強烈非平行流的絕對不穩定度與平流不穩定度

The Absolute and Convective Instabilities of Strongly Non-Parallel Shear Flow

林和(Ho Lin) ； 曹志成(Chi-Chen Tsao)

《大氣科學》 16卷2期 (1988/06) Pp. 197-216

摘要

傳統流力不穩定度問題，大都假設流向均勻，如此求得的不穩定基側區域性偏好，若要解釋某些有利於旋生的位置就顯得不足。非平行流場之擾動與平行流場迥然不同。由於這種不均勻性生成的絕對不穩定度可促使擾動局部成長，而平流不穩定情況下，擾動在t→∞會經過測站而不停留，正是解釋擾動區域性的最佳候選。本文使用正壓模式研究強烈非平行流場的不穩定度，發現非平行性增強到某一程度時，流場由平流不穩定轉為絕對不穩定，擾動在原地呈指數成長。我們同時檢討在初始場增加高頻擾動的影響，以及加入β效應或追踪劑引致的異同，希望本文結果，能部份解是西南渦移動、停滯的動力因素。

關鍵字

絕對不穩定度 ； 平流不穩定度 ； 非平行風切流 ； 西南渦

並列摘要

The traditional flow instability problems are based on the assumption that the stream lines are parallel to each other, The resulted unstable mode will have no perferrence on any particular location streamwise. Vet the observed cyclogenesis always occur on some selected regions. Therefore the perturbations of non-parallel flow would differ from that of parallel flow in many fundamental ways. Due to this spatial inhomogeneity the so-called absolute instability can stay and grow at some locations, while the convection instability indicates that the growing wave packet will pass by a station eventually. The above criterion provides a possible explanation for regional perturbation.This study will use a barotropic model to study the instability of a strongly non-parallel flow. When we increases the non-parallelness, the flow jumps from convective instability to absolute instability, then the perturbations will stay at the unstable region, grow exponentially.

並列關鍵字

Absolute Instability ； Convective Instability ； Non-parallel Shear Flow ； Southwest Vortex