华南前汛期一次锋前暖区暴雨成因及中尺度对流系统分析. (Esperanto)

The evolution of three mesoscale convective systems (MCS), i. e., MCS-A, MCS-B, MCS-C, experienced multiple division and reorganization, resulting in a heavy rainfall in the warm sector ahead of fronts in Southern China on 27 March 2020, which sustained for more than 15 hours. The synoptic background, organization modes and initiation conditions of MCS are analyzed by using surface automatic meteorological stations data, Doppler weather radar data, ERA-Interim reanalysis data and mesoscale CMAGD model data. The results are shown as follows. (1) Favorable configuration and stable circulation systems, including a 500 hPa upper-level trough, a 200 hPa westerly jet and a frontal trough are important reasons for long-term maintenance of the warm-sector heavy rainfall. The low-level jet provides conditional instability and convective available potential energy for the generation and development of convection. (2) The convection in key region 1 from Hezhou to Huaiji was triggered on the ground with the decrease of the level of free convection and the reduction of CIN energy. The interaction between wind speed convergence at the height of 1500 m and a cool pool in key region 2 80 km away from key region 1 resulted in the convection. (3) MCS-A and MCS-B are modulated into forward and backward propagation in key region 1, while MCS-C is modulated into backward propagation in key region 2. The convective cells of all three MCSs form echo "train band effects". In addition, both MCS-B and MCS-C form several short and parallel convective rainbands in a nearly N-S direction triggering eastward "train band effects". MCS-A and MCS-B split again into short and parallel convective rainbands in a nearly NE-SW direction triggering southeastward "train band effects". (4) The warm and humid southwesterly flow on the left side of the meso - β - scale secondary circulation is lifted, releasing latent heat and triggering convection. The interaction of the cold outflow resulting from the drag effect of heavy precipitation formed a downdraft below 850 hPa and a warm inflow on the west side near the surface was conductive to new convection, which was the development mechanism of the backward propagation. (5) Forward propagation was caused by the convergence between the cold pool outflow, which was formed on the ground after the genesis of upstream MCSs, and the warm moist flow. [ABSTRACT FROM AUTHOR]

2020 年3 月27 日华南地区发生一次典型的锋前暖区暴雨过程, 过程持续超过15 h, 出现中尺度对流 系统MCS-A、MCS-B 与MCS-C 并产生多次分裂与重组。利用地面自动站数据、多普勒天气雷达资料、 ECMWF-ERA5 地面和高空再分析场资料, 结合中尺度CMA-GD模式对此次暖区暴雨过程环流形势与中尺度 对流系统组织特征和触发条件等方面进行分析。结果表明：（1）高低空环流包括500 hPa 高空槽、200 hPa 西风 急流与锋前低槽等系统的有利配置且稳定少动是暖区暴雨长时间维持的重要原因。持续维持的低空急流为对 流发生发展提供了有利的条件性不稳定和对流有效位能。（2）伴随自由对流高度降低与CIN抑制能量减小, 贺 州至怀集一带的关键区域1 处对流在地面得以触发, 而距离1 处南向约80 km的关键区域2 中1 500 m高度处 风速辐合与冷池作用使得对流发生。（3）MCS-A与MCS-B在关键区域1 处触发, 呈现前向与后向传播, MCS-C 在关键区域2 处触发后以后向传播为主。此外, MCS-B与MCS-C表现为多条平行排列的南北向短雨带并产生 向东移动的"列车带效应", 而MCS-A与MCS-B则表现为多次分裂与重组后形成向东南移动的"列车带效应"。 （4）中β 尺度次级环流的上升支抬升西南暖湿气流, 使其倾斜上升凝结潜热释放, 造成后向传播对流系统的发 生发展。同时由于强降水拖曳作用, 850 hPa 以下转下沉气流造成一定厚度的冷池后与暖湿入流叠加, 触发新 对流单体, 也影响后向传播。（5）上游MCSs 发生后在地面形成冷池出流, 与暖湿气流辐合抬升, 造成前端对流 触发. [ABSTRACT FROM AUTHOR]

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