Upper-Tropospheric Synoptic-Scale Waves. Part II: Maintenance and Excitation of Quasi Modes
Upper-Tropospheric Synoptic-Scale Waves. Part II: Maintenance and Excitation of Quasi Modes
复制标题
对流层上层天气尺度波。
DOI：
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发表时间：
1992
期刊：
影响因子：
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通讯作者：
B. Farrell
中科院分区：
文献类型：
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作者：
Chantal Rivest;B. Farrell
摘要在前一篇论文中，提出了一个维持对流层上层波的简单动力学模型：高层Eady简正模。在本文中，它表明，这些模式具有对应的基本状态与正对流层位涡梯度，这些对应物可以保持和激发的时间尺度与观测一致。当对流层位涡梯度为无穷小正值时，高层简正模解不再存在。当梯度为无穷小时，正态模解消失，这代表了一个明显的奇异性，并挑战了与上层Eady正态模相关的上层天气尺度波的解释。在一系列的初始值试验中，研究了在对流层位涡梯度存在的情况下，上层模态解会发生什么。我们的结果表明，它们成为缓慢衰减的准模。在数学上，准M…
Abstract In a preceding paper a simple dynamical model for the maintenance of upper-tropospheric waves was proposed: the upper-level Eady normal modes. In this paper it is shown that these modes have counterparts in basic states with positive tropospheric gradients of potential vorticity, and that these counterparts can be maintained and excited on time scales consistent with observations. In the presence of infinitesimal positive tropospheric gradients of potential vorticity, the upper-level normal-mode solutions no longer exist. That the normal-mode solution disappears when gradients are infinitesimal represents an apparent singularity and challenges the interpretation of upper-level synoptic-scale waves as related to the upper-level Eady normal modes. What happens to the upper-level modal solution in the presence of tropospheric gradients of potential vorticity is examined in a series of initial-value experiments. Our results show that they become slowly decaying quasi modes. Mathematically the quasi m...