A qualitative model of storm tracks

A simple heuristic model of the longitudinal structure of eddy statistics in the midlatitude storm tracks is described. The model consists of two interacting parts: a pseudo-energy budget for waves on an upper tropospheric PV contour; and low-level horizontal diffusion of temperature. The resulting low level heat flux provides the source of wave activity for the upper level waves, while the RMS of streamfunction variance in the wave field acts as the diffusivity for the low level heat transport. The source of wave activity is balanced by a sink determined by a zonally varying "holding capacity" that is a function of jet strength. A connection is also made with homogeneous turbulence theories for eddy diffusivities in baroclinically unstable flows by relating the strength of the PV jump across the contour to the eddy length scale.