[A-CG43] Multi-scale ocean-atmosphere interaction in the tropics

[ACG43-10] The role of oceanic waves in transmitting the effect of reduced heat release in the Kuroshio Extension region to El Niño-like warming

*Taiki Kobayashi¹, Tomoki Tozuka¹ (1.The University of Tokyo)

Keywords:global warming, Pacific, balanced heat budget, sea surface temperature, thermocline, oceanic wave

The rate of ocean warming varies across different regions of the global ocean, but it remains unclear whether global warming leads to “El Niño-like warming”, with faster warming in the eastern equatorial Pacific, or the opposite “La Niña-like warming”. The projection of the warming pattern is important because this pattern may modulate radiative feedback to greenhouse gas forcing, the pace of global warming, and regional climate impacts. Although some hypotheses proposed so far have focused on tropical-extratropical interactions, the role of the Kuroshio Extension (KE) region has not received any attention. Since the Pacific absorbs the most heat in the eastern equatorial Pacific, while the KE region is the major heat release region, any changes in heat release over the KE region may be compensated by heat absorption in the eastern equatorial Pacific. To verify the possible role of this balanced heat budget, two sets of ensemble experiments are conducted with a regional ocean model configured for the Pacific. Specifically, the model is forced by atmospheric boundary conditions from a reanalysis product for the whole domain in the control runs. On the other hand, in the “+5°C experiments”, air temperatures at 10 m are artificially increased by 5°C only in the KE region to mimic the reduced heat release in this region under global warming. Compared to the control runs, the +5°C experiments show an increase in sea surface temperatures not only in the KE region but also in the eastern equatorial Pacific, where the prescribed atmospheric boundary conditions are unchanged. Additionally, to maintain a balanced heat budget by reducing heat absorption in the eastern equatorial Pacific, the equatorial thermocline deepens. This intriguing result suggests that a decrease in heat release in the KE region associated with global warming may promote an El Niño-like warming. Further analyses suggest that oceanic waves may play a crucial role in transmitting the effects of reduced heat release in the KE region.