河西走廊西部一次极端大风天气过程3次风速波动的动力条件分析

Analysis on Dynamic Condition of Three Wind Speed Fluctuation Events during An Extreme Gale Process in the West of the Hexi Corridor

利用自动气象站、高空探测和NCAR/NCEP再分析资料,对2017年5月13日河西走廊西部极端大风天气的影响系统、3次风速波动和动力条件等方面进行了分析。结果表明:在阻塞高压发展加强和冷涡的异常南压作用下,冷平流和动量下传是河西走廊西部持续大风形成的关键因素;第一次大风波动主要与地面变压风有关,动量下传在第二、三次大风波动中起重要作用;在高空急流入口区中心及左侧伴生的下沉运动能有效将高空动量下传到500 hPa,低层不稳定层结发展的动量交换作用和热力、动力条件下所产生的垂直运动使中低空动量下传至近地面;前倾槽所形成的涡度平流上负下正结构极有利于动量下传,垂直方向上涡度平流梯度越大、梯度大值中心越低,越容易引发河西走廊西部近地面极端大风。

Using the data of automatic weather stations,the conventional observation and NCAR/NCEP reanalysis data,the influence system configuration,the characteristics of three wind speed fluctuation and dynamic Condition have been analyzed,In order to provide experience for the prediction of gale in special terrain conditions in Western Hexi corridor.The main results are as follows:With the development and strengthening of blocking anticyclone and Cold vortex abnormal moving southward,cool advection and downward momentum transfer of high low altitude are the key factors for the formation of continued gale in the west of the Hexi Corridor;The first gale fluctuation is mainly related to the ground pressure-swing wind,and the momentum downward transmission plays an important role in the second and third gale fluctuations;The descending motion with convergent flow field at the center and left side of the upper jet stream exit region can effectively transmit the momentum of high altitude below 500 hPa,The momentum exchange in the development of unstable stratification and the vertical motion caused by the thermal and dynamic conditions in the lower layer make the momentum in the middle and lower levels move down to the near ground.During the transit of the high-level trough,the configuration of the negative vorticity advection at high level and positive vorticity advection at low level formed by the forward inclining trough is very beneficial to the momentum spreaded downward from higher level,the greater the vorticity advection gradient in the vertical direction and the lower the gradient of large value center,the more likely it is to cause the occurrence of extreme wind near the surface in the west of the Hexi Corridor.