Abstract:

Based on the conventional observation data, automatic weather precipitation data, Doppler radar data and NCEP reanalysis data with 1°×1° spatial resolution, the formation mechanism of the low vortex on the north side of Guizhou Plateau under influence of north path cold air on May 22, 2017 was discussed. The results were as follows: (1) The terrain led to the cold air return and formed an occluded front. There was a low vortex between the surface and 800 hPa, which formed above the occlusion front, it  belonged to warm and shallow meso-β-scale vortex system. (2) The low vortex maintained for 2 days, the precipitation occurred near the center of the vortex and its intensity was not strong. (3) The development of the vorticity and maintenance of low-level vortex system were associated with fluctuation in the middle and upper atmosphere. When it turned to the northwest airflow on the upper layer, the development of vorticity was suppressed and the cold air invasion made the low vortex weaken and dissipate. (4) The evolution process of the vortex could be divided into three stages: terrain backflow, occlusion development, weakening and demise. There were significant differences between this vortex and southwest low vortex ,frontal cyclone in the formation mechanism, rainfall area and intensity.

Key words:  terrain effect, cold air return, occluded front, low vortex precipitation

摘要：

利用常规观测资料、地面加密自动站降水资料、多普勒天气雷达资料以及NCEP1°×1°再分析资料对2017年5月22—25日一次偏北路径冷空气影响下贵州高原北侧低涡的形成机制进行探讨。结果表明：（1）地形导致冷空气回流形成地形锢囚，锢囚锋上有低涡产生，位于地面至850 hPa的大气低层，属于暖性浅薄中-β尺度系统；（2）低涡维持2 d，降水产生在低涡中心附近，雨强不大；（3）中高层波动强迫低层涡度发展而使低涡维持；当中高层转为西北气流时，涡度发展受抑制且冷空气侵入低涡而使其减弱消亡；（4）低涡形成过程可分为地形回流、锢囚发展和减弱消亡3个阶段，与西南低涡及锋面气旋在形成机制、降水落区和强度等方面存在明显差异。

关键词: 地形作用, 冷空气回流, 锢囚锋, 低涡降水