浙江省梅雨锋强降水的锋生及环流特征分析

Analysis of Frontogenesis and Circulation Characteristics of the Meiyu Front with Heavy Precipitation in Zhejiang Province

为了研究浙中西(浙江省中部和西部)梅雨锋强降水的锋生及环流特征,以2016年6月15日一次典型梅雨为代表,采用ERA-INTERIM(0.25°×0.25°)再分析资料、FY-2E卫星云顶亮温和雷达资料,运用风场分解、合成分析等方法对锋生与强降水的对应关系及环流结构进行分析。结果表明:此次典型梅雨处于有利的天气尺度背景下,强降水区与中低层锋生区有较好对应。锋区维持时,强降水区伴随中层倾斜锋生和形变锋生;锋区南压时,强降水区伴随中层倾斜锋生和低层水平锋生。低层梅雨锋北侧为超地转偏西气流,南侧为非地转东南气流,它们分别影响了北侧非平衡偏北气流和南侧平衡西南气流的发展,从而影响锋生系统。在锋区存在低层地转偏差辐合、高层辐散的上升运动,形成次级环流上升支,锋后反之。此外,锋前低空纬向风为次地转,而锋后低空纬向风为超地转,高空纬向风为次地转,这进一步促进了次级环流的发展。合成场中,在200 hPa西风槽槽后及槽前分别存在西北气流和西南气流显著增强区;在700 hPa浙北(浙江北部)地区存在东北气流显著增强区。合成锋生各分解项的水平及垂直分布与典型个例较类似。低层锋生主要由散度项贡献,形变项次之,倾斜项则起负作用;中层锋生主要由倾斜项贡献,形变项次之;高层锋消主要由倾斜项贡献。

This paper analyzes the frontogenetic and circulation characteristics in central and western Zhejiang Province as represented by a typical Meiyu process on 15 June 2016. Based on ERA-INTERIM(0.25°×0.25°) reanalysis data, FY-2 E TBB(Black Body Temperature) data, and radar data, the relationship between frontogenesis and heavy precipitation,and the characteristics of circulation, were analyzed by means of wind decomposition and composite analysis. Results indicated that the typical Mei-yu was under a favorable synoptic-scale background, and the heavy precipitation area was closely related to the low-to-mid-level frontogenesis. When the frontal zone persisted, it was accompanied by mid-level deformation and tilting frontogenesis. When the frontal zone shifted southward, it was accompanied by mid-level tilting frontogenesis and low-level horizontal frontogenesis. The super-geostrophic westerly airflow on the north side of the lowlevel Mei-yu front and the strong southeast ageostrophic airflow on the south side affected the unbalanced northerly airflow on the north side and the balanced southwesterly airflow on the south side, thus affecting frontal development. In the frontal zone, upward motion, which formed the ascending branch of the secondary circulation, was caused by lowlevel geostrophic deviation convergence and upper-level divergence. The contrary was found in the post-frontal area.Additionally, in the pre-frontal area, the low-level zonal wind was sub-geostrophic, while in the post-frontal area, the lowlevel zonal wind was super-geostrophic, and the upper-level zonal wind was sub-geostrophic. Thus further enhanced the secondary circulation. After composite, there was an area of significant enhancement of the northwesterly and southwesterly airflow behind and in the frontal trough at 200 hPa. In addition, there was a significant northeasterly wind variation area over northern Zhejiang Province at 700 hPa. Horizontal and vertical distribution of the decomposition items were similar between the composite and typical cases. Low-level frontogenesis was mainly contributed to by the divergence term, followed by the deformation term, while the tilting term had a negative contribution. Mid-level frontogenesis was mainly contributed to by the tilting term, followed by the deformation term. Upper-level frontolysis was mainly contributed to by the tilting term.