MESOSCALE METEOROLOGY | Density Currents

Abstract

Density currents (also known as ‘gravity currents’) in the atmosphere are air flows that are principally due to differences in density (i.e., temperature) between the neighboring bodies of air. Descending cold dense bodies of air are sometimes termed ‘katabatic flows’ or ‘katabatic winds’ at the ground level and ascending heated air constitutes the ‘anabatic winds.’ Such density differences cause lateral pressure gradients, which produce horizontal motion, with cold air moving over the ground into a warmer air mass. They occur on length scales ranging from several hundred meters to hundreds of kilometers. The Earth's rotation (via the Coriolis force) is normally not important for these flows, unless they extend over distances of 100 km or more. In this article, some examples of these flows are provided, and their basic dynamical properties for flows over horizontal ground that move in one direction and that which move radially outward in two dimensions are described, and then density currents that flow downslopes, taking into account the effects of radiative forcing and environmental stratification, are discussed.