Impact of an Eddy-Permitting Ocean Resolution on Control and Climate Change Simulations with a Global Coupled GCM

Abstract

Initial results are presented from a 150-yr control and an 80-yr transient simulation of a new global coupled climate model with an ocean model resolution of ?°, which is sufficient to permit ocean eddies to form. With no spinup procedure or flux correction, the coupled model remains close to radiative equilibrium, and the enhanced ocean resolution allows an improved ocean state to be simulated; this includes a general decrease in sea surface temperature errors compared to climatology and more realistic large-scale flows compared to previous lower-resolution models. However, the improvements in the atmospheric and coupled model climatology are less pronounced, with small improvements in atmospheric circulation counterbalanced by an El Niño?Southern Oscillation cycle that has peak power at too short a period and with too little power on longer time scales. With the model using exactly the same atmospheric component as a lower-resolution counterpart, the comparison gives some insight into the impact of ocean resolution on climate and suggests that a corresponding increase in atmospheric resolution may be needed before major changes to the coupled climatology are seen. The transient climate change simulation shows some important regional differences in response compared to previous lower-resolution models. A less pronounced weakening to the meridional overturning in the North Atlantic leads to a smaller decrease in northward heat transport and enhances the surface temperature increase in the northern Europe?Atlantic region by 10% over the lower-resolution model. This may be connected to processes involved in deep-water formation in the Labrador and Nordic Seas.