西南低涡活动特征的再分析

用1979—2012年每天4次,1°×1°的ERA-INTERIM再分析资料,从风场角度定义了闭合式气旋环流和规定了低涡移出路径的统计方法后,对西南低涡的活动特征进行了统计分析。结果表明:西南低涡平均每年生成个数为59个,偏多的年份为1980、1989、1992、1997和2009年,平均可达69个;偏少的年份为1981、1990、1996和2006年,平均仅有51个。低涡在春季生成的个数最多,夏季次之,秋、冬季最少。6月和3月生成的个数最多;5月次之,其中11月生成的个数最少。各季节移出型低涡的个数则是夏季最多,春季次之,秋季和冬季最少。就移出率而言,夏季达44.1%,春季为27.6%,秋季为22.6%,冬季仅为11.3%。春、秋、冬季基本为短生命史的低涡,而在夏季,生命史长的低涡所占的比例较高。34 a中夏季维持较长生命史的移出型低涡共有126个,分别向东北(最多)、正东、东南(最少)3个方向移动,除正东方向外,向东北和东南方向移动的低涡个数随年代际变化呈增加的趋势。

Characteristics reanalysis on Southwest vortex

Based on the ERA-INTERIM reanalysis data with 6 h time resolution and 1°×1° spatial resolution from 1979 to 2012, the characteristics of the Southwest vortex were statistically analyzed after defining the closed cyclone circulation and setting up the statistic method of the vortex removement routine according to wind field. Result showed that 59 Southwest vortexes generated annually. There were more Southwest vortexes with the average value 69 in 1980,1989,1992,1997 and 2009, while in 1981,1990,1996 and 2006 there were less with the average value 51.The vortex generated the most in spring, then in summer, and the least was in autumn and winter.The maximum of vortex generated in June and March, followed by May, and November had the least. The number of removing vortex fluctuated in each season. Removing rate in summer, spring, autumn and winter were 44.1%, 27.6%, 22.6% and 11.3%, respectively. The short-life vortex occured basically in spring, autumn and winter, while in summer, the long-life vortex had a higher occurring proportion. Among 126 removing vortexs with long-life occurred in summer during 34 years, more of them moved to northeast than to east and southeast. The number of removing vortex shifting to the northeast and southeast increased with decadal variability.