Energy Transports in an Idealized Moist GCM

We study changes in the meridional energy fluxes as the atmospheric moisture content is varied within an idealized general circulation model. The key elements of the model physics are gray radiative transfer and a mixed layer aquaplanet surface boundary condition. We vary the moisture content of the atmosphere from dry to ten times a control value by changing a constant in the Clausius-Clapeyron relation. The general circulation changes significantly as the moisture content changes: the dry static stability increases substantially in the midlatitudes and the jet moves poleward as moisture increases. However, despite the large changes in stability (which we interpret with the moist convection-controlled theory of Juckes 2000), eddy length scales in midlatitudes stay similar. Additionally although moisture fluxes increase significantly as moisture content is increased, there is a high degree of compensation by dry static energy fluxes, leaving the moist static energy fluxes approximately the same. We interpret this behavior with simplified models, including an energy balance model which has no change in flux as moisture is varied.