The Influence of Poloidal Motions and Latent Heat Release on the Equilibrium Ice Extent in a Simple Climate Model

Abstract

A zonal-average, annual-mean, statistical-dynamical climate model governing two domains (the atmosphere and a subsurface medium consisting of either ice or ?swamp?), and including the dynamics of mean poloidal motions and the hydrologic cycle as well as the ice-albedo feedback, is integrated numerically as a function of the solar constant. The adiabatic effect of the mean poloidal motion is to cool the system in the region of the ascending branch of the Ferrel cell (thereby promoting an advance of the equilibrium ice extent in this region) and to warm the system in the region of the descending branch (hence posing a ?barrier? to the ice advance in this region). This latter barrier effect is amplified as the solar constant is reduced because the subtropical descending motion increases in magnitude as the ice advances. The hydrologic non-adiabatic consequences of the mean poloidal motions tend to offset these adiabatic consequences to some degree. In general, the release of latent heat in middle and high latitudes associated with the poleward flux of water vapor reduces the equilibrium ice advance that would otherwise occur due to reductions in the solar constant.