Mesoscale Cyclogenesis in Winter Monsoon Air Streams : Quasi-geostrophic Baroclinic Instability as a
Mesoscale Cyclogenesis in Winter Monsoon Air Streams : Quasi-geostrophic Baroclinic Instability as a
复制标题
冬季季风气流中的中尺度气旋发生:准地转斜压不稳定性
DOI：
10.2151/jmsj1965.70.1_77
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发表时间：
1992
影响因子：
3.1
通讯作者：
G. Wakahama
中科院分区：
文献类型：
--
作者：
K. Tsuboki;G. Wakahama
通过观测资料分析和线性不稳定性分析，研究了冬季季风气流中尺度气旋发生的机制。直径为200-700公里的中尺度气旋偶尔会在日本北海道西海岸附近形成。通过对卫星云图的分析，将中尺度气旋按水平尺度分为两类：I型(直径200~300公里)和II型(500~700公里)。观测研究表明，对流层下部的斜压性对中尺度气旋发生具有重要意义。本文用准地转方程组研究了具有纬向分量和经向分量的斜压流的不稳定问题。模式的基本气流表达了观测到的风廓线的基本要素。线性不稳定性分析表明，存在两个不稳定模：波长200-300公里的模式I和波长500-700公里的模式II。前者是由经向风分量的垂直切变引起的，后者主要是由纬向风分量的垂直切变引起的。理论和观测方面的比较表明，模式I和模式II可以分别解释类型I和类型II的特征性质。能量学结果表明，模式I和模式II都是通过涡旋可用势能的增加和涡动动能的转换来维持的。根据观测资料分析和线性不稳定分析，认为中尺度气旋是在特定斜压气流中发展起来的斜压不稳定扰动。
The mechanism of mesoscale cyclogenesis in winter monsoon air streams is studied by data analyses of observations and linear instability analysis. Mesoscale cyclones, with a diameter of 200-700 km, occasionally develop off the west coast of Hokkaido, Japan. Based on the analysis of satellite images, the mesoscale cyclones are classified into two types according to their horizontal scale: Type I (200-300 km in diameter) and Type II (500-700 km). The observational studies suggest that the baroclinicity in the lower troposphere is important for the mesoscale cyclogenesis. The quasi-geostrophic equations are used to investigate an instability problem of a baroclinic flow with both the zonal and meridional components. The basic flow of the model expresses the essential elements of the observed wind profiles. The linear instability analysis showed that two unstable modes are found: Mode I with a wavelength of 200-300 km and Mode II with 500-700 km. The former is caused by the vertical shear of the meridional wind component and the latter mainly by that of the zonal wind component. The comparisons between theoretical and observational aspects indicate that Mode I and Mode II can account for the characteristic properties of Type I and Type II, respectively. The energetics shows that both Mode I and Mode II are maintained by the increase of the eddy available potential energy and its conversion into the eddy kinetic energy. Based on the data analyses of observations and the linear instability analysis, we concluded that the mesoscale cyclones are baroclinic instability disturbances developing in a particular baroclinic flow.