浙江夏季弱天气尺度强迫背景下午后局地热对流特征分析

CHARACTERISTICS OF LOCAL THERMAL CONVECTION IN SUMMER AFTERNOON UNDER WEAK SYNOPTIC-SCALE FORCING IN ZHEJIANG

关键词:  弱天气尺度强迫  局地热对流  地形  海拔高度  对流参数

Key words:  weak synoptic-scale forcing  localized thermal convection  terrain  altitude  convection parameters

摘要:

利用常规高空观测资料、浙江多普勒雷达产品、ERA5逐小时再分析资料(0.25 °×0.25 °)，统计分析了2015—2021年浙江夏季(6—8月)弱天气尺度强迫背景下午后局地热对流(根据移动速度分为移动型和少动型两类)的时空分布特征、生命周期特征、环境参数特征等。(1) 两类热对流触发频次相当，年际变化均较大，但年、月、日变化趋势基本一致，午后出现少动型局地热对流的可能性更大，而傍晚出现移动型局地热对流的可能性更大。(2) 局地热对流的触发与地形密切相关，对流高频区位于浙东沿海、浙西北、浙西南山区，浙中北平原和盆地均为低频区，热对流触发频次均随高度增加而减少，多触发于山脉及其附近的中低海拔处，中高海拔地区更容易触发少动型局地热对流。(3) 两类对流均在弱垂直风切变环境下即可触发，移动型单体更容易得到发展。

Abstract:

Based on high-altitude observational data, Zhejiang Doppler radar products, and ERA5 hourly reanalysis data (0.25 °×0.25 °), the present study analyzed the spatial and temporal distribution, life cycle, and environmental parameters of local thermal convection (classified into localized moving convection and localized anchoring convection according to moving speed) in the afternoon under the background of weak synoptic-scale forcing in summer (from June to August) in Zhejiang from 2015 to 2021. The results show that: (1) The triggering frequency of the two types of thermal convection is the same, and the interannual variation is large, but the annual, monthly and daily variation trends are basically the same. Localized anchoring convection easily occurs in the afternoon while localized moving convection easily occurs in the evening. (2) The triggering of local thermal convection is closely related to the terrain. The high-frequency area is located in the coastal areas of eastern, northwestern, and southwestern mountainous areas in Zhejiang while the low-frequency area is located in the plain and basin in central and northern Zhejiang. The triggering frequency of thermal convection decreases with the increase in height, which is mostly triggered at the middle and low altitudes in the mountains and nearby. It is easier to trigger localized anchoring convection in the mid- and high-altitude areas. (3) Both types of convection can be triggered in the environment of weak vertical wind shear, and localized moving convection is easier to develop.