Dry surface frontogenesis associated with interior potential vorticity anomalies in a semi-geostrophic model

We examine the role of interior potential vorticity perturbations in surface frontogenisis using the two dimensional semigeostrophic Eady model. Front form rapidly for properly configured small disturbances even at zonal wavenumbers for which no exponentially unstable modes exsist. While last 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 integration illustrate the variety of frontogenesis phenomena that arise from interior potential vorcitity perturbations including formation of near surface vertical velocity maxima.