2009—2015年ECMWF热带气旋集合预报的检验及分析

Verification and Analysis on Tropical Cyclone Ensemble Forecast of European Centre for Medium-Range Weather Forecasts from 2009 to 2015

本文从四个方面检验分析了ECMWF 2009—2015年西北太平洋热带气旋集合平均预报性能。结果表明:集合预报对路径的预测能力逐年提高,对强度预报整体偏弱。随着热带气旋强度增强,集合预报对移速和移向的预测能力提高,而移向预报偏左、移速预报偏慢、强度预测偏弱的现象较明显。将影响热带气旋的引导气流分为偏强、中等、偏弱三类,引导气流偏弱时热带气旋移动偏慢,因此移向预报的不确定性大;而引导气流偏强时热带气旋移向明确,只是移速预报不稳定。进入南海的三类路径热带气旋,集合预报对西行、西北行两类的移速、移向预报效果较好,而西行后北折的预报较差,在热带气旋北折前,移向预报发散度很大,向北转折后移向趋于稳定,移速预报的误差相对较大。这几种情形的检验结果,在热带气旋集合预报的业务应用中值得注意。

The verification and analysis on tropical cyclone （TC） ensemble forecast of European Centre for Medium-Range Weather Forecasts （ECMWF） over western North Pacific in 2009--2015 are given from four aspects. The results show that the capability of ensemble forecast on TC tracks has been improving annually, but the intensity forecasting is always weak. The stronger the TCs are, the more accurate the ensemble forecasts of TC moving speed and moving direction are, though the forecasted speed is slow and the forecasted direction turning leftwards exists, whereas the forecasted intensity is weaker. On the other hand, the steering flow of TCs is classified into three grades. When the steering flow is weak, the TC moves slowly, and the direction forecasting is uncertain; when the steering flow is strong, the TC moving direction forecasting is reliable, but the speed forecasting is not good enough. As to the TCs over South China Sea classified according to three different types of tracks, the speed and direction ensemble forecas- ting errors would be small in westerly and northwesterly tracks, but would be large in westerly to north- erly tracks. For the TC with westerly to northerly tracks, the direction forecasting has large spread before turning northerly, while the moving direction would be stable after turning northerly.