2008年1月南方冰雪过程的可预报性问题分析

Predictability of Snow Storm and Freezing Rain Disaster in Southern China in January 2008

主要根据欧洲中期天气预报中心（ECMWF）的中期预报资料,东京气候中心（TCC）的集成预测系统,给出1～2周、月及季度预报图,从短期、中期和长期3个时间尺度,分析和讨论2008年1月中旬至2月初我国南方发生的严重低温雨雪冰冻灾害性天气过程的可预报性问题。对最严重的一次冰雪天气过程（1月25～29日）,ECMWF提前1～7 d十分成功地预报出亚洲中高纬60～100°E地区为阻塞高压控制,在其南侧里海以东地区维持切断低压,可以追踪从切断低压中分裂的一个气旋性扰动沿青藏高原向东移入我国华南上空的静止锋上,对于盘踞在东亚地区的冷高压楔也能够很好地预报出来。TCC的中期以及延伸期预报（提前1～2周）,较好预报了80°E附近的阻塞高压和南支西风带中高原上空的低压槽,但对里海附近的切断低压以及中国东海岸的高压脊没有预报出来;同时,对中国南方的强降水也没有预报出来。TCC对于2007/2008年冬季和2008年1月平均的500 hPa大气环流和中国南方降水异常的预测结果不好。月、季预报的可预报性比较差,这可能是由于数值模式本身的缺陷,或是由于目前对极端异常气候事件的长期预报水平本身就很低。从中期预报讲,2008年1月11日～2月1日中国南方严重暴雪、冻雨灾害可在5～10 d前预报出来。要作2008年1月我国南方低温雨雪冰冻天气这类持续性异常气象灾害事件的季度或月预报有很多困难。

Based on the operational medium-range and extended range forecasts by ECMWF,and Tokyo Climate Center（TCC）,the quality of the forecast for the snow storm and freezing rain disaster in Southern China from 25-29 January 2008 is analyzed.It is found that the ECMWF medium-range forecast was quite successful in predicting the process of a cyclonic vorticity system breaking off from the cut-off low near the Caspian Sea and moving to downstream along the Tibetan Plateau to the quasi-stationary front over China,and also successful in predicting the large-scale flow associated with the severe snow and freezing rain for 25-29 January and the sea level high pressure wedge in eastern China.In addition,the extended range forecast provided by TCC was successful in predicting the 500 hPa large-scale circulation pattern over Asia for the period 26 January to 1 February 2008,but failed to the precipitation during the same period.As to the prediction of the January snow and ice storm for more than one month and a season,the forecasts given by TCC and NCEP-CPS were not successful both in predicting the large-scale circulation and the precipitation for the snow storm and freezing rain disaster in Southern China in January 2008.The inconsistency between the forecasts and observations may be either due to the model errors or the existing low skill of predictability for this anomalous event.But for the medium and extended range forecast,the snow storm and freezing rain disaster in January 2008 can be predicted up to 5 days in advance.