海南岛春季一次特大暴雨过程的成因及其预报偏差

Analysis of the cause and forecast deviation of a heavy rain in spring in Hainan Island

2022年4月30日夜间至2022年5月1日白天,海南岛东半部地区出现了历史同期罕见的局地200 mm以上的特大暴雨,其中,琼海和万宁有6个自动站的日降雨量达到300 mm以上,超过历史同期极值,主客观预报均比实况偏弱50~100 mm.本文利用地面观测资料、卫星、雷达、ERA5再分析资料(0.25°×0.25°)对此次暴雨的环流背景、中尺度对流系统触发和发展机制进行了详细分析.结果表明,此次暴雨过程分为两个阶段,分别发生在冷空气影响前后,30日夜间海南岛东部地区大气可降水量和水汽通量呈现明显的异常特征,东北风向海南岛东岸喇叭口地形灌进时,辐合上升加强,同时,海岸线附近,由于海陆摩擦的差别,形成中尺度切变线,切变线上的中尺度对流系统自南向北移动,造成东部沿海地区强降水的发生.1日白天降水的主要原因是冷暖气流在海南岛东北部地区交汇,海南岛北部有东北—西南走向切变,东北急流带来南海北部的大量水汽输送,低层有强烈的垂直上升运动.数值模式对有无暴雨具有较好的可预报性,ECMWF模式预报的强降水中心量级偏小与其对低层风场和水汽通量预报偏差有关.

From the night of 30 April,2022 to the daytime of 1 May,2022,the eastern half of Hainan Island experienced a local torrential rain over 200 mm.The daily rainfall of 6 automatic stations in Qionghai and Wanning were more than 300 mm,which are more than the highset record of the corresponding historica data.The subjective and objective predictions were significantly weaker than the observation data by 50~100 mm.In the report,the ground observation data,satellite,radar and ERA5 reanalysis data(0.25°×0.25°) were used to analyze the circulation background of the rainstorm,the triggering and development mechanism of the mesoscale convective system and the possible causes of the forecast deviation.The results showed that the rainstorm process could be divided into two stages,which occurred before and after the arrival of the cold air.On the night of 30 April,2022,the atmospheric precipitable and water vapor flux in the eastern part of Hainan Island showed obvious abnormal characteristics.When the Northeast wind came into the bell mouth topography on the east bank of Hainan Island,due to the friction difference between land and sea,a mesoscale shear line was formed,and the mesoscale convection system on the shear line moved from South to North,which result in the occurrence of heavy rainfall in the eastern coastal area.The main reason for the precipitation on the daytime of 1May,2022 was that the cold and warm air flows met in the Northeast of Hainan Island.There was a NortheastSouthwest shear in the North of Hainan Island.The Northeast jet brought a large amount of water vapor transport from the North of the South China Sea,and there was a strong vertical upward movement in the lower layer.The numerical model has a good predictability for the occurrence of the heavy rain.The small magnitude of the heavy rainfall center predicted by ECMWF model was related to the prediction deviation of low-level wind field and water vapor flux.