1981-2010年江淮地区持续性强降水低频特征分析

基于1981-2010年国家气象信息中心提供的全国756站逐日降水数据建立江淮地区降水指数,选取6-7月江淮地区持续性强降水事件共26例,利用集合经验模态分解方法分析江淮地区的持续性强降水的低频性质。结果表明江淮流域夏季降水呈现随振荡周期增大方差贡献减小的趋势,根据江淮流域夏季持续性强降水的低频性质可以分成三类,其中10-30天低频振荡主导的事件占全部事件的50%,其低频成分的贡献达45.9%；10-30天和30-60天低频振荡共同主导的事件占全部事件的34.6%,10-30天低频成分的贡献达39.9%,30-60天低频成分的贡献达20.9%。在10-30天低频尺度上,事件发生前期自副高系统产生向极的波动能量的传播进而形成中纬度位势高度负异常,30-60天低频尺度上的位势高度异常稳定维持在利于持续性强降水发生的位相,为10-30天关键低频系统的形成提供一个有利的背景场,两个时间尺度上的低频活动在事件发生期间索相。在低频尺度上导致江淮地区持续性强降水的主要原因是位于南海至菲律宾北部的低频反气旋系统携带大量暖湿水汽沿西南东北向不断输送至江淮地区,低频反气旋与中纬度低频气旋系统在江淮地区强烈辐合导致持续性强降水的发生。

Properties of the Low Frequency Oscillations of Persistent Heavy Precipitation in the Yangtze-Huai River Valley during 1981-2010

Based on the daily precipitation data of 1981-2010 from observations collected at 756 stations in China are provided by China Meteorological Information Center, a precipitation index (PRE index) are defined. In total there are 26 persistent extreme precipitation events in the Yangtze-Huai River valley in June and July. The Ensemble Empirical Mode Decomposition (EEMD) method is applied to investigate oscillation properties of the persistent heavy precipitation events in the Yangtze-Huai River valley. Results indicate that the variance contribution of summer precipitation in the Yangtze-Huai River valley shows a decreasing trend with the increase of oscillation period. According to the low frequency characteristics of persistent heavy rainfall, the selected events can be divided into three categories. The events dominated by 10-30 days oscillation account for 50% of the total events, the contribution of low frequency component is 45.9%. The events dominated by both 10-30 days and 30-60 days oscillation account for 34.6% of the total events, the contribution of 10-30 days and 30-60 days oscillation account for 39.9% and 20.9%. On the 10-30 days low frequency scales, a mid-latitude negative height anomaly is formed when the wave energy originated from the subtropical high dispersive northward. The anomaly systems on 30-60 days scale stabilize at the positive phase, which is conducive to the occurrence of persistent heavy rainfall. Low frequency activities on this two time scales occur phase-locked during the event happen. On the low frequency scale, the anticyclone controlled by the subtropical high accompanied with warm moist airflow intersects with the cyclonic system and remained in the Yangtze-Huai River valley longer than three days, persistent heavy precipitation occur.