高原低涡客观识别方法及其初步应用

Objective Identifying Method of Qinghai-Xizang Plateau Vortex Using NCEP/NCAR Reanalysis Dataset

利用2009年NCEP/NCAR再分析资料讨论了再分析资料在分析青藏高原(下称高原)低涡识别中的应用,利用天气学和计算几何学知识,根据高度场和风场资料定义了闭合低涡、面积、连续、区域、垂直结构及气旋性旋转等高原低涡的识别标准,讨论了高原低涡的客观识别方法;利用低涡中心位势高度值与环境高度场平均高度值定义了新的高原低涡强度指数;利用最大移动距离判定和最小环境气流—低涡移动矢量差相结合的连接高原低涡连续移动路径。结果共识别出53个低涡,对低涡的源地、季节差异、强度、持续时间和路径进行了分析;对客观识别结果与2009年高原低涡年鉴进行了对比,除了环流转换季节4月和10月外,两者的低涡个数较为一致;客观识别结果的低涡生成位置较年鉴结果偏西,低涡活动路径更为细致。该识别方法可以实现客观、定量地分析高原低涡的活动特征;与以往高原低涡天气图的分析方法相比,客观识别方法可以减轻分析高原低涡的工作量。

The application of reanalysis data to identify plateau vortex over the Qinghai-Xizang Plateau using NCEP/NCAR reanalysis data in 2009 is discussed. Based on geopotential height field and wind field, the plateau vortex recognition standard is defined by requirements including closing vortex, acreage, continuity, location, vertical structure and cyclonic shear. The plateau vortex objective identifying method is discussed using the knowledge of meteorology and computational-geometry. A new intensity index of the plateau vortex is defined as the difference between the minimum geopotential height of the central plateau vortex and the average geopotential height of the environment flow of plateau vortex. The maximum motion distance and minimum vector difference between environment flow vector and plateau vortex motion vector are combined to join the plateau vortex continuous motion tracks. 53 plateau vortexes are identified in all. The features of initial location, seasonal distribution, intensity, life period, and motion tracks of plateau vortex are analyzed using the recognition dataset. The objective identifying （OI） result is compared with the dataset of ‘The Yearbook of Plateau Vortex and Shear Lines in 2009’（YB）. The comparison shows that OI′s plateau vortex track is consistent with YB′s except April and October which are the switching seasons; Part of the plateau vortex positions has major differences？more than 10 longitude/latitude. The OI′s plateau vortexgenesis location is more western than the YB′s, and the OI＇s plateau vortex track shows more meticulous details than the YB′s. The objective identifying method can analyze the plateau vortex activity objectively and quantitatively and also can reduce the burden for the plateau vortex analysis work from the artificial reading weather maps work of analyzing plateau vortex.