THERMALLY FORCED STATIONARY AXISYMMETRICAL FLOW ON THE F-PLANE IN A NEARLY FRICTIONLESS ATMOSPHERE

This paper investigates stationary axisymmetric balanced flow of a sta bly stratified dry non-Boussinesq atmosphere on the f plane. The circu lation is forced in the troposphere through thermal relaxation toward a specified equilibrium temperature and is damped through Rayleigh fri ction in the interior of the domain. Surface friction is sufficiently strong to ensure weak surface winds. As in the analogous zonally symme tric problem studied by Plumb and Hou there is threshold behavior in t he frictionless limit with a thermal equilibrium solution for subcriti cal forcing and a highly nonlinear so-called angular momentum conservi ng (AMC) solution for supercritical forcing. The latter is characteriz ed by a sharp outward edge of the vortex circulation and a nonvanishin g secondary cross-vortex circulation. In the frictionless limit, the s econdary circulation does not reach above the region of the thermal fo rcing. Noticeable differences of the current problem with respect to t he zonally symmetric problem arise from the strong nonlinearity of the thermal wind equation and the nonzero thermal forcing right on the ax is of symmetry. For the highly nonlinear AMC solution an approximate a nalytical theory is presented and verified by use of a numerical Elias sen balanced vortex model. This model is also used to investigate the nonlinear dependence of the secondary circulation on the Rayleigh fric tion coefficient and the penetration of the secondary circulation abov e the tropopause. An analytic Green's function solution for the linear ized problem gives insight into nonlinear asymptotic dependences. Thin king in terms of an Eliassen balanced vortex model offers a new view o n the secondary circulation in the AMC regime.