Dry Surface Frontogenesis Arising from Interior Potential Vorticity Perturbations in a Semigeostrophic Model

Abstract

We examine the role of interior potential vorticity perturbations in surface frontogenesis using the two-dimensional semigeostrophic Eady model. Fronts form rapidly for properly configured small disturbances even at zonal wavenumbers for which no exponentially unstable modes exist. While lack of exponential growth does not preclude frontal development, the strength of the disturbance must exceed an amplitude threshold for frontal formation. In practice, the finite amplitude constraint is not severe requiring meridional winds of a few meters per second. Model integrations illustrate the variety of frontogenesis phenomena that arise from interior potential vorticity perturbations including formation of near surface vertical velocity maxima.