夏季副热带高压北移的非线性机理探讨

PRIMARY STUDY OF THE NONLINEAR MECHANISM ABOUT SUMMER SUBTROPICAL HIGH MOVING NORTHWARD

文中建立了含22个变量的强迫、耗散、非线性的斜压大气动力系统。该系统包含了超长波、长波和纬向气流三者的相互作用;反映了北半球两大洋、两大陆的“二波型”的纬向和经向非均匀热力强迫;采用相轨线图、流函数图以及Poincar啨图相结合的方法,归纳出若干典型的流动体制和环流型式;用长方形通道中的流动近似地表征北半球环流。结果表明:(1)该系统能很好地刻画斜压大气中7种流动体制及其转换;随着夏季热力强迫的增大,系统状态经历了R1R12V-NVR12的变化。(2)刻画了4种主要的环流型式及其转换;随着夏季热力强迫的增大,环流型从G2转G3,即副高季节性北移西伸。(3)系统的流动体制和环流型式之间的联系表现为:夏季副热带高压北移西伸即G2转G3的变化,对应着流动体制由Rossby流转振荡态(R12V-NV);副热带高压在偏北位置上的南北向和东西向的振荡活动,则对应着系统振荡态的维持。

One of the most characteristic atmospheric circulation processes is that summer subtropical high over Pacific moves northward and extends westward, which affects China’s weather and climate significantly. Subtropical high over Pacific moves northward by the effect of meridian heating field changing from June to August each year. It is the seasonal catastrophe of the Northern Hemisphere to global atmospheric circulation, especially by jumping northward. Mechanism of summer subtropical high moving northward was discussed by applying dynamical system theory and method. Baroclinic atmospheric system containing ultra-long wave, long wave and zonal current interacted was built firstly, then phase trajectory figure, stream function figure, Poincaré section map and phase variable time graph were used to analyze the evolving of system states and circulation patterns, especially to examine subtropical high and its moving northward seasonally, by the effect of summer zonal inhomogeneous inposed thermal field together with friction dissipation. The nonlinear system theory and method were used to discuss subtropical high variation mechanism and new research were explored:(1)the higher steps dynamical system(22 variance) considering ultra-long wave,long wave and zonal flow which interacted was built.(2)it was designed to a summer inhomogeneous thermal field of two-ocean and two-continent in the Northern Hemisphere.(3)The system states were analyzed synthetically by phase trajectory figure,Poincaré section map and phase variable time graph, and the states distribution of parameter plane (θ*K,k) was drawn, and stream function isoclines graph of rectangle passage(to be shown as the Northern Hemisphere approximately) was also drawn by renewed stream function.Several characteristic circulation patterns were sum up,and the distribution of circulation patterns were acquired with the plane(θ*K,k).Subtropical high moving northward was discussed by combining system states and circulation patterns.The main results were as follows: (1) There were seven regimes of flow,and states came through HR1R 12 V-NVC along with value k minish,and through R1R 12 V-NVR 12 along with value θ*K increase.(2) There were four circulation patterns,and patterns came through WG1G2G3 along with value k minish,and through G2G3 along with value θ*K increase.(3) It was represented that circulation pattern came through G2 to G3 for summer subtropical high moving northward and extending westward,and it was that regimes of flow transformed Rossby regimes into vacillation states (R 12 V-NV) corresponding to that change.Transmeridional and south-north vacillation movement where subtropical high was leaning to north was corresponding with maintaining vacillation states. The system,which was established in this paper,was capable of depicting the regimes of flow and circulation patterns of special season.It revealed the possible mechanism of subtropical high moving northward seasonally and vacillation in certain season,which was forced,dissipative and nonlinear atmospheric system transferred from waves to vacillation and to be kept. There are several questions to be discussed as follows:(1) The results above belong to the category of dynamic systemic qualitative analysis and numerical experiment, and it makes the system closed to the actual instance because of considering the effect of long wave and zonal heterogeneous field. It helps to understand the mechanism of subtropical high deeply. (2) Rectangle passage flow was used to replace flow regimes of annulus passage approximatively, then to replace the Northern Hemisphere circulation. These problems should be improved more.