To send content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about sending content to .
To send content items to your Kindle, first ensure firstname.lastname@example.org
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about sending to your Kindle.
Note you can select to send to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Using a two-level quasi-geostrophic model, the effect of the inclusion of a long stationary monsoon wave (basic meridional wind) on the combined barotropicbaroclinic instability of the monsoon current has been investigated. Both barotropic and baroclinic interactions of the perturbation with the monsoon wave and the zonal flow are included. This analysis, using realistic velocity profiles, yields fast-growing westward-moving upper-tropospheric waves corresponding to easterly waves, and lower-tropospheric modes corresponding to monsoon disturbances.
The stability of the monsoon zonal flow has been studied by Shukla (1977) and Keshavamurty et al. (1977). They found that the monsoon atmosphere is not baroclinically unstable. Shukla found that the CISK mechanism can lead to a growth of disturbances of the same scale as the observed monsoon disturbances, but that there was no preferred scale with a fastest rate of growth. Keshavamurty et al. found that the monsoon zonal flow is barotropically unstable in the lower and midtroposphere and that this instability can yield disturbances of reasonable growth rate and scale. Mak (1975) studied the effect of the meridonal motion on baroclinic instability of a monsoon flow, but found that the meridonal components required for growth were very large compared to those obtained from observed winds. Lorenz (1972) studied the barotropic instability of Rossby waves and found that shorter waves can be barotropically unstable. The observed monsoon flow is seen to have an appreciable meridional component.
Active monsoon epochs over western India are often associated with cyclonic disturbances most marked in the midtroposphere. In order to understand the mechanism of their growth, linear barotropic, baroclinic and combined barotropic–baroclinic stability analyses of the mean flow in this region have been carried out. The potential vorticity of the mean flow shows extreme values in the region of the midtropospheric shear zone. The analyses yield barotropically unstable modes (i) at 700, 600, 500 mb and (ii) at 200 mb, with wavelengths of 20 to 30 degrees of longitude and doubling times of 3 to 4 days. Combined barotropicbaroclinic stability analyses using a 2-level quasi-geostrophic model yield essentially the same upper- and lower-tropospheric barotropically unstable modes, with only a marginal effect due to the presence of baroclinicity.
There seem to be certain parts of the monsoon region from southeast Asia to western India which are particularly cyclogenetic. Shukla (1977) and Keshavamurty et al. (1977) have carried out a general stability analysis of the monsoon zonal flow. It turns out that the zonal wind profile over western India shows some slightly different features compared to that, say, over southeast Asia. In the former longitudes, the heat low over northwest India–Pakistan is overlain by anticyclonic flow in the midtroposphere, so that there is an east–west shear zone in the middle levels. This feature is not so well marked over other longitudes in the monsoon region.
Email your librarian or administrator to recommend adding this to your organisation's collection.