Response of the Equatorial Pacific Ocean to A Uniform Energy Flux Forcing in A Fully Coupled Atmosphere-Ocean GCM

We study the response of the equatorial Pacific Ocean to a uniform heating using the fully coupled Community Earth System Model (CESM). The imposed heating induces an El Nino-like SST warming pattern over the equatorial Pacific. This is in contrast to the conventional ocean dynamical thermostat (ODT) based on the simplified coupled ocean-atmosphere model in which a heating of the tropics leads to a La Nina-like response. Similar to what happens in a majority of climate models with regard to future projections, the El Nino-like SST warming is accompanied with a slowdown of the Walker circulation, a reduction in sea level pressure across the equator, a weakening of the equatorial currents, and a shoaling of the thermocline in the western Pacific. The surface heat budget analyses are then performed to diagnose the mechanisms of the El Nino-like pattern formation. In response to the uniform heating, in addition, we find that there is a reduction in the amplitude of the seasonal cycle of SST in the equatorial Pacific. Results from an opposite scenario in which the model is forced with a uniform cooling will also be presented.