Gap winds as hydraulic flows

• Simple models (not discussed) relating wind speed to synoptic-scale horizontal pressure gradients are appropriate for situations where the pressure gradient is entirely determined by synoptic- (ie. large- ) scale processes

• for stratified flow situations, especially where a cold air layer is surmounted by a much less dense air layer, it is possible that pressure gradients within the flow resulting from variations in BL depth are as important as synoptically imposed gradients

• in this situation, gap flow resembles the flow of water in a channel, and thus a hydraulic analogy is appropriate.

• a hydraulic model is a superset of the simpler models which allows along-channel variations in the depth of the cold lower layer and allows pressure gradients resulting from sloped channels

Variable definitions.