Equilibration of a Simple Baroclinic Flow in aβChannel and on the Sphere

Abstract

Abstract The statistical equilibration of baroclinic waves in a two-level quasigeostrophic model subject to forcing and dissipation is studied. The model employed may be formulated in either spherical or Cartesian geometry and is restricted to a midlatitude channel. Parameters are chosen so that only up to three waves can become supercritical (one planetary- and two synoptic-scale waves). It is found that both geometries exhibit essentially two equilibration regimes as the forcing temperature gradient varies. At low forcing, the planetary-scale wave is not excited while the two synoptic-scale waves equilibrate with steady finite amplitude. In this regime, the equilibrated temperature gradient is sensitive to forcing; the authors argue that this is due to the barotropic governor effect. At higher forcing, the planetary wave becomes active and the solution is aperiodic. In this regime, the planetary wave acts to reduce the barotropic shear spun up by the synoptic waves, thereby limiting the role of the baro...