The Role of Moist Baroclinic Instability in the Growth and Structure of Monsoon Depressions

J. A. Aravequia Instituto Nacional de Pesquisas Espaciais, São José dos Campos, Sao Paulo, Brazil

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V. Brahmananda Rao Instituto Nacional de Pesquisas Espaciais, São José dos Campos, Sao Paulo, Brazil

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J. P. Bonatti Instituto Nacional de Pesquisas Espaciais, São José dos Campos, Sao Paulo, Brazil

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Abstract

The effect of latent heat of condensation on baroclinic instability process is studied using the model developed by Bonatti and Rao. This model includes the effect of latent heat of condensation as parameterized by Mak, a zonal wind profile that varies linearly with pressure, and a constant lapse rate of −6°C km−1. The effect of dissipative terms and vertical variation of heating on baroclinic instability with positive and negative zonal wind shears is studied.

Dissipative terms and the type and intensity of heating change the selection of the most unstable wave. Viscosity and Newtonian cooling stabilize short waves. The characteristics of the most unstable wave obtained using a double maximum in the vertical distribution of heating and observed vertical profiles of zonal wind and temperature representative of the summer monsoon of India resemble those of observed monsoon depressions. The inclusion of dissipative effects makes the Green mode the most unstable wave.

Abstract

The effect of latent heat of condensation on baroclinic instability process is studied using the model developed by Bonatti and Rao. This model includes the effect of latent heat of condensation as parameterized by Mak, a zonal wind profile that varies linearly with pressure, and a constant lapse rate of −6°C km−1. The effect of dissipative terms and vertical variation of heating on baroclinic instability with positive and negative zonal wind shears is studied.

Dissipative terms and the type and intensity of heating change the selection of the most unstable wave. Viscosity and Newtonian cooling stabilize short waves. The characteristics of the most unstable wave obtained using a double maximum in the vertical distribution of heating and observed vertical profiles of zonal wind and temperature representative of the summer monsoon of India resemble those of observed monsoon depressions. The inclusion of dissipative effects makes the Green mode the most unstable wave.

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