The macroturbulence of the troposphere

Abstract

Eddy length scales, eddy velocity scales, and the amplitude of eddy fluxes in the mid-latitudetroposphere are discussed, primarily from the qualitative perspective provided by studies ofquasi-geostrophic turbulence. The utility of a diffusive picture for the near surface polewardflux of heat is emphasized, as is the extent to which a full closure theory for the troposphere,including the interior potential vorticity fluxes, must revolve around this theory for the heatflux. A central problem in general circulation theory is then to determine which factors controlthe horizontal diffusivity near the surface. The baroclinic eddy production problem has distinctivefeatures that make it stand out from other inhomogeneous turbulence problems such asBenard convection and laboratory shear flows, the crucial point being that there can be scaleseparation between the eddies and the scale of the mean flow inhomogeneity in the directionof the relevant transport. This scale separation makes diffusive closures more compelling. Inaddition, it allows one to compute diffusivities from models of homogeneous turbulence.