高原涡与西南涡相互作用引发四川暴雨的位涡诊断

Diagnostic Analysis of Potential Vorticity on a Heavy Rain in Sichuan Basin under Interaction between Plateau Vortex and Southwest Vortex

利用目动气象站逐时降水量资料和欧洲中期天气预报中心ERA-interim再分析资料,对2013年6月28日至7月2日一次高原低涡(高原涡)与西南低涡(西南涡)相互作用引发四川盆地暴雨的天气过程进行了位涡诊断分析。根据Hoskins位涡理论,对比分析了位涡、高度场、风场中低涡中心的位置差异,分别揭示并验证了高原涡、西南涡在移动过程中的强度变化。结果表明:在高原涡、西南涡形成阶段,位涡中心都位于高度场、风场低涡中心的西侧。高原涡在东移到高原东部的过程中,强度加强;进入四川盆地继续东移的过程中,强度减弱。当高原涡与西南涡实现垂直耦合后,高原涡的强度再次加强;高原涡与西南涡处于非耦合状态时,高原涡东侧的下沉气流将抑制盆地西南涡的发展;而当高原涡东移出高原与盆地西南涡垂直耦合后可激发西南涡加强,高原涡与西南涡垂直合并为一个深厚强涡。从位涡剖面的垂直方向上不仅清晰地反映高原涡与西南涡相互作用过程以及两涡的移动,还可以表示低涡中心强度的变化。等嫡位涡水平面上能较好地反映高原涡、西南涡的移动及演变情况,对强降水中心也有指示作用,可从水平方向显示两涡相互作用过程。

The potential vorticity is used to diagnose the interaction between the Plateau Vortex(PV) and the Southwest Vortex(SWV) during the period of 28 June to 2 July 2013.According to the Hoskins potential vorticity theory,analyzed the vortex,height field and wind field of low vortex center position difference,verify the PV and SWV's intensity of movement of the change.The results show that when the form of vortex,the vorticity center are located in the west side of low vortex center of height field and wind field.The PV spread eastward,the intensity of strengthening.When the PV into the Sichuan Basin,the intensity weakening.Before the interaction,with PV moving eastward the downdraft can inhibit the development the SWV.When the PV removed the Tibetan Plateau,the PV interacts with the development of SWV.The vertical cross-section of potential vorticity can reflects PV interaction process with SWV and their movements,but also can be used to indicate changes in the intensity of the cyclone center.Analyses of isentropic potential vorticity indicate that the horizontal isentropic can well reflect the PV and the SWV interaction process.