Frontal Interaction with Isolated Orography

Abstract

Abstract The interaction of a three-dimensional cold front and an isolated orographic ridge is examined by means of primitive equation model simulations. The front evolves as part of a developing nonlinear baroclinic wave and propagates southward toward the ridge. Many of the features in this interaction, such as the anticyclonic distortion of the front, divergence and frontolysis on the windward slope, convergence and frontogenesis in the lee, and the frontogenetical forcing associated with tilting, have previously been captured by simulations of a passive scalar traversing a ridge. It is shown that the ridge decelerates the cold postfrontal air and creates a high pressure anomaly on the windward slope. If this anomaly is strong enough, it accelerates air over the ridge peak in a shallow ageostrophic flow that possesses many features found in a gravity current. This current provides relatively strong surface frontogenesis through the convergence term, but cannot transport enough mass across the peak to w...