2007年夏季中国大陆85°E以东的异常天气与气候——中国科学院大气物理研究所2007年汛期降水预测的总结

对中国科学院大气物理研究所2007年的夏季(6~8月)降水预测进行检验,结果表明,3月底的预测与实况有一定差异,6月的预测有所改进。简要讨论了2007年夏季的主要降水过程及其成因。2007年夏季华南、长江中下游和淮河流域先后出现梅雨锋强降水,6月中旬和8月中旬出现两次Rossby波列的下游发展效应,引起陕甘宁一次强降水以及加强了圣帕台风引起的强降水。7月上中旬出现高压脊发展后,下游小低槽强烈斜压发展过程引起淮河出现致洪暴雨以及济南暴雨灾害。7月中下旬,由于阻高南侧的3次高空槽切断过程,造成重庆地区以及山西和豫西的暴雨灾害。在东亚季风区,夏季大气季节内振荡很显著,而且对降水的时空分布有重要影响。由于短期气候预测对夏季风季节内变化的预测还是一个难点,这给汛期降水的可预报性带来了限制。

The Anomalous Weather and Climate of China in the Summer 2007——Verification of Seasonal Climate Predictions of Institute of Atmospheric Physics/Chinese Academy of Sciences

The prediction of summer rainfall from June to August 2007 by Institute of Atmospheric Physics/Chinese Academy of Sciences is tested.The prediction made in March turned out to deviate from the actual observation by certain degree;while this was improved in the later prediction in June.During the summer 2007,there were Mei-Yu frontal heavy rainfalls appearing successively along the Pearl River,the middle and lower reaches of the Yangtze River,and the Huaihe River valley,the subtropical anticyclone in the West Pacific extended westward and northward for six times.In July there were three cases of cut-off processes of the upper troughs in the inner land of China,leading to severe rainstorms there.In the normal years the cut-off processes are a rare occurrence in this area.Also,in July there were downstream baroclinic development processes in eastern China,bringing about disastrous rainstorms in the Huaihe River valley and severe convective in Shangdong Province.There were two Rossby wave trains in Eurasia in June and August,causing high impact weather in Shaanxi,Gansu and Ningxia Provinces as well as in South China.In recent years,the Thorpex program,which aims at the improvement of the accuracy of 1 to 14-day high impact forecast,suggests that the downstream development of the Rossby wave trains and the process of the downstream baroclinic development are producers of high impact weather.In this sense,in China the summer of 2007 is the year of the frequent occurrence of high impact weather,it is the year of anomalous weather and climate in China.It is found that in the eastern Asia summer monsoon region,the main feature of monsoon circulation is characterized by the marked intraseasonal oscillation(ISO) of the monsoon rainfall,which account for the 50%-70% of the interannual variability of the seasonal rainfall.Owing to the strong influence of the ISO,the predictability of seasonal monsoon rainfall predictions is limited.In the preparation of the seasonal rainfall predictions in China,how to take into account of the effects of ISO is a challenge to the forecasts.