The impact of the parameterization of heterogeneous vegetation on the modeled large-scale circulation in CCM3-BATS

This letter reports evidence of an unexpected large change in the planetary-scale circulation as a consequence of modifying the land cover within the Community Climate Model (CCM3). Three 10-year simulations were analyzed using (i) default land cover, i.e., a single dominant vegetation in each land grid cell; (ii) aggregate land cover that includes a representation of subpixel heterogeneity; and (iii) aggregate land cover for aerodynamic properties, but default land cover otherwise. Simulations (ii) and (iii) were similar, indicating that aerodynamic properties are influential at the planetary scale. Comparing these two runs with (i), there are significant differences in the boreal summer. These include a northward shift of the Northern Hemisphere jet that relates to a decrease in the zonally averaged aerodynamic roughness around 60 degrees N, and a perturbation of the Southern Hemisphere jet. Field significance tests suggest these changes are likely a remote influence of the Northern Hemisphere perturbation, not a sampling fluctuation.