西藏拉萨市一次强对流天气过程中尺度及预报失误分析

Mesoscale Analysis and Forecast Error of a Severe Convective Weather Process in Lhasa,Tibet

利用常规气象观测资料、区域自动站资料、FY—4卫星云图资料、拉萨多普勒雷达资料,对2020年7月9日20∶00发生在拉萨及其周边的异地强对流天气的环流背景、动力和热力条件、中尺度系统和雷达特征进行了分析,并进行数值预报检验以及预报失误原因分析。结果表明:(1)夏季预报中,需要多考虑较有利的大尺度环流背景下激发的中小尺度系统的发生发展;(2)此次拉萨强降水为高空槽东移过程中携带的冷空气与低纬度低压前的西南暖湿气流在拉萨上空交绥的过程中激发了中尺度对流系统,中尺度对流系统的强度和移动路径以及地面辐合线是预报此次强降水、局部大雨落区的关键因素;(3)数值预报产品虽已成为天气预报日常业务中的重要参考资料,但西藏强降水多是由中小尺度系统以及地形因素引起的,因此预报能力有较大误差;(4)多普勒雷达组合反射率以及卫星云图的发展变化对西藏短时强降水系统的发生发展提供重要参考;(5)对于强降水的预报,数值预报很难报出落区和量级;(6)低空强烈的水汽辐合是暴雨发生的主要原因,暴雨发生前的不稳定能量为暴雨的发生提供有利的热力条件。拉萨位于高原东坡(河谷地带),有地形的阻挡和加热作用,是大气不稳定能量聚集地。

Using conventional meteorological observation data,regional automatic station data,FY-4 satellite cloud image data,and Lhasa Doppler radar data to determine the circulation background of the strong convective weather in and around Lhasa at 20:00 on July 9,2020.Dynamic and thermal conditions,mesoscale systems,and radar characteristics are analyzed,numerical forecast verification,and reasons for forecast errors are analyzed.The results show:(1)In summer forecasts,more favorable large-scale circulation background excitations need to be considered The occurrence and development of small and medium-scale systems in Lhasa.(2)The cold air carried during the eastward movement of the Lhasa trough and the warm southwestern warm air currents before low latitude and low pressure in Lhasa stimulated the mesoscale The convective system,the strength and movement path of the mesoscale convective system,and the ground convergence line are the key factors for forecasting the heavy precipitation and local heavy rain.(3)Although numerical forecast products have become important references in the daily business of weather forecasting However,the heavy rainfall in Tibet is mostly caused by small and medium-scale systems and topographical factors,so the forecasting ability has large errors.(4)The development and changes of Doppler radar combined reflectivity and satellite cloud images affect the system of shortterm heavy rainfall in Tibet.The occurrence and development provide an important reference.(5)For the forecast of heavy rainfall,it is difficult to report the falling area and magnitude of the numerical forecast.(6)The strong water vapor convergence at low altitude is the main reason for the occurrence of heavy rainfall,and the unstable energy before the occurrence of heavy rainfall It provides favorable thermal conditions for the occurrence of heavy rains.Lhasa is located on the east slope of the plateau(river valley).The terrain is blocked and heated,and is a place where unstable energy is concentrated in the atmosphere.