On the role of convective systems over the northwest Pacific and monsoon activity over the Indian subcontinent

Abstract

The association between convective systems over the northwest Pacific (NWP) and monsoon activity over the Indian subcontinent has been studied for the period 1951-2003. It was found that no systems formed over the NWP region about 5 pentads prior to and 5 pentads after the monsoon onset over Kerala (MOK), southwest India. The characteristics of these convective systems such as frequency, geographical location, duration of the systems and the direction of movement of the systems over the NWP have been examined in relation to breaks in monsoon conditions over the Indian sub-continent during contrasting monsoon years. A see-saw nature of convection between the NWP and north Indian Ocean was found during the years with excess monsoon rainfall. It was also seen that the low level wind flow at 850 hPa was substantially more (less) and directed towards the Indian subcontinent (equatorial region) during the monsoon years that experienced a rainfall excess (deficit). It was found that in the deficit years and prolonged breaks in monsoon conditions, the majority of systems (about 69%) formed further south than in the case of excess monsoon years. The maximum difference in the shift of latitude (5.4°) and longitude (6.9°) was observed in the peak monsoon month of July indicating the significant influence of the convective systems over the northwest Pacific Ocean on the monsoon activity over the Indian subcontinent. This significant shift in the genesis of the cyclones over the NWP could be due to the shift in the low level jet. Copyright © 2009 Royal Meteorological Society.