非轴对称双涡相互作用的研究

在平流动力学的框架内,用准地转正压涡度方程模式实施了19组试验,研究双涡合并的条件及较大尺度涡旋自组织的问题。结果指出:(1)存在着两个影响双涡合并的因素,即初始双涡中心之间的距离和初始涡旋的非轴对称分布。初始两个对称涡旋合并具有明显的临界距离效应,但初始两个非轴对称涡旋能否合并还受到初始涡旋的非对称结构的复杂影响。(2)存在着两类不同的较大尺度涡旋的自组织过程,形成较大尺度涡旋。第一类,初始两个涡旋相同,均呈轴对称分布。双涡作用经历了缓变、快变,以及涡量羽翼的生成、拉伸和发展的过程,合并后呈对称性流型;终态涡内区涡量的堆积来源于两个初始涡,终态涡外区的螺旋带来源于两个初始涡外缘线涡量羽翼的拉伸。第二类,初始两个涡旋不同,一个为椭圆型,一个为偏心型,均呈非轴对称分布。双涡作用中,椭圆涡一边互旋,一边向计算区域中心靠近,同时涡量范围加大,形成了终态涡的内核区;偏心涡一边互旋,一边被不断拉伸,形成了终态涡的螺旋带区;表现出终态涡内区的涡量堆集来源于椭圆涡,终态涡外区螺旋带主要来源于偏心涡的反复拉伸及断裂的特性。

A STUDY ON THE INTERACTION OF NON-AXISYMMETRIC BINARY VORTICES

In the context of advection dynamics, nineteen experiments are performed using a quasi-geostrophic barotropic vorticity equation model to explore the condition for binary-vortex mergence, and the self-organization of the vortex of larger scale. Results show that the initial distance between the two vortices and the non-axisymmetric distributions of initial vorticity were two factors affecting the merger of binary-vortex. The self-organization process can be classified into two types. One type is that undergoing the processes of slowly change, rapid change, and the formation, stretch, and development of the fringe wing of vortex,two identical axisymmetric initial vortices merged into an symmetric vortex, with its vorticity piled up in the inner region coming from the two initial vortices, and in the spiral band in the outer region from the stretch of fringe wings. And the other is the merging of the two non-axisymmetric initial vortices of an elliptic vortex and an eccentric vortex, that is to say, in the interaction process of the binary-vortex, the elliptic vortex on one hand mutually rotated, on the other hand moved towards the center of the computational domain, expanded its vorticity range, and formed the inner core region of resultant vortex; and the eccentric vortex mutually rotated, meanwhile continuously stretched, finally formed the spiral band of resultant vortex.