淮河流域典型旱涝年夏季大气低频振荡特征

Features of atmospheric low-frequency oscillation in serious flood and drought summers occurred over Huaihe River Basin

分析了淮河流域典型旱涝年夏季逐日降水的主要周期,涝年30 d以上低频振荡的方差贡献大于旱年。500 hPa高度场30～60 d低频振荡方差贡献大值区与持续正高度异常对应,涝年欧亚中高纬度的低频振荡方差贡献大于旱年,而副热带、热带地区方差贡献小于旱年。旱年夏季,南半球澳大利亚高压较涝年弱,北半球低纬度地区850 hPa低频西风和印尼附近低频越赤道气明显强于涝年。涝年中国大陆沿海的低频反气旋位置较旱年偏南,江南、华南为低频西南气流控制。涝年ITCZ位于菲律宾附近,位置也比旱年偏南。旱、涝年夏季,200 hPa伊朗高原均为低频反气旋,南亚高压呈伊朗高压模态。旱年夏季,欧亚中纬度的低频反气旋导致南亚高压活动偏北,而涝年夏季南亚高压活动偏南。

Covariance of 30-90 d oscillation is more obvious in flood summers than droughts by filtering daily rainfall through band-pass filter.Persistent anomalies of geopotential height are closely related to the areas,where low-frequency oscillation is stronger.Extratropical low-frequency oscillation covariance over Eurasia is stronger in flood summers,while it＇s weaker in tropic and subtropics.The more vigorous low-frequency west wind at 850 hPa prevails at low latitude NH in drought summers,and cross-equatorial flow over Indonesia around 105 °E is also strengthened.In flood summers,the low-frequency anticyclone is located in Taiwan Island,more south than that in drought summers,which leads to vigorous SW flow over south China so as to significantly affect the rainfall in Huaihe River basin.Low-frequency anticyclones are also found in Iran plateau at 200 hPa both in flood and drought summers.Due to exratropical low-frequency anticyclone over Eurasia,the south Asian high acts more frequently in the north of the continent in drought summers.