R N Keshavamurty
Articles written in Journal of Earth System Science
Volume 87 Issue 3 March 1978 pp 61-75
The structure of the monsoon depression and the observed flow features prior to and at the time of monsoon depression formation (composite of 15 depressions) are examined. The composite monsoon depression (transient eddy) has a scale of 25° longitude and extends up to 300 mb and has the greast intensity at 700 mb. It shows north-north-east to south-south-west tilt in the lower levels indicating that it may draw upon zonal kinetic energy for its growth. The disturbance has lower temperatures to its west and tilts westwards with height indicating that eddy available potential energy is not converted from zonal available potential energy by large scale advection. There appears to be a reduction of vertical shear at the time of formation of monsoon depressions and this possibly aids cumulus convection.
The profiles of potential vorticity indicate extremes (i) in the upper troposphere and (ii) at several midtropospheric levels in the region of the monsoon trough indicating the possibility of combined barotropic-baroclinic instability. Using multi-level quasi-geostrophic model and employing the eigin-value technique it is shown that the monsoon zonal current is not
Volume 89 Issue 2 July 1980 pp 209-214
During our search for dynamical differences in monsoon flows between the active and break phases of the monsoon, we noticed some interesting differences which may have some dynamical significance and do not appear to have been highlighted so far. There appear to be shifts of quasi-stationary flow features both in the lower and upper tropospheres.
Volume 90 Issue 3 November 1981 pp 305-326
Using shallow water equations on an equatorial beta plane, the nonlinear dynamics of the equatorial waves is investigated. A general mathematical procedure to study the nonlinear dynamics of these waves is developed using the asymptotic method of multiple scales. On faster temporal and spatial scales the equations describe the equatorial waves
Volume 92 Issue 2 July 1983 pp 115-119
Barotropic stability of a stationary Rossby wave of wavelength 30° longitude superposed on the uniform monsoon zonal flow has been examined. The wave is unstable to perturbations and the growth rate depends on the meridional scale. These perturbations grow by drawing on the kinetic energy of the stationary Rossby wave.
Volume 97 Issue 2 December 1988 pp 127-136
A highly simplified zonally symmetric system of equations is used to understand the basic mechanism of the northward movement of the 30–50 day oscillation in the Indian monsoon region. Zonally symmetric perturbations are used on the July mean basic flow in the Indian region. A two-level model is employed. A simple parametrization of cumulus heating is included. An expression is derived for the northward phase speed. A right order of magnitude for the phase speed is obtained. The northward movement appears to be controlled by the basic zonal wind profile and cumulus heating.
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