Migration of atmospheric convection coupled with ocean currents pushes El Nino to extremes

Abstract

The warm phase of El Nino-Southern Oscillation can grow much stronger than the cold phase, but the associated dynamics are not well understood. Here we show that the anomalous zonal advection of warm water is the major process that pushes El Nino to extremes and that this anomalous advection results from the coupling of oceanic currents with eastward migration of the atmospheric convection; a greater zonal advection is associated with a greater extent of the eastward migration. By contrast, there is a limited extent for westward migration during La Nina. Climate models that successfully simulate the amplitude asymmetry display a systematic linkage of a greater longitudinal movement of the convection center with a stronger zonal advection and greater El Nino amplitude. In a warming world, the longitudinal migration of convection response increases, as does the role of zonal advection, increasing the frequency of future extremes of El Nino.