Characteristics and causes of the extreme precipitation anomaly in Lake Poyang area

Abstract

鄱阳湖区域4-7月极端降水总量存在显著的2-4年周期变化,且鄱阳湖4-7月极端降水总量的变率存在比较显著的增加趋势.1998年6月鄱阳湖地区极端降水总量异常偏多,而2001年6月异常偏少,仅为1998年的13.5%左右.通过分析大气环流场、水汽输送等方面的差异,发现1998年6月500hPa高度场上乌拉尔山高脊和鄂霍次克海高脊发展,贝加尔湖大槽加深,为鄱阳湖极端降水的产生提供了有利的环流背景,850hPa高度场上西太平洋副高增强,使得副高西北侧的西南气流增强北上与由贝加尔湖低槽引导南下的偏北风气流交绥于长江流域,并且增强的西南气流把大量的水汽带到鄱阳湖地区,同时对应高层南亚高压增强,从而使得鄱阳湖地区有充足的水汽来源并产生强烈的上升运动.而2001年6月500hPa高度场上中高纬地区环流经向发展,850hPa西太平洋副高位置相对偏东,水汽不易到达鄱阳湖地区,且贝加尔湖低槽减弱,使得北方冷空气不易到达鄱阳湖区域,同时对应高层南亚高压偏弱偏西,从而使得鄱阳湖地区上升运动减弱.;The extreme precipitation (EP) amount from April to July in Lake Poyang area exhibits significant quasi-periodic oscillations of 2-4 years, and its variance has remarkable ascendant trend. June EP amount in Lake Poyang area was abundant in 1998, while it decreased sharply in 2001, which only accounted for 13.5% of annual precipitation in 1998. Tlirough analyzing the difference of atmospheric circulation and moisture transport between the two periods, the results show that the developed high ridge near the Ural mountains and Okhotsk Sea and the stronger trough around Lake Baikal have offered a favorable circulation background for the EP in Lake Poyang area in June, 1998. Because of the strengthened Western Pacific subtropical high(WPSH), the stronger southwesterly in the northwest part of WPSH transported plentifiil moisture to the area, and it converged with the northerly around the Yangtze River valley. Meanwhile, the South Asia high was reinforced at upper layers, which led to strong ascending motion in Lake Poyang area. While the eastward shifted WPSH and ihe meridional developed circulation over the middle and high latitude at 500hPa reduced the moisture transport in Lake Poyang anea significantly in June, 2001. Moreover, the weakened north cold air from the trough around Lake Baikal was difficult to reach Lake Poyang area, and the weakened South Asia high decreased the ascending motion in the area.