2014年夏季长江流域降水季节内振荡的环流分析

Circulation Analysis of Intraseasonal Oscillation of Precipitation in the Yangtze River Valley in the Summer of 2014

基于台站降水观测数据和MERRA-2再分析资料,分析了2014年夏季我国长江流域降水的季节内振荡特征,并从位涡角度重点研究了与之相关的环流演变。结果表明:2014年夏季长江流域降水季节内变率以10~20d的准双周振荡为主。在降水准双周振荡的极端湿位相,受对流层高层随中纬度波列东传的正异常位涡和南亚高压东侧西南向传播的正异常位涡的共同影响,南亚高压呈“马鞍型”分布,在长江流域形成高空辐散环流;在对流层中低层,当中纬度波列的异常气旋向东南传播至长江流域以北时,西太平洋异常反气旋延伸至中国东南沿海,二者共同导致长江流域低空水汽辐合加强;在高、低层环流的共同作用下,长江流域持续性降水显著偏多,形成准双周振荡的极端湿位相;同时,长江以北高空位涡正异常导致其下方冷空气下沉,触发长江流域异常上升运动和南海地区异常下沉运动,该经向垂直环流圈的形成有利于长江流域正异常降水的维持。反之则形成极端干相位。

Based on the observation data of precipitation at the stations and the reanalysis data of MERRA-2,the intraseasonal oscillation of the summer rainfall over the Yangtze River Valley in the summer of 2014 were analyzed,and the related atmospheric circulation was studied from potential vorticity perspective.The analysis shows that the intraseasonal variablility of precipitation in the Yangtze River Valley in the summer of 2014 was regulated by the 10-20d quasi-biweekly oscillation.In the extreme wet phase,the South Asian High is in a saddle shape pattern,just due to the combined effects of the positive anomalous potential vortices propagating eastward along the mid-latitude waves in the upper troposphere and the positive anomalous potential vortices propagating southwest on the east side of the South Asian High,forming a high-altitude divergent circulation in the Yangtze River Valley;in the middle and lower troposphere,when the mid-latitude anomalous cyclones propagates southesast to the north of the Yangtze River Valley,the anomalous anticyclone in the western Pa-cific extends to the southeast coast of China,enhancing the low-level water vapor convergence of the Yangtze River Valley.Due to the co-evolution between the upper and lower troposphere,positive rainfall anomalies persisted over the Yangtze River Valley.Furthermore,the ascending cold air under the upper-tropospheric positive potential vortices anomaly in the north of the Yangtze River Valley forced the an-omalous ascending motions over the Yangtze River Valley and the anomalous ascending motions over the South China Sea.Such a meri-dional vertical circulation was favorable for the persistence of anomalous rainfall in the Yangtze River Valley.The opposite situation is for the extreme dry phase.