“东方之星”翻沉事件强对流天气分析及数值模拟

摘要

2015年6月1日21:32(北京时)左右,“东方之星”号客轮由南京开往重庆途中,行至湖北省荆州市监利县长江大马洲水道时遭遇狂风暴雨天气而翻沉.经调查分析,此次事故是由一次突发罕见的飑线天气伴随的下击暴流袭击所致.使用ARPS模式,同化常规资料及监利县周边4部雷达资料,综合多种观测分析飑线伴随下击暴流过程中系统结构及发展变化特点,结果表明:降水质点的拖曳和下沉气流的共同作用是强对流活动发生发展和下击暴流产生的重要原因,低层干燥、中层湿润的不稳定层结有利于动能向下传输及地面大风的生成.数值模拟表明:地面水平风场大值区、近地面水平和垂直风向风速变化、10 min累积降水量大值中心和组合反射率因子高值区走向呈一致的带状分布,与观测对应良好.受下击暴流直接影响,事故点附近的雷雨大风强度陡增,近地面出现狭窄的阵风锋,风切变明显;事故点附近主要受到超过10m·s-1的下沉气流和超过18 m·s-1的强烈偏西风共同影响,降水中心分钟降水量超过10 mm.%At about 2132 BT 1 June 2015,"Oriental Star" cruise from Nanjing for Chongqing suffers severe stormy weather when sailing in the Yangtze River near Jianli County,resulting in 442 people killed.The investigation team finds that the occurrence of the catastrophic accident is caused by a sudden downburst of squall line weather.Using ARPS (the Advanced Regional Prediction System) model and assimilation of conventional data and four-radar data in the surrounding area,the severe weather process is simulated.Combined with the high-resolution radar observation,the structure and strength of the squall line are analyzed synthetically.The atmosphere of dry ambient at low level and humid ambient at middle level is favorable for the occurrence of convective weather phenomena.Radar observations show that the squall line convective system is northeast-southwest direction,and moves fast to southeast,the life duration is about 6 hours,and the squall line transit lasts about an hour.During the evolution of the squall line,convections developed to their strongest at the intensifying stage,when the strong convection region reached its maximum.At its mature stage,gust front appears in front of ground thunderstorms,and the horizontal scale of the squall line system reaches the upper limit.The instability of the stratification and the flat terrain of the Jianghan Plain are important causes for the strong convective activity and the downburst phenomenon.The numerical simulation shows that the high-speed wind area above the ground,the position of instantaneous maximum speed of horizontal and vertical wind,cumulative rainfall maximum center,the composite reflectivity high value area of 200 m resolution show a zonal distribution to uniform,which coordinates with the time and spatial distribution of the accident.Influenced by the direct impact of the down burst,intensity of thunderstorm near the accident point increases rapidly,and a narrow gust wind appears near the ground where wind shear increased significantly.Ship wreck is affected by above 10 m · s-1 downdraft and above 18 m · s-1 strong westerly wind from 2132 BT to 2134 BT.The precipitation intensity begins to increase at 2131 BT,and the center of heavy precipitation is located just above the accident spot from 2131 BT to 2135 BT,with a maximum precipitation of more than 10 mm per minute.A gust wind makes great contribution to the transportation of momentum from the middle and low levels to the land surface,accompanied by raindrops of drag and the sinking air flow,enhancing the speed of the wind further.