Structure and Dynamics of Two Monsoon Depressions. Part II: Vorticity and Heat Budgets

Abstract

This paper discusses selected aspects of the vorticity and thermal fields of the two depressions described in Part I. The growth rate of the onset vortex is shown to be about three times that of the July depression. The most significant difference between the evolution of the two depressions lay in the growth rate at 500 mb, with the onset vortex showing a large vorticity increase and the July monsoon depression only a small increase. Vorticity budgets of the rain areas west of each depression's center showed that the observed westward motion of the depressions resulted from dominance of the divergence term in the lower troposphere. Heat-budget calculations for the rain areas showed an approximate balance between warm advection and adiabatic cooling at 850 mb, though diabatic heating was large above this level. For both depressions the region of maximum rainfall was coincident with the location of the maximum warm advection in the lower middle troposphere. In the suppressed northeast quadrant of both depressions subsidence warming was balanced by cold advection. Implications of this study's findings for eye formation in tropical storms and for improved satellite-imagery interpretation are discussed.