东亚梅雨系统的天气-气候学研究

利用NCEP/NCAR逐日再分析资料、上海观测站降水资料，对上海2020年超强梅雨特征及成因进行了分析，并对基于大气低频特征的延伸期预报效果进行了评估。结果表明：（1）2020年上海梅雨量为2000年以来最多。（2）受夏季赤道中东太平洋冷水位相和热带印度洋海温异常偏暖的影响，西北太平洋异常反气旋强盛且稳定少动，其西侧转向的水汽输送偏强加之中高纬地区Rossby波列的传播引起中低层天气系统（槽、脊等）的变化，引发冷空气活动，也对副高的北抬起到了抑制作用，造成梅雨期偏长，雨量偏多。（3）2020年梅雨期降水过程表现出明显的准双周振荡特征，4次强降水过程均对应低频降水的峰值。沿Rossby波低频活动通量方向移动的低频波列南下，并与低频反气旋对峙于长江流域，导致多轮强降水。基于大气低频特征研发的延伸期预报方法较为准确地预报出2020年上海入梅首场强降水过程。

Analysis of the characterlstics of 30-60 day low-frequency oscillation over Asia during 1998 SCSMEX

Using NCEP daily reanalysis and observation data, we analyzed the characteristics of the 2020 Meiyu in Shanghai and evaluated the effectiveness of the extended range forecast which is based on the atmospheric low-frequency characteristics. The results show that (1) the 2020 Meiyu in Shanghai was the most severe one since 2000. (2) The excessive precipitation during Meiyu is caused due to the influence by the cold phase of equatorial central-east Pacific and the anomalously warm SST of the tropical Indian Ocean in summer, the strong and stable anomalous anticyclone in the northwest Pacific Ocean and the abnormally strong water vapor transport from its western turn, and the frequent cold air transfer along the direction of wave-activity flux. (3) The precipitation events in the 2020 Meiyu show obvious quasi-biweekly oscillation characteristics, with all four strong precipitation events corresponding to the peaks of low-frequency precipitation. The extended range precipitation forecast method developed based on the low-frequency characteristics is more accurate in predicting the first strong precipitation event in the 2020 Meiyu season.