一次东北冷涡过程的结构特征与降水关系分析

Analysis of the Relationship between Structures of a Cold Vortex Process and Rainfall over the Northeast China

利用FNL1°×1°逐6 h再分析资料、常规实况观测资料对近10年来一次最强典型东北冷涡区域性暴雨过程在东北冷涡环流演变不同阶段中的动力、热力、水汽条件及不稳定能量与降水的关系进行诊断分析。根据冷涡系统的环流特点,将冷涡过程划分为初生、发展、成熟和减弱等阶段。冷涡初生阶段,降水主要分布在垂直运动较强的位置,降水强度不大;发展阶段,斜压性较强,冷涡前部有大范围高层干冷平流、低层暖湿平流叠加,降水主要分布在冷涡前部切变辐合最强的位置,降水强度与低层辐合中心强度及垂直速度成正比;成熟阶段,冷涡演变为准正压结构,垂直上升运动的强度和范围都达最大,广泛分布在冷涡中心及前部,降水中心向冷涡中心移动,强度与发展阶段接近,该阶段降水与不稳定能量分布及中高层干冷空气入侵关系更为密切,但与动力因子相关程度下降;减弱阶段,降水变得分散,强度迅速减弱,与环流及物理量之间关系的规律不再显著。在冷涡演变的整个过程中,偏南、偏西及偏东的水汽通道对水汽的输送和集中是此次强降水得以发生发展的必要条件,其中偏南气流带来的水汽净流入是此次降水过程的主要水汽来源,降水区水汽净收入与降水强度之间存在明显的正相关关系。

Based on conventional observations and the FNL reanalysis data,this paper analyzes the relationship between the rainfall characteristics and the circulation of a cold vortex during different phases for the strongest cold vortex associated rainstorm in recent 10 years over the northeast China.In general,the rainfall distribution is closely related to the dynamical and thermal conditions and water vapor distribution in a cold vortex process.The cold vortex process can be divided into four phases,the formation,developing,mature,and dissipating phase,respectively.In the formation phase,the precipitation is mainly confined in the area with strong vertical movement,but the precipitation rate is small.In the developing phase,the baroclinic condition is strong.Over the front part of the cold vortex there are strong dry and cold advections in the upper level and warm and wet advections in the lower level.Intensive rainfall is mainly distributed in the front of the cold vortex where the convergence is the strongest.The precipitation rate shows a direct proportional relationship to the strength and vertical velocity of the convergence center in the lower level.In the mature phase,the cold vortex is quasi-barotropic.The intensity and range of the vertical velocity are the largest,the precipitation is widely distributed in the center and front of the cold vortex.The precipitation center moves towards the center of the cold vortex,and its intensity is similar to that during the developing phase.The precipitation distribution is more related to the distribution of unstable energy and dry cold air than to the dynamical conditions.In the dissipating phase,the precipitation is scattered and its intensity decreases rapidly,and its relationship with circulation and other conditions is no longer significant.For this case,the convergence of water vapor from the south,west and east played an essential role in the evolution of the cold vortex.The inflow of water vapor from the south was the main water vapor source for the strong rainstorm.There was significant positive correlation between the net inflow of water vapor and the intensity of precipitation.