GRAPES_GFS在东亚地区中期预报技巧极端下降现象的初步研究

A PRELIMINARY STUDY ON THE MEDIUM-RANGE FORECAST BUSTS OF GRAPES_GFS IN EAST ASIA

关键词:  中期预报技巧极端下降  GRAPES_GFS  距平相关系数  东亚预报误差

Key words:  medium-range forecast bust  GRAPES_GFS  ACC  forecast errors in East Asia

摘要:

利用2016年4月1日—2018年12月31日GRAPES_GFS模式的业务预报数据，将GRAPES_GFS模式在东亚地区144小时预报500 hPa高度场的距平相关系数小于0.4，均方根误差大于60 gpm的事件定义为模式在东亚地区的中期预报技巧极端下降事件，据此标准筛选出29个个例进行了研究。结果表明，GRAPES_GFS在东亚地区中期预报技巧极端下降事件的高发期主要在春秋季，春季和秋季分别占比31.03%、41.38%，预报技巧极端下降事件通常表现在对于东亚大槽、西伯利亚槽脊、副热带高压的预报失败，四个季节合成的模式偏差均与该季节影响东亚地区主要天气系统的预报偏差大有关系。进一步通过典型个例的研究表明，东亚地区中期预报技巧极端下降事件的误差来源在不同季节表现出不同特征。冬夏季的预报偏差来源于高纬极区，多与模式在极区存在较大预报误差关联；春秋季的预报偏差主要来源于上游地区，与模式在东亚上游预报误差向下游的传播有关，未能合理预报台风活动也是预报偏差来源之一。

Abstract:

The “forecast bust” of GRAPES_GFS is investigated over the East Asian area by using the operational forecast data of GRAPES_GFS model during the period from April 1, 2016 to December 31, 2018. The “forecast bust” is defined as the cases when the area-averaged root mean square error (RMSE) of the day-6 forecast of geopotential height at 500hPa exceeds 60 gpm, as well as the its anomaly correlation being less than 0.4. According to this definition, the 29 cases have been identified. Of which, the high incidence of GRAPES_GFS medium-range forecast busts in East Asia is mainly in spring and autumn, with spring and autumn accounting for 31.03% and 41.38%, respectively. The medium-range forecast busts of GRAPES_GFS model in East Asia is usually manifested in the failure of the forecast of the East Asian trough, the Siberian trough, the Siberian ridge and the subtropical high. The composite of forecast errors in the four seasons are closely related to the forecast errors of the main weather systems that affect East Asia during that season. Further case studies have shown that the sources of errors in the forecast busts in East Asia exhibit different characteristics in different seasons. The forecast errors in winter and summer come from high latitude polar region, which are mostly related to the large forecast errors of the model in the polar region; the forecast errors in spring and autumn mainly come from the upstream areas, which are related to the propagation of the model's upstream forecast errors to the downstream. In addition, the failure of the model to properly forecast typhoon activity is also one of the sources of forecast errors.