Abstract
Tropical Instability Waves (TIWs) are oceanic features that form around the equatorial Pacific cold tongue and influence the large-scale circulation and coupled climate variability including the El Niño-Southern Oscillation. Local air-sea coupling over TIWs is thought to play an important role in the atmosphere and ocean’s energy and tracer budgets, but is not well captured in coarse-resolution models. In this study we isolate the impacts of TIW thermal (sea surface temperature-driven) and current (surface current-driven) feedbacks by removing TIW signatures in air-sea coupling fields in a high-resolution regional coupled model. The thermal feedback is found to damp TIW temperature variance by a factor of two, associated both with the direct dependence of surface heat fluxes on SST (~74%) and indirect impacts on surface winds (~35%), air temperature and humidity (~−9%). These changes lead to cooling of the cold tongue SST by up to 0.1°C through reduced TIW-driven meridional heat fluxes, and associated small changes in atmospheric circulation. The current feedback is decomposed into TIW (i.e. mesoscale) and mean (i.e. large-scale) components using separate experiments, with both having distinct impacts on TIWs and the mean state. The mesoscale current feedback reduces TIW eddy kinetic energy (EKE) by 22% through the eddy wind work, while the mean current feedback induces a further reduction of 8% by extracting energy from the mean currents and thus reducing barotropic EKE shear production. An improved understanding of small-scale tropical Pacific processes is needed to address biases in coarse-resolution models that impact their predictions and projections of Pacific climate variability and change.
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