A note on the contributions of mean and eddy terms to the momentum and heat balances of the troposphere and lower stratosphere

Abstract

AbstractThe space‐time averaged zonal wind equation has been used in a two dimensional model to infer the mean meridional circulation of the Northern Hemisphere upper troposphere and lower stratosphere at the solstices. A three cell system is found with maximum meridional speed of 120 cm sec−1 in winter and 40 cm sec−1 in summer and vertical speeds of 0.3 cm sec−1 in winter and 0.1 cm sec−1 in summer. The lower stratosphere circulation shows a continuation of the tropospheric cells with speeds decreasing with height.Using these results together with estimates of the eddy convergence terms and the ‘diabatic’ contributions based on values obtained from the literature the component terms in the zonal momentum and heat budgets are listed. In the former, in agreement with other workers, the main balance is between the convergence of the horizontal eddy flux and the mean meridional flow (Coriolis torque) terms. In the latter the balance is principally between the ‘diabatic’ term, the (subsidence) term due to the mean vertical flow and both the horizontal and vertical eddy heat flux convergence terms.The limitations of the data on which the calculations are based are emphasized and estimations of the consequent uncertainties in the results are obtained by repeating the computations with different input data. In particular no measurements are available of the term due to the convergence of the vertical eddy flux of momentum. Most authors have assumed it to be zero but calculations have also been made here using values based on results given by Smagorinsky, Manabe and Holloway (1965) for their 9‐level general circulation model experiments.