The benefits of high-resolution models in simulating the Kuroshio Extension and its long-term changes

The Kuroshio Extension (KE) is a narrow midlatitude zonally oceanic jet-like flow, characterized by abundant mesoscale eddies and intense air–sea interaction with significant impact on the North Pacific storm track. Using two sets of coupled model simulations with FGOALS and HadGEM3, this paper evaluates the benefits of high-resolution models in simulating the climatological structure of the KE and its historical warming trend, by comparing high-resolution with low-resolution simulations from the same model. It is found that high-resolution models consistently improve the simulated KE intensity and enhanced warming trend. In low-resolution models, the warming is centered more northernly (around 40° N) and shallower (about 300 m) compared to observations (around 35° N). In high-resolution simulations the warming is much more concentrated, located around 35° N with two warming centres in the vertical, one near the surface and one in the subsurface. Decadal temperature changes mainly reflect positional KE shifts, with northward movement resulting in a warming and southward movement resulting in cooling. Heat budget analysis shows the temperature advection term was the major contributor to the Kuroshio Extension enhanced warming, suggesting a possible intensification of the western boundary circulation.