斜压气流的中尺度稳定性 Ⅱ.横波型不稳定

本文是“斜压气流的中尺度稳定性”的第二部份,讨论基本流对横波型中尺度扰动的稳定性.将f-平面的Eady模型推广到非地转情况,得到斜压基流的双模态不稳定谱:在天气尺度和次天气尺度上出现Eady模态,在几十至几百公里的惯性尺度上出现非地转斜压中尺度模态.在垂直剖面上中尺度模态呈非对称“猫眼”流型,在水平方向上散度与涡度交替分布.对同一线性风速廓线,中尺度模态的发展率约为Eady模态的4倍,两种扰动发展的主要能源都是旋转基流中储存的斜压有效位能.

ON MESOSCALE INSTABILITY OF A BAROCLINIC FLOW 2. TRANSVERSAL INSTABILITY

The second part of the present study investigates instability of a baroclinic basic flow against the transversal mesoscale disturbances. By generalizing the Eady model to an ageostrophic one, the bi-mode and even mufti-mode instability spectra may occur for a baroclinic basic flow. The Eady-mode appears at synoptic scales, whereas the ageostrophic, baroclinic mode appears at inertial scales ranging from sevenal tens to hundreds kinometers. The Eady-mode, with a qrasi-geostrophic structure, has a larger vertical depth, while the meso-modes are mostly confined to the middle and lower troposphere with an asymmetric "cat eyes" pattern in the vertical cross section and an alternative distribution of divergence and vorticity in the horizontal plane. The growth rate of the mesoscale mode is about four times larger than that of the Eady-mode for the same wind profile of linear distribution. the major energy source, which supports these two modes, is the baroclinic available potential energy stored in a rotating basic flow. The results of this paper may be useful in analysis of the mesoscale distur-bances'propagating along a basic flow.