2008年初瞬变涡在中高纬阻高异常中的作用分析

Analysis on the Effect of the Transient Eddy on Ural Blocking High in 2008

2008年1月中旬到2月上旬,我国南方地区发生了历史罕见的、大范围的严重冰冻雨雪天气,中高纬大气环流异常尤其是乌拉尔阻塞高压(下称乌阻)异常发展、维持是非常重要的原因之一。为了探究中高纬阻塞高压(阻高)稳定维持的内在物理机制,以2008年初中高纬的一次阻塞过程为例,利用NCEP逐日再分析资料,从瞬变涡对平均经向、纬向气流的强迫作用、瞬变涡的动量输送以及瞬变涡的热量输送等方面分析和讨论了瞬变涡在中高纬阻高发展维持过程中所起的作用。结果表明,瞬变涡通过对平均流的强迫作用来加强阻高周围的反气旋气流。阻高区域内纬向气流的平均动能不断地转化成瞬变涡动能,而阻高北侧西风气流区域内瞬变涡动能则不断地向纬向气流的平均动能转化,这使得西风急流得以维持,有利于阻高的维持和发展。阻高区域内具有较强的瞬变涡热量输送,使得该区域内的温度梯度强度减弱,这在一定程度上又导致了平均西风气流的减弱,有利于阻高的发展和维持。

A rarely and large-scale snowfall event with severe freezing occurred in the southern China,during the period from the middle ten days of January to the first ten days of February 2008,whose key causes are the anomalous atmospheric circulation in the mid-higher latitudes,especially the unusual development and maintenance of the Ural blocking high（hereafter UBH）.The effect of the transient eddy on the development and maintenance of a blocking high（BH） in the mid-higher latitudes is analyzed,taking the blocking process in 2008 as an example,based on the following three factors：（1） the transient eddy forcing on the meridional and zonal flows,（2） the transient eddy momentum transport,and（3） the transient eddy heat transport.The results show that the transient eddy strengthens,via forcing the mean flow,the anticyclonic currents surrounding the BH,and thus favour the development and maintenance of the BH.On the other hand,despite the continuous conversion of the mean kinetic energy of the zonal flow change into the transient eddy kinetic energy in the BH area,the continuous conversion of the mean kinetic energy of the zonal flow change into the transient eddy kinetic energy in the westerly area in the northern part of the BH to cause the maintenance of the westerly jet and,as a result,leads the BH to develop and maintain.In addition,the strong transient eddy heat transport in the area causes the temperature gradient in this area to weaken,which is,to some extent,able to lead the mean westerly flow to weaken and thus favour the development and maintenance of the BH.