Convective and boundary layer parametrizations in a diagnostic model of atmospheric fronts

Abstract

Numerical integrations of initial value problems and observations have shown that along-front geostrophy is a good approximation in frontal regions, even in the presence of strong frontogenetic forcing. Consequently the cross-frontal circulation equation described by A. Eliassen in 1961 is a powerful diagnostic tool. Extra terms have been added to represent parametrized convective and boundary layer physics. The inclusion of cumulus heating modelled on that used in CISK theories produces bands of ascent whose scale decreases as the heating amplitude increases. For realistic cold fronts bands are produced just ahead of and behind the surface temperature contrast depending on the type of frontogenetic forcing. The application of this convective parametrization to finite amplitude circulations about a front is rather different from previous uses in theories of CISK. The solution method makes it simple to examine a much larger class of representations, hence providing a fresh appraisal of the parametrizations. The integrated frontogenetic tendency is calculated in the frame of reference moving with the front for the various cases considered. This allows discussion of the notion of a steady state front and indicates the crucial role of convective and boundary layer processes.