The Effect of the Meridional Circulation on the Baroclinic Instability of the Winter Zonal Flow

Abstract

The linear instability of the observed winter zonal mean flow, with and without the inclusion of the meridional circulation, is presented. The purpose of this note is to determine whether the meridional circulation has an important effect on the growth-rate spectrum and structure of the linear baroclinic waves. It is found that the inclusion of the meridional circulation produced only slight changes in the growth-rate spectrum, as compared to the case where the meridional flow is neglected. The presence of the meridional flow destabilized all wavenumbers greater than 5, although the change was less than 7% for all wavenumbers. The maximum growth rate, with or without considering meridional circulation, occurred between wavenumbers 12 and 15. The wave structures were also very similar in the two cases. The maximum amplitude of the geopotential perturbation for wavenumbers 5?7 remains at the earth?s surface when the meridional circulation is included; however, the position of the maximum geopotential perturbation at the earth?s surface is displaced northward about 250 km.