Role of barotropic,baroclinic and combined barotropic-baroclinic instability for the growth of monsoon depressions and mid-tropospheric cyclones |
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| Authors: | B. N. Goswami R. N. Keshavamurty V. Satyan |
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| Affiliation: | (1) Physical Research Laboratory, 380 009 Ahmedabad;(2) Present address: Department of Meteorology, Massachusetts Institute of Technology, 02139 Cambridge, Mass., USA;(3) Present address: Geophysical Fluid Dynamics Program, Princeton University, P.O. Box 308, 08540 Princeton, N.J., USA |
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| Abstract: | A detailed barotropic, baroclinic and combined barotropic-baroclinic stability analysis has been carried out with mean monsoon zonal currents over western India, eastern India and S.E. Asia. The lower and middle tropospheric zonal wind profiles over western India are barotropically unstable. The structure and growth rate of these modes agree well with the observed features of the midtropospheric cyclones. Similar profiles over eastern India and S.E. Asia, however, are barotropically stable. This is attributed to weak horizontal shear, inherent to these profiles. The upper tropospheric profiles, on the other hand, are barotropically unstable throughout the whole region. The features of these unstable modes agree with those of observed easterly waves. The baroclinic and combined barotropic-baroclinic stability analyses show that the baroclinic effects are not important in tropics. Though the barotropic instability of the mean zonal current seems to be res ponsible for the initial growth of the mid-tropospheric cyclones, neither barotropic nor baroclinic instability of the mean zonal current seem to explain the observed features of the monsoon depressions. |
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| Keywords: | Monsoon depressions mid-tropospheric cyclones mean zonal flows barotropic baroclinic instability |
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