Atmospheric Barotropic Energy Transfer Response to Global Warming

The projected changes in temperature due to global warming will have a profound effect on the behavior of midlatitude eddies. Using an idealized moist global circulation model the atmospheric barotropic energy balance is studied over a wide range of climates. This is done by applying the theoretical geostrophic turbulence picture that was realistically examined as a function of latitude in both atmospheric and oceanic reanalysis data. The barotropic energy cycle is found to shift poleward as the longwave optical thickness increases in concert with the poleward shift of the static stability, driven by the poleward shift of the upper-level baroclinicity. The baroclinic-barotropic conversion (barotropization) shows a non-monotonic behavior at midlatitudes as the climate becomes warmer, and reaches a maximum value around present-day climate and lower values at colder and warmer climates. This is found to be associated with the non-monotonic behavior of the stratification. Similar to the barotropization, the strength of the inverse energy cascade also shows a non-monotonic behavior as the climate becomes warmer. The inverse energy cascade, however, does not shift poleward, but rather corresponds to the uniform latitudinal distribution of the QG-supercriticality through all climates, and thus remains at the same latitudinal location. The eddy-mean flow interactions increase and transfer kinetic energy from the eddies to the mean flow, at low and high latitudes, and from the mean flow to the eddies, at midlatitudes, as the climate becomes warmer. This occurs mostly due to the decrease of the latitudinal extent of the mean flow at high latitudes, which increases and shifts equatorward the meridional shear of the barotropic mean zonal wind. The findings of this study imply that in future projected climates the eddy flow should have a more baroclinic nature, dominated by eddy-mean flow interactions.