Sensitivity to the vertical and meridional structure of the meridional temperature gradient in a three-layer quasigeostrophic turbulence model

To gain a better understanding of the possible response of atmospheric circulation to climate change, we explore the sensitivity of statistically-steady three-layer quasigeostrophic (QG) turbulence on a beta-plane to model parameters. In a warmer climate, one would expect a larger meridional temperature gradient in the upper-troposphere due to moist convection in the tropics, and a smaller temperature gradient in the lower-troposphere due to polar amplification. The three-layer QG model is the simplest that allows for different upper- and lower-level temperature gradients, set through imposed vertical shear across the two interfaces.

Past work with three-layer models has focused on the vertical structure of the potential vorticity flux, in the horizontally homogeneous case (Held and O'Brien, 1992, J. Atmos. Sci., 49, 1861-1870) as well as in the case of a narrow meridionally-localized baroclinicity (Pavan, 1996, Q. J. R. Meteorol. Soc., 122, 55-72). Pavan also began to explore the sensitivity of momentum-flux convergence to vertical resolution without exploring the behavior of the three-layer momentum fluxes in detail. We focus on the three-layer model, and vary not only the vertical structure, but also investigate the importance of the width of the baroclinic zone. We present results on the sensitivity of eddy momentum flux and associated surface winds to both the meridional and the vertical structure of the equilibrium temperature gradient.