Transmission of ENSO signal to the Indian Ocean

The dynamics of El Nino-Southern Oscillation (ENSO) cycles has previously been interpreted in terms of discharge and recharge of mass and heat in the equatorial Pacific. Some of the ENSO discharge/recharge signals transmit into the Indian Ocean, but the pathway is yet to be fully established. This study reveals a previously un-noticed subtropical North Pacific (NP) pathway. NP Rossby waves associated with ENSO impinge on the western boundary and move equatorward along the "ray-path'' of Kelvin-Munk waves, and reflect as equatorial Kelvin waves. En-route to the equator, the waves are reinforced by wind stress anomalies associated with ENSO. The reflected equatorial Kelvin waves impinge on the Australasian continent and move poleward along the northern western Australia (WA) coast as coastally-trapped waves, radiating Rossby waves into the south Indian Ocean. In this way, some 55% of the total interannual variance of the WA thermocline is linked to the subtropical NP Rossby waves.