1979—2016年四川盆地低涡的气候特征分析

利用6 h一次、水平分辨率为0.25°×0.25°的ERA-Interim再分析资料,对1979—2016年生成于四川盆地的西南涡的发生和发展进行统计分析。结果表明：四川盆地低涡集中生成于盆地内;在6月生成最多,7月发展最强;按移动情况不同可将其分为5类：东移型、东北移型、东南移型、西移型和少动型;东移型、东南移型、少动型低涡生成个数的峰值在6月,东北移型和西移型低涡生成个数的峰值在7月。夏季5类长生命史四川盆地低涡的结构和降水合成场表明：从发展强度看,东北移型最强,少动型最弱。从成熟期垂直结构看,除西移型外,低涡均随高度向西北或向西倾斜,在对流层低层为冷性结构,中层为暖性结构;东移型、东北移型、西移型低涡的正涡度区在垂直方向伸展更高;除东南移型、西移型低涡的强上升区与其中心重合外,其余类型位于其中心东侧。从降水特征看,除西移型外,其余类型低涡的降水中心均位于其移动路径东侧或东北侧,其中东北移型低涡成熟期6 h累计降水量最大。四川盆地低涡的强上升区、相对湿度大值区、位于对流层低层和中层的辐合辐散中心与降水所在位置有很好的对应关系,各物理量场相互作用共同促进低涡发展。

Climatological characteristics of Sichuan Basin vortex during 1979-2016

Using the 6 h,0.25°×0.25°ERA-Interim reanalysis data during 1979-2016,the vortexes generated from Sichuan Basin are detected and analyzed.The results show that the generation of Sichuan Basin vortex is mainly concentrated in Sichuan Basin.It is the most frequent in June and strongest in July.Sichuan Basin vortexes can be divided into 5 categories according to its migration,including eastward-migrating type,northeastwardmigrating type,southeastward-migrating type,westward-migrating type and stationary type.The generation of eastward-migrating,southeastward-migrating,and stationary types of Sichuan Basin vortexes peaks in June,while that of other types peaks in July.Structure and precipitation of long-lived Sichuan Basin vortexes in summer are discussed through a composite analysis.The northeast-migrating type is the strongest and the stationary type is the weakest.Concerning the structure in the maturation stage,except the westward-migrating type,vortexes of other categories are cold at lower layers and warm at middle layers,with a northwest or west tilt.Eastward-migrating,northeastward-migrating and westward-migrating types can reach higher levels than others.The strongest ascent motion of southeastward-migrating and westward-migrating types coincides with the vorticity center,while it is located at the east side of the vortex center for others.For precipitation,except for the westward-migrating type,the maximum 6 h-precipitation appears at the east or northeast side of the vortex center.And 6 h-precipitation of northeastward-migrating type is the strongest among all types.For the Sichuan Basin vortex,there is a good correspondence among the strong ascent motion,the high relative humidity,the convergence and divergence centers at the middle and lower troposphere,and the location of precipitation.The interaction of various physical quantity fields jointly promotes the development of the vortex.