飓风“桑迪”温带变性过程特征分析

Characteristics of extratropical transition of hurricane Sandy

利用NCEP的1°×1°资料,分析飓风"桑迪"温带变性前后物理量的特征和变化。结果表明:利用对流层低层、中层及高层的厚度场可立体直观地展现热带气旋中心热力结构的对称性,便于进行飓风温带变性的诊断分析。涡度场可诊断高空槽和飓风耦合的情况,两者的正涡度场连接后使热带气旋受到高空槽的影响开始变性。厚度变形场动力强迫上升、低层锋区抬升、强降水区凝结潜热正反馈作用和高空辐散加强等有利于飓风"桑迪"变性过程中深对流的维持及发展,并导致强上升区域向西偏离。飓风"桑迪"变性后暖心结构下降至对流层中低层,与强上升运动中心下降有关。适度的冷空气强度对飓风"桑迪"的加强有利,冷空气较弱飓风加强较慢,冷空气过强易破坏飓风的暖心结构,导致中心填塞。850 h Pa温度平流对变性后飓风"桑迪"的移动路径有一定的指示意义,飓风基本朝着冷平流中心指向暖平流中心的方向移动。

Based on the 1° × 1° NCEP reanalysis data,characteristics of extratropical transition of hurricane Sandy were analyzed. The results indicate that thermal asymmetry of extratropical transition system is displayed directly using thickness fields in low,middle and upper levels of the troposphere,which is favorable to diagnose the extratropical transition of hurricane. Vorticity field could diagnose the coupling of upper-level trough and hurricane,and the extratropical transition begins because the hurricane is impacted by the baroclinic trough after the combination of their positive vorticity. The strong convection during the process of extratropical transition could be enhanced by forced rising of thickness deformation field,lifting of lower frontal zone,positive feedback of condensation and increasing upper divergence,which are also reasons of westerly deviation of strong upwarding zone. The warm core of hurricane Sandy falls to the middle and lower levels of the troposphere,which is associated with the sink of strong ascending motion. The warm core can be ruined by strong cold advection,but moderate cold air advection is in favor of Sandy ＇ s redevelopment. Temperature advection distribution at 850 h Pa is indicative to Sandy ＇ s track during the extratropical transition process,which approximately parallels the connection between warm and cold advection centers.