珠三角北部一次暖区强降水过程中的地形作用

EFFECT OF TOPOGRAPHY ON A WARM-SECTOR HEAVY RAINFALL EVENT IN THE NORTHERN PEARL RIVER DELTA

关键词:  暖区暴雨  地形  珠三角北部

Key words:  warm-sector heavy rainfall  topography  northern Pearl River Delta

摘要:

基于ERA5再分析资料、广东省风廓线雷达、雷达拼图产品和实况观测数据，分析了2020年6月7日夜间—8日珠三角（珠江三角洲）北部暖区强降水过程中主雨带与南岭南部地形走势一致的原因，阐释地形对此次强降水的触发和维持作用。结果表明：（1） 此次过程发生在典型的暖区暴雨环流特征的背景下，主要影响系统为对流层中层弱短波槽扰动、低空急流和边界层急流脉冲等；（2） 雷达回波表现为团状结构，多以对流单体形态生消，伴随明显的“列车效应”现象，但3个不同发展阶段内回波的持续时间、强度，以及触发地、传播和移动方向等均存在差异；（3） 由于边界层西南（偏南）风增强和地形作用，新的对流单体在珠江口附近和珠三角西北侧被触发，同时由于南岭南侧地形对边界层暖湿气流的阻挡和拦截等作用，使得气流在珠三角北部形成明显的辐合抬升，造成该区域内对流单体移速减慢和汇聚，增强了降水强度；（4） 强降水长时间的持续与海陆热力差异、冷池和边界层暖湿气流增强等引起的地面露点锋和中尺度辐合线有关。露点锋为强降水的发展和维持提供了热力不稳定条件，地面辐合线加强了对流层底层气流的辐合抬升，进一步增强了强降水区的降水强度。研究结果有助于认识珠三角北部暖区强降水过程中地形的重要作用，为今后该区域防灾减灾提供气象理论支撑。

Abstract:

Based on the ERA5 reanalysis data, data from wind profile radar and radar mosaic products of Guangdong Province, as well as observational data, this paper analyzed the heavy rainfall process in the warm sector over northern Pearl River Delta during June 7-8, 2020 in Guangdong, found that the heavy rainfall belt is distributed in the direction of northwest-southeast along the southern edge of the Nanling, and explained the triggering and maintaining effect of topography on the heavy rainfall. The results show that: (1) The process takes place under the background of typical warm-sector rainstorm circulation, and the main influencing systems are the weak short-wave trough disturbance in the middle troposphere, low-level jet, and boundary layer jet pulse. (2) Accompanied by obvious “train effect”, the radar echo shows a cluster structure, mostly in the form of convective cell. However, the echo duration, intensity, trigger location, and propagation and moving direction are different in three development stages. (3) Due to topography and the enhancement of southwest (southerly) wind in the boundary layer, new convective cells are triggered near the Pearl River Estuary and the northwest side of the Pearl River Delta. Meanwhile, due to the blocking and interception by topography on the warm and moist air flow in the boundary layer on the south side of the Nanling Mountains, the air flow forms obvious convergence and uplift, and thus the precipitation intensity is enhanced. (4) The long-term persistence of heavy rainfall is related to the surface dew point front and mesoscale convergence line caused by the difference of land and sea heat, cold pool and the enhancement of warm and moist flow in the boundary layer. The dew point front provides thermal instability conditions for the development and maintenance of heavy rainfall. The surface convergence line strengthens the convergence and uplift of airflow in the lower troposphere, and further enhances the precipitation intensity in the strong rainfall area. The results can facilitate our understanding of the important role of topography in the process of heavy rainfall in the warm sector over the northern Pearl River Delta and provide theoretical support for disaster prevention and mitigation in the future.