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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| Institution: | (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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