An instability study of the onset‐vortex of the southwest monsoon, 1979
An instability study of the onset‐vortex of the southwest monsoon, 1979
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DOI：
10.3402/tellusa.v34i4.10822
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发表时间：
1982-08
期刊：
影响因子：
--
通讯作者：
M. Mak;C. Kao
中科院分区：
文献类型：
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作者：
M. Mak;C. Kao
本文用一个干的两层线性平衡模式研究了1979年西南季风爆发初期阿拉伯海纬向气流水平切变和垂直切变的相对影响。基本状态是从MONEX数据中获得的。在季风爆发之前的气旋生成的两个方面可以用主要与基流水平切变有关的动力不稳定过程来充分解释。这两个方面是扰动的增长率和尺度选择。在这个程度上，这项研究的结果与Krishnamurti等人（1981）的结果一致。但主要的正压不稳定机制错误地预测了气旋生成的其他两个方面。扰动的最大强度预计在急流南侧，扰动的垂直范围基本上局限于对流层低层。这些差异反映了干模型的局限性。垂直切变和层结对扰动的结构有显著影响，但对增长率的影响不大。线性平衡模式的结果与准地转模式的结果的比较表明，充分的变化的Coriolis参数随纬度应保留在未来的建模的爆发涡。DOI：10.1111/j.2153-3490.1982.tb01825.x
A dry two-layer linear-balanced model is used to investigate the relative effects of the horizontal and vertical shears of the zonal flow over the Arabian Sea in the early phase of the onset of the southwest monsoon in 1979. The basic state is obtained from the MONEX data. Two aspects of the cyclogenesis which immediately preceded the onset of the monsoon can be adequately accounted for by the process of dynamic instability mainly associated with the horizontal shear of the basic flow. These two aspects are the growth rate and the scale selection of the disturbance. To this extent, the results of this study agree with Krishnamurti et al. (1981). But the mainly barotropic instability mechanism incorrectly predicts two other aspects of the cyclogenesis. The maximum intensity of the disturbance is predicted on the southern flank of the jet and the vertical extent of the disturbance is essentially confined to the lower troposphere. These discrepancies reflect the limitations of a dry model. The vertical shear and stratification significantly influence the structure of the disturbance although their effect on the growth rate is small. The comparison of the linear-balanced model results with the quasi-geostrophic model results suggests that the full variation of the Coriolis parameter with latitude should be retained in future modeling of the onset-vortex. DOI: 10.1111/j.2153-3490.1982.tb01825.x