[A-CG33] Multi-scale ocean-atmosphere interaction in the tropics

[ACG33-P06] El Niño-like warming associated with reduced heat release in the Kuroshio Extension region

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

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

The rate of ocean warming is known to vary across different regions of the global ocean. However, it is still not clear whether “El Niño-like warming” with faster warming in the eastern equatorial Pacific or the opposite “La Niña-like warming” occurs under global warming. Although most hypotheses proposed so far have focused on processes in the tropics, it is possible that the Kuroshio Extension (KE) region affects the eastern equatorial Pacific through a balanced heat budget. 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 this possibility, two 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 run, whereas air temperatures are artificially increased by 5°C only in the KE region in the “+5°C experiment” to mimic the reduced heat release in this region as a result of global warming. Compared to the control run, the +5°C experiment shows an increase in SSTs not only in the KE region, but also in the eastern equatorial Pacific, where the atmospheric boundary conditions are not altered. 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 support a theoretical consideration that the equatorial thermocline becomes deeper to realize reduced heat absorption in the eastern equatorial Pacific.