一次大暴雨过程中低空急流演变与强降水的关系

利用营口新一代天气雷达提供的每6分钟一次的风廓线资料,详细分析了2006年6月29日辽宁省西部大暴雨过程中强降雨时段的低空风场结构。得出:此次强降水天气的发生与低空急流的迅速加强和向下扩展相对应,短时大暴雨发生前低空西南急流提前2小时左右开始有动量快速下传,当20m.s-1的急流中心下传到≤1km超低空,1.2～2.1km低空出现24m.s-1东南急流,有利于产生短时大暴雨;说明低空脉动及向地面扩展程度与短时强降水之间关系密切。低空急流到达测站上空不一定立即产生强降水,有时会滞后1～2个小时,强降水或强烈天气的发生都存在着一定的动量下传,引起低空扰动加强,同时低空急流的强度和伸展高度,以及动量下传的能量大小,都直接制约着强降水的强弱。低空急流指数增大的程度和降水量的强度呈正比关系,低空急流指数不仅可以说明低空急流的脉动以及向地面扩展程度与中小尺度的强降水存在密切的关系,同时对强降水的出现以及雨强的大小有一定的预示作用。

Mesoscale Structure and Evolution of the Low-level Jet and Its Relationship with the Heavy Rainfall During a Torrential Rain Process

Using the data of the wind profile delivered every six minutes by the new generation of weather radar of Yingkou,the detailed analysis is made for the low-level wind field structure during the heavy rain periods of torrential rains on 29 June 2006 in the west of Liaoning Province.The conclusion is as follows:The incidence of the heavy rain is corresponding to the rapid strengthening of low-level jet and its downward expansion.The southwest low-level jet in advance of two hours before the short-term heavy rain starts to move downward rapidly.The fluctuation in the low level and its degree of expansion towards the ground has a close relation to the strong short-term rainfall.The low-level jet will not certainly immediately cause a strong rainfall when it arrives at the station,sometimes this process will be delayed one or two hours.The emergence of the strong rainfall or the strong weather has definite momentum transmission.It strengthens the low-level disturbance and the strength of low-level jet.The extended height and the magnitude of the momentum transmission restrict directly the strength of the strong rainfall.The degree of increase in the low-level jet index(I)and the intensity of rainfall has a direct proportional relationship.Index(I)not only indicates that the fluctuation of low-level jet and the intensity of ground expansion have a close relationship with the strong rainfall of meso scale,but also indicates the occurrence of strong rainfall and the magnitude of rainfall intensity.