Interhemispheric Asymmetry of Warming in an Eddy-Permitting Coupled Sector Model

Climate model projections and observations show a faster rate of warming in the Northern Hemisphere (NH) than the Southern Hemisphere (SH). This asymmetry is partly due to faster rates of warming over the land than the ocean, and partly due to the ocean circulation redistributing heat toward the NH. This study examines the interhemispheric warming asymmetry in an intermediate complexity coupled climate model with eddy-permitting (0.258) ocean resolution, and results are compared with a similar model with coarse (18) ocean resolution. Themodels use a pole-to-pole 608wide sector domain in the ocean and a 1208wide sector in the atmosphere, with Atlantic-like bathymetry and a simple land model. There is a larger high-latitude ocean temperature asymmetry in the 0.258model compared with the 18model, both in equilibrated control runs and in response to greenhousewarming. The larger warming asymmetry is caused by greatermelting of NH sea ice in the 0.258model, associatedwith faster, less viscous boundary currents transporting heat northward. The SH sea ice and heat transport response is relatively insensitive to the resolution change, since the eddy heat transport differences between themodels are small comparedwith themean flowheat transport.When awind shift and intensification is applied in these warming scenarios, the warming asymmetry is further enhanced, with greater upwelling of cool water in the Southern Ocean and enhanced warming in the NH. Surface air temperatures show a substantial but lesser degree of high-latitude warming asymmetry, reflecting the sea surface warming patterns over the ocean but warming more symmetrically over the land regions.