Excitation of Transient Rossby Waves on the Stratospheric Polar Vortex and the Barotropic Sudden Warming
Excitation of Transient Rossby Waves on the Stratospheric Polar Vortex and the Barotropic Sudden Warming
复制标题
平流层极涡上瞬变罗斯贝波的激发与正压突然增温
DOI：
10.1175/jas3557.1
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发表时间：
2005
影响因子：
3.1
通讯作者：
R. K. Scott
中科院分区：
文献类型：
--
作者：
J. G. Esler;R. K. Scott
本文在一个简单的准等转f平面模式中，对随时间变化的地形强迫对平流层极涡边缘的罗斯贝波的激发进行了解析和数值研究。当大气可压缩时，发现涡旋的线性响应有两个不同的组成部分。第一个是向上传播波的频谱，这些波是通过强迫在固定的“Charney-Drazin”范围内的时间频率激发的，该范围取决于涡旋边缘的角速度和涡旋汉堡数。响应的第二个组成部分是正压模态，它是由在Charney-Drazin范围外的固定时间频率的强迫激发的。这两个响应的相对大小，就总角伪动量而言，取决于力的水平尺度与罗斯比半径的比值。在典型的平流层条件下，发现正压响应占主导地位。非线性模拟证实，线性结果仍然与理解强烈非线性罗斯比破波发生时的响应有关。结果表明，当正压模态被共振激发时，与向上传播的波被激发时相比，在较低的强迫幅值下可以产生突然变暖或旋涡角伪动量的快速增加。本文描述了一个由相对较弱的地形强迫激发正压模态而引起的“正压突然变暖”的数值模拟。
The excitation of Rossby waves on the edge of the stratospheric polar vortex, due to time-dependent topographic forcing, is studied analytically and numerically in a simple quasigeostrophic f-plane model. When the atmosphere is compressible, the linear response of the vortex is found to have two distinct components. The first is a spectrum of upward-propagating waves that are excited by forcing with temporal frequencies within a fixed “Charney–Drazin” range that depends on the angular velocity at the vortex edge and the vortex Burger number. The second component of the response is a barotropic mode, which is excited by forcing with a fixed temporal frequency outside the Charney–Drazin range. The relative magnitude of the two responses, in terms of total angular pseudomomentum, depends on the ratio of the horizontal scale of the forcing to the Rossby radius. Under typical stratospheric conditions the barotropic response is found to dominate. Nonlinear simulations confirm that the linear results remain relevant to understanding the response in cases when strongly nonlinear Rossby wave breaking ensues. It is shown that a sudden warming, or rapid increase in vortex angular pseudomomentum, can be generated at much lower forcing amplitudes when the barotropic mode is resonantly excited compared to when the upwardpropagating waves are excited. A numerical simulation of a “barotropic sudden warming” due to excitation of the barotropic mode by a relatively weak topographic forcing is described.