随机分布的小尺度涡对涡旋自组织影响的研究

以往双涡相互作用的动力学一般都在决定性的框架内研究。文中用一个平流方程模式,实施积分时间为30 h的8组试验,分析决定性和随机性共存系统中双涡相互作用和涡旋自组织的问题。随机性通过以下方式引入模式:先用Iwayama方案生成随机分布的小尺度涡,再将这些小尺度涡加入初始场。试验中,初始随机分布小尺度涡的强度参数K分别取0.0、0.4、0.6、0.8和1.0。结果表明,没有小尺度涡的条件下(K=0.0),初始分离的两个β中尺度涡逆时针互旋,其准终态流型是两个分离的涡;引进小尺度涡后,K取0.8、1.0时,初始分离强度相同的两个β中尺度涡,逐渐形成主次之分。主涡将次涡拉伸成为螺旋带,其准终态流型是一个自组织起来的类似于台风环流的涡旋。准终态涡中心的相对涡度值随K值的加大而加大。结果还表明,准终态流型不仅与初始小尺度涡的强度参数有关,而且与初始小尺度涡的分布有关。此外,在相同初始场的情况下,还实施了3类不同边畀条件的试验:第1类,在东西边界取周期条件,在南北边界取固定条件;第2类,在所有边界均取固定条件;第3类,在所有边界均取周期条件。这3类试验的准终态流型相同,都显示出一个类似于台风涡旋的环流。根据这些结果可以初步认为,涡旋自组织的研究从决定性动力学向随机动力学的过渡是值得探索的。

AN INVESTIGATION INTO EFFECT OF RANDOMLY DISTRIBUTED SMALL-SCALE VORTICES ON VORTEX SELF-ORGANIZATION

Previous studies concerning the interaction of dual vortices have been made generally in the deterministic framework.In this paper,by using an advection equation model,eight numerical experiments whose integration times are 30 h are performed in order to analyze the interaction of dual vortices and the vortex selforganization in a coexisting system of deterministic and stochastic components.The stochastic components are introduced into the model by the way that the Iwayama scheme is used to produce the randomly distributed small-scale vortices which are then added into the initial field.The different intensity of the smallscale vortices is described by parameter K being 0.0,0.4,0.6,0.8,and 1.0,respectively.When there is no small-scale vortex(K=0.0),two initially separated meso-beta vortices rotate counterclockwise mutually,and their quasi-final flow pattern is still two separated vortices;after initially incorporating small-scale vortices(K=0.8,1.0),the two separated meso-beta vortices of initially same intensity gradually evolve into a major and a secondary vortex in time integration.The major vortex pulls the secondary one,which gradually evolves into the spiral band of the major vortex.The quasi-final flow pattern is a self-organized vortex with typhoon-like circulation,and the relative vorticity at its center increases with increase in K value,suggesting that small-scale vortices feed the self-organized vortex with vorticity.This may be a possible mechanism responsible for changes in the strength of the self-organized vortex.Results also show that the quasi-final pattern not only relates with the initial intensity of the small-scale vortices,but also with their initial distribution.In addition,three experiments are also performed in the case of various boundary conditions.First,the periodic condition is used on the E-W boundary,but the fixed condition on the S-N boundary;second,the fixed condition is set on the all boundaries;and third,the periodic condition is chosen on the all boundaries.Their quasi-final flow patterns in the three experiments are the same each other,exhibiting a larger scale typhoon-like circulation.Based on these results mentioned,Authors think that the transition of vortex self-organization study from the deterministic system to the coexisting system of deterministic and stochastic components is worth exploring.