Abstract
The roles of eddy and zonal mean processes in producing the earth's annual-mean zonally-averaged tropospheric wind and temperature fields are investigated using a numerical zonally-averaged atmospheric model. First a diagnostic calculation is performed to determine the beat sources and sinks and mean meridional circulation which maintain the observed annual and zonal mean temperatures and surface zonal winds, given that all zonal momentum sources except those due to the zonal-mean motions are observed or parameterized. The use of observed data and calculations of the zonally-averaged radiative heat sources and sinks, together with some simplifying assumptions, permits estimation of the surface sensible heating atmospheric latent heating, and vertical eddy sensible heat flux divergences. Then the heat and momentum sources and sinks are varied (longwave radiation is taken to depend on the zonal mean temperature), and the steady state response of the zonal winds, temperatures, and meridional circulation to the altered forcing is found. Among the more interesting results are:
As long as there is sufficient internal friction for a steady state to exist, the Hadley circulation mass flux does not respond strongly to changes in the strength of the horizontal eddy momentum flux forcing, but does respond strongly to changes in the distribution of the tropical thermal forcing.
The response to varying the width but not the total precipitation of the intertropical convergence zone, with fixed eddy fluxes and extratropical heat sources, bears some resemblance to the observed zonally-averaged El Niño changes.
Given fixed latent and eddy heat sources, the horizontal eddy momentum fluxes are varied. The minimum speed of the jet stream is found in the reference state.
