THE FEEDBACK OF MIDLATITUDE WAVES ONTO THE HADLEY-CELL IN A SIMPLE GENERAL-CIRCULATION MODEL

We present self-consistent comparisons of axissymmetric and 3-dimensio nal simulations of the tropospheric circulation under idealized physic al conditions. These reveal a feedback of transient eddies onto the Ha dley circulation which, first, strongly depends on equatorial heating and, second, is in case of realistic heating quite different from pres cribed eddy forcing. A quantitative estimation for the eddy-induced mi xing of vorticity into the poleward flow of the Hadley cell is given. The proposed relation is in accordance with observations, It is derive d from the computational result that eddy momentum flux convergence is of the same order as the equatorward dux of relative vorticity genera ted by the Hadley circulation. Evaluation of the local budgets of sens ible heat gives rise to a clear picture of how the poleward heat trans ports due to Hadley circulation and transient eddies interlock. This m echanism is found to be essential for an interpretation of the eddy fe edback.