Dipole Structure of Mixed Layer Salinity in Response to El Nino-La Nina Asymmetry in the Tropical Pacific

The asymmetry of mixed layer salinity (MLS) anomalies in response to El Nino and La Nina events in the tropical Pacific is examined for the first time based on Argo observations and Estimating the Circulation and Climate of the Ocean simulation. The difference of MLS anomalies between El Nino and La Nina shows a dipole structure, with El Nino featuring strong negative salinity anomalies east of 160 degrees E while La Nina shows remarkable positive salinity anomalies west of 160 degrees E. A salinity budget analysis suggests that nonlinear zonal advection plays a dominant role in generating the asymmetric MLS structure. This dipole MLS structure acts to generate a dipole structure of barrier layer thickness and thus likely plays an important role in the development of El Nino-Southern Oscillation asymmetries in sea surface temperature.