重庆夏季旱涝急转与大气环流异常的联系

利用1961—2012年期间重庆的逐月降水和同期NCEP/NCAR再分析资料、NOAA的海温、国家气候中心提供的126项环流指数等资料,结合长周期旱涝急转指数,分析了重庆旱涝急转的时间演变特征及其与同期和前期大气环流异常的联系.结果表明:重庆夏季旱涝急转事件有阶段连续性和间歇性并存的特点,年际差异大,涝转旱强度通常比旱转涝强度偏强.旱转涝年的旱期与涝转旱年的涝期比较,其环流特征为西太平洋副高偏西、偏强、面积偏大,低层垂直下沉运动较强,来自南海及西太平洋的水汽输送较弱,重庆易处于水汽输送辐散区,易少雨偏旱.而旱转涝年的涝期对比于涝转旱年的旱期来看,其环流特征为欧洲西岸的槽偏强,极涡偏弱,西太平洋副高偏强、偏西,低层垂直上升运动较强,来自南海及西太平洋的水汽输送较强,重庆易位于水汽输送辐合区,易多雨偏涝.西太平洋副高的季节内振荡的异常是重庆旱涝急转的主要原因.前期3月和4月的PDO和西风漂流区海温指数可以作为预测重庆夏季旱涝急转的一个先兆信号,前期3月和4月的PDO偏强(弱)、西风漂流区指数偏弱(强)时,重庆夏季可能易发生旱转涝(涝转旱)事件.

The relationship between summer drought-flood abrupt alternation in Chongqing and the anomalous of atmospheric circulation

On the basis of studying the monthly rainfall data and the NCEP/NCAR reanalysis data,the sea temperature data provided by NOAA and 126 circulation indexes provided by the National Climate Center (NCC) that combined with a long-cycle drought-flood abrupt alternation index,the relationships between timely changing characteristics of Chongqings drought-flood abrupt alternation and the atmospheric circulation anomalies during the same period and prophase have been analyzed in this paper.The results are as followsthe summer drought-flood abrupt alternation events in Chongqing have the characteristics of both phase continuity and intermittent coexist,displaying huge annual differences,and the flood-to-drought situation is worse than the drought-to-flood situation.By comparing the drought period of the drought- to-flood years with the flood period of the flood-to-drought years,weve found that the western Pacific subtropical high is abnormally westward,also stronger and wider than before,which will lead to a stronger lower vertical sinking movement and the lack of water vapor transportation from the South China Sea and the western Pacific Ocean,so Chongqing is likely be at the water vapor transporting divergence area,which will lead to little rainfall and will result in drought.By comparing the flood period of the drought- to-flood years with the drought period of the flood-to-drought years,weve also found the trough of west coast of Europe is stronger and the polar vortex is weaker,the western Pacific subtropical high is abnormally westward and stronger,which will lead to a stronger lower vertical sinking movement and a strong water vapor transportation from the south China sea and the western Pacific Ocean,then Chongqing is likely to be at the water vapor transporting divergence area,which results in vast precipitation and floods.The seasonal abnormal oscillation of western Pacific subtropical high might be the major reason for the drought-flood abrupt alternation in Chongqing.The early PDO in March and April together with the sea temperature index of the west wind drift area can be used as a warning signal for Chongqings drought-flood abrupt alternation prediction,which will lead to drought-flood abrupt alternation events when the early PDO in March and April is stronger and the sea temperature index of the west wind drift area is weaker.