Intraseasonal oscillations over tropical Indian ocean in relation to monsoon onset and rainfall events over the peninsular India

Abstract

Detailed analysis of the satellite derived water vapour for a five years period (1995-1999) prior to and during southwest monsoon is done over the Indian subcontinent and the adjoining seas. Three layer                     (1000 hPa –  700 hPa, 700 hPa –500 hPa  and 500 hPa -300 hPa) and total moisture data available from NOAA/TOVS satellite are used for the analysis. These data are used to study the northward propagating intraseasonal oscillations in the tropical Indian Ocean during the summer monsoon season. Results indicate the presence of intraseasonal oscillations in the middle    (700 hPa – 500 hPa) and the upper level (500 hPa – 300 hPa) water vapour. Wavelet analysis is applied to study the characteristics and time evolution of the intraseasonal oscillations especially over East Arabian Sea (EAS). Intraseasonal oscillations with periods ranging from 8-15 days, 15-30 and 30-60 days are seen over EAS. Heavy rainfall events over west coast of peninsular India are studied before and after the monsoon onset in terms of moisture availability in the middle level and zonal wind speed. The water vapour content and zonal wind speed over the Eastern Arabian Sea are found to influence rainfall over the west coast of India.