in recent years,the hindcasting results of the mesoscale numerical weather forecast model which uses the new reconstruction scheme demonstrate that the new scheme gives full play to the ECMWF’s advantages in track forecasting and GFS’s advantages in strength forecasting,improving the forecast accuracy of typhoon track and strength effectively.The absolute error of track forecast is reduced by 21 km and the standard deviation by 26.6 km compared with the prediction of the GFS-driven mesoscale model.Compared with the forecast result of the ECMWF driven mesoscale model,the absolute error of strength forecast is reduced by 1.7 m·s^(-1) and the standard deviation by 2.3 m·s^(-1).The analysis of the typical case of Super Typhoon Lekima(2019)further indicates that the initial field reconstruction technology has a better forecasting ability for atmospheric circulation characteristics and typhoon’s warm core structure.