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19 - Analysis of superpressure balloon trajectories and conventional observations over the Indian Ocean during different phases of the 1975 southwest monsoon

Published online by Cambridge University Press:  05 November 2011

D. Cadet
Affiliation:
Laboratoire de Météorologie Dynamique
P. Olory-Togbé
Affiliation:
Laboratoire de Météorologie Dynamique
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Summary

The trajectories of 45 superpressure balloons launched in the tropical boundary layer over the Indian Ocean during the 1975 summer monsoon are analysed in conjunction with conventional meteorological observations which consist mainly of ship reports. An assimilation of these randomly distributed data is performed to compute mean gridded fields (wind, pressure, air and sea-surface temperature) during four periods defined according to the level of monsoon activity over the Indian subcontinent. The main features of the southwest monsoon over the Indian Ocean are presented and discussed. More particularly, the differences in meteorological fields between the different periods are emphasized in order to determine the association between mean meteorological conditions over the Indian Ocean and monsoon activity over the subcontinent.

Introduction

Because of the lack of data over vast areas of the Indian Ocean, the details of the monsoonal airflow at low levels, where the development of the southwest monsoon takes place, still remains largely unknown.

All previous studies over the ocean have been related to monthly mean fields or local measurements, while transient phenomena of interest occurring with shorter periods over the Indian monsoon region as a whole are still largely uninvestigated. For example, one of the most important phenomena, which is the alternating of break and strong activity of the monsoon over the Indian subcontinent, takes place with a period of about two weeks. The study of the relationship between the variability of monsoon rainfall and that of the fields of other meteorological variables requires a knowledge of the variability of these fields averaged over a few days.

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Information
Monsoon Dynamics , pp. 287 - 308
Publisher: Cambridge University Press
Print publication year: 1981

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