A Possible Mechanism of the Genesis and Development of Meso-β Rainstorm System Part I. Phase Velocity of Vortex Rossby Waves
A Possible Mechanism of the Genesis and Development of Meso-β Rainstorm System Part I. Phase Velocity of Vortex Rossby Waves
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发表时间：
2005
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通讯作者：
Shen Xin
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作者：
Shen Xin
利用纬向基流中横波型扰动的Boussinesq近似方程，分析了当沿基流传播的中尺度扰动变得不稳定时，大尺度大气背景流场垂直分布的各种特征。有证据表明，1)在更稳定的分层下，如果基本流在低层和高层移动得更快（特别是在那里有射流存在的情况下），则产生的中观-β非定常波相对于基本流向东传播，甚至比基本流传播的速度更快；2)基流垂直风速切变引起行波管扰动的不稳定性；3)考虑基流风相对于z的二阶导数（记为{{0}，以下简称为β{{*}），得到相对于基流单向传播的涡状罗斯比波（VRoW）相速度表达式；4) VRoW的物理起源来自β _ _ _ *，即来自基本流场y方向平均涡度的z变非均质性；5) VRoW相速度与纬向波数k有关，能量弥散，群速度在x方向存在；6)当风速满足β _ *条件时，行波管扰动不稳定可能是VRoW和重力波混合扰动不稳定；7)当基本流受线剪切作用，但不满足β _ _ _ _ *条件时，行波管不稳定为惯性-重力波不稳定。
In the context of the Boussinesq approximation equations for transversal wave-type (TWT) disturbances in zonal basic flow, it is analysed that the various features in vertical distribution of a large-scale atmospheric background flow field when a meso-scale disturbance propagating along basic flow becomes unstable. Evidence suggests that 1) under more stable stratification, the basic flow, if moving faster at low and high levels (particularly in the presence of jets there), allows a resulting meso-β unsteady wave to propagate eastward with respect to basic flow and even at greater velocity compared with it; 2) vertical windspeed shear of basic flow causes instabilities of the TWT perturbation; 3) considering the second derivative of basic-flow wind with respect to z (denoted by zz≠ 0 which is simply given as β* hereafter) the expression for the phase velocity of vortex Rossby wave (VRoW) is obtained, which is unidirectional in propagation with respect to basic flow; 4) VRoW has its physical origin from β*, i.e., from z-varying heterogeneities of y-direction averaged vorticity of the basic flow field; 5) VRoW phase velocity is associated with zonal wave number k, its energy is dispersive and the group velocity exists in the x direction; 6) when windspeed meets the condition of β*, TWT disturbance instability may be that of mixed VRoW and gravity wave; 7) if basic flow is subject to linear shear but does not meet the condition of β*, the TWT instability is that of inertia-gravity wave.