1999—2008年夏季华北冷涡的异常特征

利用1999—2008年5—8月中国160站月平均气温资料、每日2次的MICAPS资料及每日4次的NCEP 1°×1°资料，通过定义一个夏季华北冷涡强度指数(NCCVI)，研究了夏季华北冷涡异常年西太平洋副高、东亚季风、高空急流及低层垂直运动的异常特征。结果表明：夏季NCCVI异常强年500 hPa上贝加尔湖地区有气旋性环流发展,从贝加尔湖至我国华北地区为一显著的高空槽所控制,冷空气较活跃并随槽后引导气流扩散南下影响华北地区。对流层各层偏暖湿，200 hPa上高空急流偏强，700 hPa上高纬冷涡后部偏北气流加强，低纬偏南气流加强，冷暖空气在华北交汇，华北和东北地区低层上升运动发展。同期副热带高压偏强，位置略偏南；东亚夏季风偏强, 加强了水汽输送。夏季NCCVI异常弱年相反。

Anomalous Features of Summer Cold Vortex over North China from 1999 to 2008

Utilizing the monthly average temperature data of 160 stations,MICAPS data(two times per day) and NCEP 1°×1°data(four times per day) of May to August from 1999 to 2008,the conceptual model of severe convection associated with the cold vortex is devised,and the anomalies of the subtropical high pressure,East Asian monsoon,high-altitude jet,and low-level vertical motion are studied in the anomalous years of the cold vortex in summer.The results indicate that in the strong anomalous years of summer NCCVI(Nouth China Cold Vortex Index),there is a cyclonic circulation developed at 500 hPa over Lake Baikal,an upper trough from Lake Baikal to North China,and more active cold air;North China is affected by the south-spreading steering flow after the trough.Various levels of the troposphere are warmer and wetter;the high-altitude jet in 200 hPa is stronger;the northerly air stream in the rear cold vortex at 700 hPa strengthens at high latitudes,and southerly air stream strengthens at low latitudes;the cold air and warm air converges in North China;ascending motion at lower levels develops over North China and North East.Over the same period,the subtropical high pressure is stronger and more southern;East Asian summer monsoon is stronger,which increases the transport of water vapor.In the weak anomalous years of summer NCCVI,these are on the contrary.