Analysis and Comments on a March 1998 Wedge Event

Analysis and Comments on a March 1998 Wedge Event

The schematic below shows the wind flow in a cold-air damming event. Northeasterly flow under the inversion feeds colder and relatively drier air southward, while a warm and moist easterly flow produces a sloping inversion, producing light precipitation. Also, as the easterly winds rise up the mountain, the air cools adiabatically. Thus, evaporative and adiabatic cooling play a significant role in sustaining the wedge. The air that flows parallel to the mountain range is refered to as a barrier jet. How does the barrier jet evolve? Any air flow that has a component into the mountain will accumulate and decelerate as it approaches the mountian. A deceleration in the flow will produce a decrease in the Coriolis force. Since the pressure gradient force (PGF) remains the same, there will be an imbalance in the geostrophic flow, causing the flow to turn to the left (see diagram below). There is also a weaker secondary pressure gradient force (PGFm) which will cause the flow to change directions. There is mass accumulation as the air builds up on the slopes of the mountain. This pressure gradient force (PGFm) is normal to the mountain range, and when subtracted from the mountain parallel large-scale pressure gradient force (PGF), will cause the air flow to turn to the left. All these processes create a drainage flow that becomes the barrier jet.

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