2011年华西秋雨特征及其成因分析

Analysis of Autumn Rainfall Characteristics and Its Causes in West China in 2011

2011年入秋以来,华西北部、黄淮、华北南部等地秋雨明显,具有局地降水强度大、持续时间长的特点,灾害影响重。形成此次秋雨异常事件的主要原因是受LaNi?a事件的影响,赤道中东太平洋地区海温异常偏低,在西北太平洋到我国沿海一带形成"异常气旋—反气旋对"的环流特征。在这样的环流配置下,低纬地区经孟加拉湾北上的西南气流强盛,与源自西太平洋偏强的东南气流汇合,将来自海洋的暖湿空气源源不断地向北输送,源自西太平洋的偏东水汽输送异常明显,对降水异常偏多起主要作用;在中高纬度地区,贝加尔湖以东地区维持异常低槽区,易引导冷空气持续频繁南下影响我国华西北部及其以北地区。同时,副高主体偏北少动使得冷暖气流在华西北部至黄淮一带交汇并稳定维持,从而形成较大范围的持续性降水。

Since the autumn of 2011, there has been obvious precipitation in northern areas of West China, Huang-Huai and southern areas of North China, which is characterized by high local intensity, long duration and serious disasters. The formation of this precipitation is mainly due to the SST of the middle and east Pacific Ocean abnormally lower, which was effected by the La Nia events and results in anomaly cyclone and anticyclone gyre circulation pattern in the Northwest Pacific and offshore region. Under such conditions, southwest airflow which moves northward along the Bay of Bengal, keeps strong and joins southeast airflow from the Western Pacific, thus warm and moist air from the ocean is continuously transported northwards. The eastern water vapor transport from the western Pacific is significantly obvious and mainly contributes to the significantly more pricipitation. In the meantine, abnormal trough maintains to the East of Lake Baikal, which guides the cold air frequently to the north of West China and its northern areas. The main subtropical high, located abnormally north and moving little, results in the cold and warm air converge and maintains from the northern part of the West China to the Huang-Huai area, causing the continuous precipitation.