Atmospheric Intraseasonal Oscillation and Summer Drougt/Flood over the Yangtze-Huaihe River Basin

Abstract

观测资料的分析极为清楚地表明,江淮流域的夏季降水有着极为明显的低频变化,周期为30-60d和近20d的振荡是其最基本的特征,尤其是在多雨的年份.对应江淮夏季多雨(涝)年和少雨(旱)年,大气环流的分析表明其大气季节内振荡(IS0)的形势有着显著的差异.例如在多雨(少雨)年,在长江以南的850hPa上为一个低频(IS0)反气旋(气旋)性环流控制,而中国北部和日本一带为气旋(反气旋)性环流,从而在江淮流域形成较强的低频辐合(辐散)气流;在200hPa的青藏高原上却为一个低频气旋(反气旋)性环流所控制.分析还表明,对应多雨年,在江淮流域有明显的由中高讳度向南传播和由低玮度向北传播的大气低频振荡的汇合情况;而对应于少雨年,由中高纬度向南传播的低频系统较不明显,在江淮流域低频系统的汇合也较为不清楚.;The low frequency feature of summer rainfall over the Jianghuai (Yangtze-Huaihe) Rivers Basin and the influence of atmospheric intraseasonal oscillation (ISO) are studied by using data analysis. The 20-70 day (30-60 day and near by 20 day) oscillation is a fundamental feature of summer rainfall in the Jianghuai Rivers basin, particularly in the flood years. The ISO has different patterns in summer for the severe flood years and the severe drought years over the Jianghuai Rivers Basin. At 200hPa over the Tibetan Plateau, there are such different circulation patterns of the ISO in the severe flood and drought years; a cyclonic circulation of the ISO locates over the Tibetan Plateau region in severe flood years but an anticyclonic circulation of the ISO locates over the Tibetan Plateau region in severe drought years. At 850hPa, an anticyclonic (cyclonic) circulation system of the ISO occurs over the areas to the south of the Yangtze River, the South China Sea and the Western Pacific regions and an ISO cyclonic (anticyclonic) circulation system over North China-Japan regions for severe flood (drought) years. The atmospheric ISO at 500hPa and 200hPa in the middle-high latitudes from Lake Baikal to the Sea of Okhotsk is strong (weak) for severe flood (drought) years. The ISO in the middle-high latitudes can propagate southwards and meets with the northward propagating ISO from the lower latitudes over the Jianghuai Rivers Basin in the severe flood years, but the southward propagation of the ISO is not clear in the severe drought years.