Alex Megann, Adrian New, and Bablu Sinha, NOC, Southampton
The CHIME (Coupled Hadley-Isopycnic Model Experiment) model comprises the Hadley Centre's atmosphere and ice models, coupled to HYCOM. CHIME is designed to be identical to the Hadley Centre's HadCM3 model except for its ocean component, allowing us to investigate the sensitivity of the climate to the choice of vertical coordinate in the ocean model.
A 120-year integration of CHIME with pre-industrial greenhouse forcing is now complete. Although the meridional overturning in the two models is similar, CHIME shows several differences compared with HadCM3. The meridional heat transports are stronger in CHIME although these, as well as those in HadCM3, fall within observational bounds. The path of the North Atlantic Current is more realistic than that in HadCM3, removing the heat flux errors in the subpolar gyre seen in the latter. CHIME does not show the 4K cold bias seen in the North Pacific in HadCM3, instead having a warm bias of comparable amplitude. These differences can be traced to differences in the strength and separation positions of the Kuroshio and its extension.