The Dependence of Deep Cloud Mass Flux and Area Cover on Convective and Large-Scale Processes

G. S. Bhat Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore, India

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Abstract

A framework has been developed that brings together the important physical parameters and processes governing the vertical mass flux in deep convective clouds and their area cover. The main result is a simple relation for the cloud mass flux and area fraction in terms of the large-scale radiative cooling, environmental stratification, and the extent of lateral entrainment of the ambient air by the convective systems. It is shown that the contribution of the moist processes to the total vertical mass flux in deep clouds can become comparable to that of the large-scale radiative component, and thus the neglect of these subsynoptic-scale processes can severely underestimate the convective activity. Further, it is argued that the consideration of moist processes is not merely a question of the inclusion of a correction factor in the relationship, but the uncertainty that needs to be overcome before meaningful predictions of deep cloud area cover can be achieved.

Corresponding author address: Dr. G. S. Bhat, Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore 560012, India.

Email: bhat@caos.iisc.ernet.in

Abstract

A framework has been developed that brings together the important physical parameters and processes governing the vertical mass flux in deep convective clouds and their area cover. The main result is a simple relation for the cloud mass flux and area fraction in terms of the large-scale radiative cooling, environmental stratification, and the extent of lateral entrainment of the ambient air by the convective systems. It is shown that the contribution of the moist processes to the total vertical mass flux in deep clouds can become comparable to that of the large-scale radiative component, and thus the neglect of these subsynoptic-scale processes can severely underestimate the convective activity. Further, it is argued that the consideration of moist processes is not merely a question of the inclusion of a correction factor in the relationship, but the uncertainty that needs to be overcome before meaningful predictions of deep cloud area cover can be achieved.

Corresponding author address: Dr. G. S. Bhat, Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore 560012, India.

Email: bhat@caos.iisc.ernet.in

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