春季影响江淮地区的天气尺度气旋活动与同期降水的联系

本文基于1979~2013年ERA-Interim逐日4次的850 hPa位势高度场资料，利用基于最外围闭合等值线的气旋区客观识别方法得到春季影响江淮地区的二维气旋集，依据水平尺度划分了天气尺度气旋并分析该区域气旋强度的时空分布特征以及气旋活动与站点降水异常的关系，结果表明:天气尺度气旋活动与江淮地区降水异常、强降水事件发生频次均存在显著的正相关关系。气旋活动指数高-低年份差值分析发现，随着气旋活动指数增强，东北亚地区对流层中上层增温并伴随异常高压中心出现，促使其南部南北经向温度梯度以及高空西风急流偏弱。这有利于江淮区域北部异常正涡度平流输入，同时江淮地区对流层低层形成横槽型环流，江淮区域南部及其上游地区对流层中下层出现异常西南气流，有利于江淮区域涡度增大，相应的低空辐合、高空辐散垂直结构，为天气尺度气旋发展与维持提供了有利的动力抬升条件。横槽型异常环流配置有利于江淮区域南部的西南暖湿气流和北部的异常西向/西北向水汽输入和堆积，导致区域云量以及降水异常的增多。

Simultaneous Relationship between Precipitation and Activities of Springtime Synoptic Scale Affecting Cyclone over the Yangtzi-Huaihe River Valleys

Based on 850-hPa geopotential height field at 6-hour intervals extracted from the ERA-Interim reanalysis data during 1979-2013, cyclones that affected over the Yangtzi-Huaihe River valleys (YHV) in the spring were detected by using the 2D cyclone area objective identification method, which can detect the outermost enclosed contour of the cyclone. The spatial-temporal characteristics of synoptic-scale cyclones and their relationship with regional precipitation anomalies in the spring over the YHV were investigated. The results show that the inter-annual variation of synoptic-scale cyclone activities displays a significant positive correlation with precipitation anomalies as well as the occurrence frequency of heavy precipitation over the YHV. A significant quasi-barotropic high-pressure center exists in northeastern Asia when the cyclone activity intensifies, which is mainly induced by the upper troposphere warming that weakens the meridional temperature gradient to the south of Japan. Such a circulation configuration is conducive to the decrease in the upper westerly jet and positive vorticity advection in the northern part of the YHV, which are accompanied by anomalous southwesterlies in the middle and lower troposphere in the south of YHV. The horizontal trough and cyclonic circulation anomalies in the YHV result in increased vorticity over this area. The associated low-level convergence and high-level divergence provide a favorable dynamic lifting condition for the development and maintenance of synoptic scale cyclone in the YHV. The abnormal circulation configuration of the lower level horizontal trough is favorable for the intensification of warm, moist southwesterly flow in South China and anomalous easterly/southeasterly flow in northern YHV, and thus leads to increases in regional cloud cover and precipitation anomalies.