An asymmetric mode of tropical Indian Ocean rainfall variability in boreal spring

An analysis of observational estimates has revealed an asymmetric mode of boreal spring rainfall and wind variability over the tropical Indian Ocean. The asymmetric mode is characterized by opposite rainfall and surface wind anomalies north and south of the equator. This mode is associated with a cross-equatorial gradient in sea surface temperature anomalies. The evolution of this mode is related to air-sea interactions in the tropical Indian Ocean. In particular, surface heat fluxes play an important role in the initiation, development, and decay of this mode. The occurrence of this mode in observations is closely linked to both El Nino-Southern Oscillation (ENSO) and the Indian Ocean Dipole mode. Coupled general circulation model experiments indicate that this mode can occur in the absence of ENSO. The variability associated with this mode enhances ENSO's teleconnection to the Indian Ocean and affects the seasonal transition in the tropical Indian Ocean.