2007年淮河强降水时期低频环流特征

The characteristics of low frequency circulation during the heavy rainfall season over the Huaihe river basin in 2007

利用NCEP/NCAR再分析资料以及中国气象台站降水资料,研究了2007年夏季淮河流域强降水的低频振荡及其环流特征。结果表明,2007年夏季淮河流域强降水低频振荡的主要周期是10 25天。淮河流域降水强弱与对应低频周期存在联系,降水主要发生在低频周期的正位相时期,而在负位相时期结束或明显减弱。降水的低频变化一方面与副热带高压和南亚高压的低频变化有关,另一方面还受到中高纬度冷空气低频变化的影响。在低频周期的峰值位相,对流层高层出现的低频反气旋使南亚高压偏东,脊线偏北,并有利于西太平洋副热带高压向更西、更北的方向发展,整个对流层垂直方向上有低频的上升运动。中高纬地区出现大片正位势涡度,冷空气的低频活动显著偏强,南下侵入到中国淮河流域的冷空气较多,形成有利于淮河流域强降水的环流场。相反,在低频周期的谷值位相,对流层高层出现的低频气旋使南亚高压偏西,脊线偏南,不利于西太平洋副热带高压向更西、更北的方向发展,整个对流层垂直方向上有低频的下沉运动。高纬度冷空气的低频活动偏弱,南下侵入到中国淮河流域的冷空气也较少,最终形成不利于淮河流域强降水的环流场。

The NCEP/NCAR reanalysis data and observed daily precipitation data were used to investigate the intraseasonal variability of heavy rainfall and circulation characteristics in Summer 2007.The results show that the intraseasonal variation of precipitation in summer 2007 over the Huaihe river basin was mainly controlled by the 10 - 25 days oscillation.The precipitation intensity in the Huaihe river basin was related to the corresponding low-frequency periods.The mostly rainfalls happened in positive phase of the low-frequency periods and ended or weakened evidently in negative phase.The precipitation low-frequency variability in the Huaihe river basin was related with the low-frequency evolvement of the western Pacific subtropical high and South Asia high and,also with the low-frequency variation of the cold airs over the mid-high latitudes.In the peak phase of the low-frequency periods,there is a low-frequency anticyclone in the higher troposphere,which caused the South Asia high to shift eastward its ridge line extending northward and favoured the westward and northward development of the western Pacific subtropical high developed,with low-frequency upward current existing in the whole troposphere.At the same time,the isentropic analysis indicates that positive potential vorticity appeared in the high-latitude areas.And the cold airs that reached southward the Huaihe river basin were more active than the normal.A favorable circulation environment for heavy rainfall over the Huaihe river basin was then formed.On the other hand,in the vale phase of the low-frequency periods,there is a low-frequency cyclone in the higher troposphere,caused the South Asia high to shift westward with its ridge line extending southward.The western Pacific subtropical high developed then eastward and southward with the low-frequency sinking motion existing throughout the troposphere with the negative potential vorticity appeared in the high-latitude areas and the cold airs reached the Huaihe river basin being less active than the normal.An unfavorable circulation environment for heavy rainfall over the Huaihe river basin was formed ultimately.