Tropopause Height in Baroclinic Channel Flow

A wave–mean flow model of dry channel flow is used to investigate the processes that determine the height HT and the slope of the extratropical tropopause. Without baroclinic waves, differential radiative heating and a convective adjustment mechanism cooperate to establish a well-defined tropopause and a mean zonal wind with almost constant vertical shear. This reference state is neutrally stratified in the troposphere and, therefore, baroclinically unstable. It is shown that the meridional and vertical heat transports by the unstable linear eigenmodes induce a rise of the tropopause in the northern part of the channel, whereas there is little change of HT in the south. These predictions of the linear theory are verified by aid of the nonlinear model. Changes of HT are restricted to the jet region if a jet is enforced.