ENSO influence on freshwater and heat budgets in the Tropical Pacific Ocean state estimate

Abstract:

A 1/3° regional state estimate assimilating components of the Tropical Pacific Observing System (TPOS) was constructed for 2010 through 2018. The evolving ocean state is consistent with the model dynamics and observations, making the simulation useful for analyzing the ocean variability through the 2015-2016 El Niño event. We document changes to stratification, the undercurrent, and upwelling structure during this period. Freshwater and heat budgets are analyzed between 5°S and 5°N in the upper 300 m to understand the bulk ocean evolution. Vertical mixing across 300 m is negligible, meaning property changes are balanced by horizontal and vertical advective divergence and surface forcing. Warming during the El Niño is driven primarily by anomalies in vertical advection, while freshening is driven by anomalies in horizontal advection. Vertical advection also drives the recovery in temperature, though surface fluxes are also important in the relaxation from El Niño conditions. For the freshwater budget, all terms contribute to the relaxation from El Niño conditions. Significant lagged correlations to the Niño 3.4 index are found for most budget terms, with some terms leading and others lagging the index.