Upper vs lower level baroclinicity: a QG study of storm track latitude

An interesting question that arises in multiple contexts is the extent to which baroclinic storm tracks are most strongly constrained by the lower tropospheric or upper tropospheric baroclinicity. This issue arises in discussions of the poleward displacement of jets and storm tracks associated with the ozone hole in the Southern Hemisphere as well as in response to global warming. Here we present results from the simplest model of a storm track in which the separate roles of upper level and lower level baroclinicity are distinguishable, a three-layer QG model.

We start with a simple thermal forcing in which upper level and lower level temperature gradients are forced by relaxation to a "radiative equilibrium" in which the latitude of the maximum forced temperature gradient is identical in the two temperature equations. We then systematically displace the latitude of the upper level forced baroclinicity from than in the lower level. In the regime that we focus on here, the storm track does not split and the resulting jet is equivalent barotropic, so we can unambiguously define a storm track displacement. We do not have a simple theory that explains our results, but hope that a description of these numerical simulations focuses attention on this basic question.