18 - Determination of cloud cluster properties from MONSOON-77 data

Summary

The spectral diagnostic method based on the Arakawa–Schubert parameterization theory is applied to a case study of the active monsoon at the time of onset. The estimates of vertical mass flux, the vertical eddy transport of heat, the excess of temperature, the apparent heat source and the apparent moisture sink are found to be much higher than those for disturbed conditions in the equatorial Pacific. Conditional instability of the second kind (CISK) appears to be operative in the presence of a large vertical mass flux associated with shallow clouds.

Introduction

Precipitation during the Indian southwest monsoon is in the form of thundershowers, showers, or rain. The presence of cumulus and cumulonimbus clouds over the Arabian Sea during the active monsoon has been noted by several authors (Deshpande, 1964; Bunker and ChafTe, 1969). General-circulation studies (Manabe et al., 1970) have verified the importance for the intensification of the monsoon circulation of the release of latent heat by convection in the ascending air. In recent years the interaction between cumulus-scale convection and large-scale motion has been the subject of several theoretical and diagnostic studies. A spectral diagnostic method has been developed on the basis of the parameterization theory formulated by Arakawa and Schubert (1974) and used by Cho and Ogura (1974) for the study of composite data of easterly waves, by Nitta (1975) for the Barbados Oceanographic and Meteorological Experiment (BOMEX) phase III data, and by Yanai et al. (1976) for the intertropical convergence zone (ITCZ) Marshall Islands data.