A model study of the growth of summer monsoon disturbances

Using an appropriate north-south distribution of a diabatic heating in a global multilevel spectral model, we have generated summer monsoon type of basic flow. Then we superimposed a pulse at the point of inflexion to the north of the jet at 900 mb. Using conditional instability of the second kind (CISK) type of cumulus heating we integrated the model keeping the basic flow fixed. We found that the pulse grows into observed type of monsoon depression. When cumulus heating was absent the pulse did not show any appreciable growth. The detailed computations of energetics show that the main growth mechanism of the pulse is by baroclinic energy exchange in the presence of cumulus heating.