Evaluation of the Forecast Performance for North Atlantic Oscillation Onset

Abstract

By utilizing operational forecast products from TIGGE (The International Grand Global Ensemble) during 2006 to 2015, the forecasting performances of the European Centre for Medium-Range Weather Forecasts (ECMWF), National Centers for Environmental Prediction (NCEP), Japan Meteorology Agency (JMA) and China Meteorological Administration (CMA) for the onset of North Atlantic Oscillation (NAO) events are assessed against daily NCEP–NCAR reanalysis data. Twenty-two positive NAO (NAO+) and nine negative NAO (NAO−) events are identified during this time period. For these NAO events, control forecasts, one member of the ensemble that utilizes the currently most proper estimate of the analysis field and the best description of the model physics, are able to predict their onsets three to five days in advance. Moreover, the failure proportion for the prediction of NAO− onset is higher than that for NAO+ onset, which indicates that NAO− onset is harder to forecast. Among these four operational centers, ECMWF has performs best in predicting NAO onset, followed by NCEP, JMA, and then CMA. p]The forecasting performance of the ensemble mean is also investigated. It is found that, compared with the control forecast, the ensemble mean does not improve the forecasting skill with respect to the onset time of NAO events. Therefore, a confident forecast of NAO onset can only be achieved three to five days in advance.

摘要

利用2006至2015年间的TIGGE数据集, 以逐日的NCEP-NCAR再分析资料作为标准, 检验了欧洲中期天气预报中心(ECMWF), 美国国家环境预报中心(NCEP), 日本气象厅(JMA)和中国气象局(CMA)对NAO事件发生的预报水平. 在研究的时段内, 共选取了22个NAO正位相(NAO+)事件和9个NAO负位相(NAO−)事件. 对于所选取的NAO事件, 控制预报可以提前3–5天预报出事件的发生. 另外, NAO−事件预报失败率高于NAO+事件, 说明NAO−事件的发生预报更加困难. 对于NAO发生的预报, ECMWF在四个业务中心里表现最好, 其次是NCEP, JMA和CMA. 此外还研究了集合平均的预报水平. 研究发现, 相比于控制预报, 集合平均并不能有效地提高NAO事件发生的预报时效. 因此, 对于NAO事件发生, 可靠的预报时效只有3–5天.