Stratospheric Sudden Warmings as Self-Tuning Resonances. Part II: Vortex Displacement Events
Stratospheric Sudden Warmings as Self-Tuning Resonances. Part II: Vortex Displacement Events
复制标题
平流层突然变暖作为自调谐共振。
DOI：
10.1175/jas-d-11-08.1
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发表时间：
2011
影响因子：
3.1
通讯作者：
Matthewman N
中科院分区：
文献类型：
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作者：
Matthewman N
在非弹性大气中准地转柱状涡的理想化模型中研究了涡位移平流层突然变暖（SSW）。由于观测到的事件发生在地球表面的固定方向并具有强烈的斜压垂直结构，涡旋罗斯贝波受到固定地形强迫的驱动，该强迫旨在最大限度地减少涡旋相对其初始位置的偏移。背景平流层“气候”的变化通过固体旋转中的附加流动来表示。涡流响应在数值上确定为强制强度和背景流强度 Ω 的函数。在中等强度下，发现仅在较窄的 Ω 范围内才会出现具有许多类似于观察到的位移 SSW 的特征的大响应。线性分析表明，对于这个 Ω 范围，第一斜斜方位角波-1 罗斯贝波模式接近于共振激发。提出了受迫非线性振子方程来描述非线性行为，并采用了一种利用稳定传播涡旋“V 态”的非受迫计算来数值确定相关系数的方法。非线性方程预测有限 M 下响应变化的一些定性细节。然而，得出的结论是，强非线性过程（例如波破碎和细丝形成）对于确定有限 M 下的近共振响应的幅度在数量上必然是重要的。
Vortex displacement stratospheric sudden warmings (SSWs) are studied in an idealized model of a quasigeostrophic columnar vortex in an anelastic atmosphere. Motivated by the fact that observed events occur at a fixed orientation to the earth’s surface and have a strongly baroclinic vertical structure, vortex Rossby waves are forced by a stationary topographic forcing designed to minimize excursions of the vortex from its initial position. Variations in the background stratospheric “climate” are represented by means of an additional flow in solid body rotation. The vortex response is determined numerically as a function of the forcing strengthMand the background flow strength Ω.At moderateMit is found that a large response, with many features resembling observed displacement SSWs, occurs only for a narrow range of Ω. Linear analysis reveals that for this range of Ω the first baroclinic azimuthal wave-1 Rossby wave mode is close to being resonantly excited. A forced nonlinear oscillator equation is proposed to describe the nonlinear behavior, and a method for determining the relevant coefficients numerically, using unforced calculations of steadily propagating vortex “V states,” is adopted. The nonlinear equation predicts some qualitative details of the variation in the response at finiteM. However, it is concluded that strongly nonlinear processes, such as wave breaking and filament formation, are necessarily quantitatively important in determining the amplitude of the near-resonant response at finiteM.