Arnold Sullivan: Investigating the Oceanic Feedback in ACCESS-CM2: A Heat Budget Analysis of May-June ENSO Dynamics
Investigating the mechanisms behind the weakened Bjerknes feedback in the ACCESS-CM2 climate model, which is associated with a biennial El Niño cycle, is essential important for the ENSO simulation in the climate model. Analysis of sea surface temperature (SST) correlation patterns reveals a significant decoupling between the Niño 3 and Niño 4 regions during the boreal spring/early summer (May - June) compared to observations. Through a leave-one-out mixed-layer heat budget analysis, we identify that the model’s central Pacific (Niño 4) variability is excessively dominated by surface heat flux (SHF) rather than ocean dynamics. This thermodynamic dominance in the central Pacific leads to a regime where ocean advection acts primarily to balance the strong SHF variance rather than driving seasonal SST growth, thereby severing the necessary zonal connection to the eastern Pacific for robust ENSO development.