The Northern Hemisphere Wintertime Storm Track Simulated in the High-Resolution Community Earth System Model

With a pair of high-resolution (HR, 10 km ocean and 25 km atm) and low-resolution (LR, 100 km ocean and 100 km atm) Community Earth System Model (CESM) simulations, we investigate and compare the long-term mean Northern Hemisphere (NH) wintertime storm tracks against reanalysis data. Based on several Eulerian measures, the CESM-HR shows a poleward shift of the NH storm tracks and a reduced equatorward bias in the North Pacific relative to the CESM-LR. Those may be associated with the refined topography of the Tibetan Plateau as well as the improved subtropical jet, stationary planetary waves, atmospheric baroclinity, and baroclinic energy conversion over the North Pacific. We also find that sharper oceanic fronts along the Kuroshio Extension accompanied by enhanced local atmospheric baroclinity and strengthened eddy heat flux over the northern North Pacific could be related to those improvements. Nevertheless, the North Atlantic storm track in HR is placed too north, leading to a larger negative bias over the subtropical zone than in LR. The simulated insufficient subtropical sensible and latent heat fluxes and northward zonal winds in HR seemingly coincide with the deficits in the North Atlantic storm track. The stronger NH branch of the Hadley cell and its poleward expansion in HR may be linked to the changes in the tropical precipitation and the poleward shift of the NH storm tracks. Further studies of attributing these biases to a specific aspect of the climate model by sensitivity experiments are warranted for further clarification of the mechanisms.