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环境参量对广义Eady模态不稳定的影响
INFLUENCEOF ENVIRONMENT PARAMETERS ON INSTABILITY OF GENERALIZED EADY' S MODEL
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摘要: 介绍了广义Eady模态的斜压不稳定问题并着重讨论了环境参量对该不稳定的影响。该模态不仅存在有类似于经典Eady模态的不稳定短波截断, 还存在有经典Eady模态中没有的长波截断, 前者对环境参量的变化不太敏感而后者对环境参量的变化敏感。层结参数的减小, 模式底基流垂直切变的增大, 纬度的增高和模式层顶高度的减小, 均有利于该模态不稳定的发生。广义Eady模态下的最不稳定波仍发生在天气尺度波段, 其振幅和位相随高度的变化大体与标准Eady模态类似, 等位相线也随高度西倾, 但振幅关于大气中层不再呈对称性。Abstract: The baroclinic instability in generalized Eady's models is introduced and the influence of environment parameters on the instability is emphatically discussed. Not only in the model there exists the "short-wave cut-off" phenomenon similar to the classical Eady's model, but also there exists the "long-wave cut-off" phenomenon, which does not exist in the classical Eady's model. The former is not almost sensitive to environment parameters, but the latter is. The decrease of static stability parameter, the accretion of the vertical shear of the basic flow in the model bottom, the increase of latitude and decrease of the height of the model top are propitious to the instability in the model. The most instability in the generalized Eady's model appears in the synoptic scale wave range. The variations of amplitude and phase with altitude are analogous to those of the classical Eady's model. The isophase lines incline to west with altitude, but the amplitude is not symmetrical about the middle-level atmosphere.
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Key words:
- Environment parameters;
- Generalized Eady's model;
- Instability
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表 1 v1和v 2随N2的变化 (N2单位为10-5 s-2)
表 2 v1和v2随H的变化
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[1] Eady E T. Long waνes and cyclone waνes. Tellus, 1949, 79:267-269. [2] Charney J G. The dynamics of long waνes in a barocline westerly current. J.Meteor., 1947, 4:135-163. [3] Lindzen R. Nonlinear stability of zonally symmetric quasi-geostrophic flow. Adν.Atmos.Sci., 1994, 16:107-118. [4] Mu M, Shepherd T G. Nonlinear stability of Eady's model. J. Atmos. Sci., 1994, 51:3427-3436. doi: 10.1175/1520-0469(1994)051<3427:NSOEM>2.0.CO;2 [5] Liu Y M, Mu M. Nonlinear stability theorem for Eady's model of quasi-geostrophic baroclinic flow. J.Atmos.Sci., 1996, 53:1459-1463. doi: 10.1175/1520-0469(1996)053<1459:NSTFEM>2.0.CO;2 [6] Liu Yongming, Mu Mu. Nonlinear stability of generalized Eady's model. J.Atmos.Sci., 2001, 58(4): 821-827. doi: 10.1175/1520-0469%282001%29058%3C0821%3ANSOTGE%3E2.0.CO%3B2 [7] Pedlosky J. Geophysical Fluid Dynamics. by Springer-Verlag New York Inc. Printed in the United States of America. 1979. -
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