江淮梅雨区1960—2014年夏季极端降水变化特征及影响因素

Variation characteristics and influencing factors of extreme precipitation in the Meiyu area of Yangtze-Huai River Basin during 1960-2014

利用江淮梅雨区66个测站1960—2014年逐日降水数据和同期NCEP/NCAR再分析资料,基于多个极端降水指数,通过趋势分析、EOF分析和合成分析等手段,探究该区夏季极端降水事件的时空变化特征及影响因素。结果表明:(1)夏季极端降水指数以上升为主,显著上升区主要位于东部。(2)夏季极端降水指数第一特征向量呈全"+"分布形态,北部地区更强,第二特征向量呈"西北+东南-"分布形态;第一模态时间系数呈上升趋势,第二模态时间系数变化趋势不明显。(3)在强(弱)夏季极端降水典型年,西太平洋副热带高压位置偏西(东),中纬度地区表现出经(纬)向型环流分布特征,利于(不利于)江淮地区极端降水发生;同时,对流层中、低层上升运动增强(中层气流辐散增强),水汽通量增强、辐合(减弱、辐散),因此,梅雨区极端降水异常增强(减弱)。

Based on the daily precipitation data from 66 stations in the Meiyu area of Yangtze-Huai River Basin and the NCEP/NCAR reanalysis data from 1960 to 2014,several extreme precipitation indices were used to explore the spatial and temporal variation characteristics and influencing factors of regional summer extreme precipitation with the help of trend analysis,EOF analysis and composite analysis.The main results are as follows:(1)The summer extreme precipitation indices mainly show an upward trend,and the significant ascending zone is mainly located in the eastern part of the region.(2)The first eigenvector of these indices shows a uniform“+”distribution pattern but it’s stronger in the north area,and the second has a“positive in the northwest and negative in the southeast”distribution pattern.Temporal coefficient of the first mode shows an upward trend but the second temporal coefficient has no obvious trend.(3)In the typical years of strong(weak)summer extreme precipitation,the location of the Western Pacific Subtropical High extends westward(eastward),and the mid-latitude region shows the meridional(zonal)circulation characteristics,which is favorable(unfavorable)for the occurrence of the extreme precipitation in the Yangtze-Huai River region.Meanwhile,the intensity of the summer extreme precipitation in the Meiyu area is abnormally strengthened(weakened)when the ascending motion is enhanced in the middle and lower troposphere(when the airflow divergence in the middle troposphere is enhanced),and the water vapor flux is enhanced and convergent(weakened and divergent),leading to more(less)extreme precipitation.