Equatorial Rossby waves and their impacts on monsoon region deep convection

Abstract

Convectively coupled equatorial Rossby waves are the dominant mode of westward-moving subseasonal convection in the tropics. A portion of the variance in these waves has been shown to associate with the tropical intraseasonal oscillation, along with a process often mediated by the extratropical Rossby wave response to tropical convection that yields Rossby waves breaking back into the tropical atmosphere. The potential vorticity anomalies driven by Rossby wave breaking become the equatorial Rossby waves. This work creates an index of planetary scale equatorial Rossby waves and applies the method of seasonally varying regression slope coefficients to diagnose their preferred associations with tropical and extratropical circulation features. Results confirm the already known association between these waves and the extratropical atmosphere and they reveal a pattern of westward-and northward-moving anomalies of tropical convection over the Indian Ocean and Southern Asia during the Northern Hemisphere summer. These patterns are associated with a cycle of suppression and enhancement of convection in which negative anomalies of outgoing longwave radiation are found to be 3-times as likely during the wet than the dry phases of the waves.