The effect of the continental boundary layer on the dynamics of fronts in a 2D model of baroclinic instability. I: An insulated lower surface

The effect of boundary-layer turbulence on the structure and evolution of the surface front that develops in the finite-amplitude Eady wave is examined. A no-slip condition is imposed at the lower boundary, and the boundary-layer turbulence is parametrized using either the Blackadar scheme, the Mellor-Yarnada 2(1)/(4) scheme or the ECMWF scheme. The study builds on the influential work of Keyser and Anthes. It is shown that the low-level structure of the front, and especially the pre-frontal updraught, is sensitive to the depth of the boundary layer. In particular, the pre-frontal updraught intensifies when the boundary layer deepens because the vertically integrated cross-isobaric mass flux increases. The numerical experiments also show that the frictionally induced convergence strengthens the cross-front potential temperature gradient, and that the convergence itself is determined by the horizontal variation in net pressure gradient force (that part of the pressure gradient force not balanced by the Coriolis force). While surface sensible heat fluxes are neglected here, their effect is explored in a companion paper.