E3SM’s Sensitivity to ocean heat transports strength: A slab ocean model study
The sensitivity of the Energy Exascale Earth System Model version 2 (E3SMv2) baseline climate to ocean heat transport (OHT) strengths is examined using a series of E3SMv2 Slab Ocean Model (SOM) experiments. SOM experiments are forced with prescribed ocean heat convergences derived from fully coupled experiments with realistic/weak ocean circulation strengths. The results indicate that E3SMv2 has a large surface temperature sensitivity to OHT strengths, with a global surface temperature difference of about 4.0°C between high-/low-OHT experiments. The surface temperature response occurs mainly over the subpolar regions in both hemispheres, due to the ocean heat convergence pattern which diverges/converges heat over the tropical/subpolar regions. However, the surface temperature sensitivity to high/low-OHT forcing is greater in the Southern Ocean than in the Northern Hemisphere. This large Southern Ocean sensitivity is associated with an overcompensation between the prescribed OHTs and the atmosphere heat transport response, due to the impact of shortwave cloud radiative effect in enhancing the surface temperature response. The positive/negative shortwave cloud radiative effect is caused by mid-latitude marine low-level clouds' decrease/increase response to high/low OHT forcing. Results suggest a relatively stronger mid-latitude cloud feedback in E3SM.