Changes in Cross-Equatorial Ocean Heat Transport Impact Regional Climate and Precipitation Sensitivity




Oghenechovwen, Oghenekevwe C.

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Do changes in how cross-equatorial energy transport is partitioned between the ocean and atmosphere impact the hemispheric climate response to forcing? To find out, we alter the cross-equatorial ocean heat transport in a state-of-the-art GCM and ascertain how changes in energy transport and its partitioning impact hemispheric climate and precipitation sensitivity following abrupt CO2-doubling. We further evaluate the applicability our results in CMIP6-class ESMs, where AMOC facilitates the northward cross-equatorial ocean heat transport. In our experiments, changes in ocean cross-equatorial energy transport trigger compensating changes in atmospheric energy transport through changes in the Hadley cells and a shift in the Intertropical Convergence Zone. However, the climate sensitivity in each hemisphere is linearly related to the ocean heat transport convergence, not atmospheric energy transport convergence, due to the impact of ocean heating on evaporation and atmospheric specific humidity. Similarly, we also find that ocean heat transport convergence controls the hemispheric precipitation sensitivity through the impact of ocean heating on surface evaporation. This relationship is also evident in CMIP6 models, where we find differences in hemispheric precipitation sensitivity to be related to the Atlantic Meridional Overturning Circulation (AMOC). Changes in the AMOC control hemispheric differences in upper ocean heat content, which then affect how the hydrologic cycle responds to CO2 forcing in each hemisphere. These results suggest that ocean dynamics impact the hemispheric climate response to CO2 forcing, particularly how much regional precipitation changes with warming.



CMIP6, Atlantic Meridional Overturning Circulation, Energy Transport, Climate impacts, Climate change, Regional climate, Earth System Models, Community Earth System Model, Radiative Feedbacks, Cross-Equatorial Ocean Heat Transport, Precipitation Sensitivity, Hydrologic Sensitivity, Hydrologic Cycle, Intertropical Convergence Zone, Hadley Cells, Forcing, Atmosphere-ocean interaction, Coupled Climate Dynamics, Hemispheric climate response, Bjerknes compensation, Energy Transport Partitioning