梅雨锋结构特征及与锋上涡旋扰动关系的诊断分析

利用1999年6月下旬持续性梅雨锋降水过程的模拟结果以及野外实验的加密资料，对这次梅雨锋过程进行诊断分析， 发现梅雨锋主；要表现为中层锋面，强度比边界层锋强，低涡沿中层锋面南缘移动。中层锋强的演变对两类低涡（西南涡和局地涡）发展的影响程度不同。对于东移明显的西南涡，梅雨锋强度的加强比低涡提早6小时以上。而对于长江中游的局地涡，锋面最强与低涡最强出现的时间却比较接近。梅雨锋中层锋面发展最强的位置与低涡发展最强的位置在东西方向上基本重合，基本在同一经度上。因此，低涡暴雨扰动加强发展区的北侧正是前期持续锋生所在，并且锋生的位置在东西方向上基本不随时间发生位移。当低涡移经该地时，低涡强度最强， 随后低涡东移并且强度减弱，锋面大值带也减弱并随低涡向东传播。

The Structure of Meiyu Front and the Relationship between the Front and the Vortex Disturbance along It

In early summer,with the seasonal adjustment of atmosphere general circulation, especially with the north jumping of the western Pacific subtropical high and East Asian monsoon,the rainy season is coming in the middle-lower reaches of the Yangtze River.This was called Meiyu season.Meiyu front is a macro-scale system,and it is not uniform.It results in sustained rainfall.The nonuniformity of Meiyu front is closely related to macro-scale system and mesoscale convective system.Meiyu front and vortex along front influence each other.In order to improve the forecast accuracy,Mesoscale model MM5,intensive observation data,TBB(the cloud top black body temperature) data are used in studying the relationship between the nonuniformity of Meiyu front structure and vortex disturbance during the last ten days of June 1999.There were five vortexes during 0000 UTC 22 June 1999 to 0000 UTC 1 July 1999,and two of them were south west vortexes, and the others were local vortexes.The main results of diagnostic analysis are as follows.Middle level front is the main form of Meiyu front,and it is stronger than boundary front.Middle level front is higher than the vorticity center of vortex.Low vortex moves along the south edge of middle level front.There is a good relationship between the middle level front and the vortexes along it.The evolvement of middle level front has different effects on the southwest vortex and the local vortex.As for the southwest vortex,the development of vortex and Meiyu front is not at the same time.The frontogenesis appears about 6 hours or more earlier than the development of vortex.As for the local vortex, the development of vortex and Meiyu front is almost at the same time.The middle level front can foreshow the evolution of vortex,especially the south west vortex.So studying the development of middle level front would have a good implication for the two types of vortexes forecast.The location where the middle level front is the strongest is near to the north of that where the low vortex is the strongest.The two places are almost at the same longitude.So the front develops most just to the north of location where the low vortex develops later.Before the low vortex develops most,middle level front goes on developing at the same place with almost no displacement,and the vortex will be the strongest in the same place in the future.When the low vortex passes,the middle level front propagates eastward and weakens.This character has a good implication for forecasting the development of vortex.When middle level front goes on developing in a place,and there is a vortex in the west of this place,then the vortex will be the strongest when it moves to this place.The vortex will become weak after it passes.