The above analysis showed that this heavy rainfall event took on obvious meso - scale characters and was the combination of the three flows , so we can deduce : ( 1 ) surface southeasterly wind and topography may play the main role in this event ; ( 2 ) the easterly cold air rushing into the southern shaanxi province in the lower troposphere was strongly relative to the form of surface cold - front type of occlusion ; ( 3 ) there were two reasons for the secondary circulation ' s strengthen in the evening , one was the effect of a mountain - valley wind and the other may be latent heat leading to ascending motion ; ( 4 ) the shape of potential instability stratification corresponded well with the development of the warm - moisture advection ; and ( 5 ) the vapor providing essential thermodynamics was transported by a southwesterly low - level jet from the bay of bengal and the south china sea . furthermore , with the effect of terrain , the southern shaanxi province became the center of this extremely heavy rain process 中尺度结构分析表明，本次暴雨具有明显的中尺度特征，是由三支气流共同作用的结果，分析发现( 1 )地面东南风和地形在这次大暴雨过程起主要作用； ( 2 )东路冷空气主要是通过中低层侵入陕南地区的，并与地面冷式锢囚锋的形成密不可分； ( 3 )夜博士论文:中尺度地形对陕南暴雨的影响研究间垂直次级环流发展加强可能有两个原因，一个是由于地形山谷风的作用，另一个是降水的潜热释放激发了上升运动: ( 4 )位势不稳定层结的形成与低层暖湿平流的发展有很好的对应关系; ( 5 )本次暴雨的水汽主要靠偏南风急流将孟加拉湾和中国南海的水汽输送至西北地区东部，为暴雨的发生提供了必要热力条件。
