Testing a theory for the effect of latitude on the persistence of eddy-driven jets using CMIP3 simulations

The effect of latitude on the persistence of north-south shifts in the position of the jet is investigated in 37 CMIP3 integrations over four forcing scenarios. The persistence of the Southern Annular Mode (SAM) decreases when the mean jet is located closer to the pole. An asymmetry is shown whereby the equatorward-shifted jet is more persistent than the poleward-shifted jet. The sphericity of the earth inhibits wave breaking on the poleward flank of the jet which decreases the feedback between the eddies and the mean-flow and yields a wider, less self-sustaining jet. The results suggest a decrease in e-folding time of the SAM of 3 days per degree of poleward shift of the jet. The mechanism described explains why models with jets too far equatorward relative to observations over-predict the timescale of the SAM and suggests that these models will also exaggerate poleward shifts of jets associated with global warming. Citation: Barnes, E. A., and D. L. Hartmann (2010), Testing a theory for the effect of latitude on the persistence of eddy-driven jets using CMIP3 simulations, Geophys. Res. Lett., 37, L15801, doi: 10.1029/2010GL044144.