两次引发辽宁暴雪过程低涡的动力发展机制

Dynamic Diagnosis on Formation and Developing Mechanism of Two Vortices Causing Snowstorms in Liaoning

应用NCEP FNL分析资料,从动力学角度对2015年初辽宁地区两次低涡暴雪过程(简称"2.16"和"2.25"过程)的形成机制进行分析。结果表明:两次过程共同特点是850 hPa附近有低涡生成或加强,低涡是暴雪引发的直接原因。两次过程促使低涡生成的正涡度变率增大原因存在差异,"2.16"、"2.25"过程中对正涡度变率贡献最大的强迫项分别是散度项和涡度垂直输送项。500 hPa低涡东移,冷平流使得涡底部高空槽加深,槽前正涡度平流加强,差动涡度平流增大使得上升运动发展,导致850 hPa高度附近辐合增强是"2.16"过程正涡度变率增长、低涡生成的动力机制。强烈上升运动,对低层正涡度垂直输送,则是"2.25"过程850 hPa附近低涡形成和加强的动力机制。

By using National Centers for Environmental Prediction（NCEP） Final（FNL） operational global analysis data,the formation and developing mechanisms of the two vortices that caused snowstorms,on 16 and 25 February 2015 are investigated in terms of dynamics diagnosis.The results show that the formation and strengthening of vortices are the direct causes for the snowstorms,but the associated mechanisms are quite different in the two snowstorm cases.Positive tendencies of relative vorticity caused by convergence in lower troposphere and vertical transportation are the mainly forcing items for the formation of vortices in the two cases,respectively.On 16 February,there was a vortex moving eastward at 500 hPa.The cold advection near the bottom of the vortex deepened the trough at 500 hPa and the positive vorticity advection strengthened.Therefore,the increase of differential vorticity advection resulted in the developing of upward motion,and then the enhancement of the convergence at 850 hPa.On the other hand,on 25 February,the vertical vorticity transport by strong upward movement was the major developing mechanism of the vortex at 850 hPa.