Studies on the regional characteristics of surface fields over the Indian Ocean and monsoon rainfall

Abstract

This paper investigates the regional characteristics of the surface fields in the tropical Indian Ocean and their relationship with the regional scale monsoon rainfall over India. Daily uninitialized ECMWF model analyses, NCEP re-analyses, COADS climatology of observations and rainfall data over 29 meteorological subdivisions of India are used in the present study. The study reveals that wind stress and latent heat flux exhibit zones of maxima over (i) Arabian Sea, (ii) Bay of Bengal, (iii) South China Sea and (iv) South Indian Ocean. In most of the surface fields, Arabian Sea figures as the most prominent region with its distinct regionality and variability. Specific regions with exactly opposite pattern of wind stress anomalies during below normal and normal/above normal monsoon appear in the North Indian Seas and in the South Indian Ocean and are believed to be the key regions as regards to monsoon variability. Coherence of the surface fields between one regional domain and the other, and their phase propagation within the regional domains are examined. Results suggest highly incoherent fluctuations of the surface fields in the semi-annual and seasonal bands and in all regional domains. Specific propagating trends with lead/lag relationship are revealed. Based on statistical studies, the potential of certain surface fields in specific regional domains for the prediction of rain fall over certain homogeneous zones of India are discussed.