A THEORETICAL-STUDY OF COLD-AIR DAMMING WITH UPSTREAM COLD-AIR INFLOW

The previously developed two-layer model of cold air damming is extend ed to include upstream cold air inflow. The upper layer is an isentrop ic cross-mountain flow. The lower layer is a cold boundary layer Bow p artially blocked by a two-dimensional mountain with a cold dome formed on the windward side of the mountain. The interface represents a slop ing inversion layer coupling the two layers. The shape of the interfac e can be approximated by a cubic polynomial, and the interfacial coupl ing condition yields a set of algebraic equations that quantify the sc ale and intensity of the dammed flow as functions of the external para meters characterizing the environmental conditions. It is found that t he cold dome shrinks as the Froude number increases or, to a minor deg ree, as the Ekman number decreases or/and the upstream inflow veers fr om northeasterly to south-easterly (with respect to a longitudinal mou ntain to the west). The mountain-parallel jet speed increases as the E kman number decreases or/and the upstream inflow veers from southeaste rly to northeasterly or, to a minor degree, as the Froude number decre ases. The theoretical results are qualitatively verified by numerical simulations with a full model and interpreted physically in comparison with the results of the previous two-layer model. It is also shown th at our two-dimensional model may (or may not) be applied to a quasi-tw o-dimensional mountain ridge if the length scale of the ridge is (or i s not) significantly larger than the Rossby radius of deformation mult iplied by the inverse Froude number.