Self-maintaining Eddy-driven Jets

Abstract

For the purposes of this talk, a jet is self maintaining if its zonal winds, both barotropic and baroclinic, are stronger than they would be in the absence of eddies. It appears that Earth's wintertime midlatitude jets are self maintaining. This has implications for annular variability: both intrinsic (annular modes) and that driven from the tropics (annular response to ENSO).

The dynamics of self-maintaining jets are explored using the quasi-geostrophic theory of eddy-zonal flow interactions and a simple numerical model. We focus on the abrupt emergence of a self-maintaining jet as the radiative-equilibrium equator-pole temperature contrast is increased. This abrupt transition is induced by multiple positive feedbacks, involving shifts in critical latitudes, the suppression of baroclinic instability by barotropic shear, and the enhancement of baroclinic instability by baroclinic shear.