The effect of the East Asian jet stream on the freezing rain and snowstorm over southern China in early 2008 was investigated using the European Centre for Medium-Range Weather Forecasts (ECMWF) interim data and the precipitation data provided by the China Meteorological Administration.Possible reasons for the change of the jet stream during the event were studied.The variation of the vertical motion in the jet entrance region was caused by changes in the intensity and position of the jet stream,leading to the development of precipitation over southern China.In order to study the causes of changes in the jet stream during the event,the eddy kinetic energy equation was used in this study.The analysis suggests that the development of the jet stream was corresponding to the variation of the eddy kinetic energy.The eddy geopotential advection made an important contribution to the eddy kinetic energy.A small eddy kinetic energy center associated with weak wind fields was located to the north of the jet stream,and the eddy kinetic energy was transported via the eddy geopotential flux to the jet entrance region and converged there,leading to the intensification of the jet stream.%利用欧洲中期预报中心再分析数据和中国气象局提供的降水数据分析了2008年1月到2月初东亚急流对我国南方雨雪冰冻灾害的影响,并给出东亚急流变化可能的原因.东亚急流强度和位置的变化引起其入口区的垂直运动的变化,从而使得我国南方降雨的位置和强度发生改变.为了研究灾害发生期间东亚急流变化的原因,利用扰动动能方程分析了与东亚急流有关扰动动能以及方程各项的变化,结果表明:扰动动能的变化能够很好的表示东亚急流的变化;扰动位势平流对扰动动能的发展至关重要.东亚急流北部弱风区存在较小的扰动动能中心,位势适量矢量将这个中心的扰动动能输送到东亚急流的入口区并辐合,使得东亚急流增强.
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