Answer:
In areas characterized by complex terrain and in the absence of strong to moderate synoptic forcing, mountain weather is dominated by local-scale thermal circulation. The main forcing of thermal circulation is solar radiation which determines, with it’s day-night alternation, convective mixing during daytime and stable layering during nighttime. Flows follow this alternation: daytime convection triggers upvalley/ upslope anabatic wind flows that climb up the relief; nighttime stratification features gravity-driven downvalley/downslope katabatic wind flows. Flow reversal is not instantaneous but spaced out by evening transition, which is characterized by slow winds, changing wind directions, and fluxes close to zero. Evening transition at Sagebrush site (Dugway Proving Ground, Utah, US) has been studied by analyzing tethered balloon data collected during MATERHORN Spring 2013 campaign. Good qualitative and quantitative agreement has been found between data results and Stagnation front model proposed by [Hunt, J. C R, Fernando, H. J. S., Princevac, 2003], especially in estimating time delay for flow reversal, i.e. the duration of transition. Slab formation model by [Fernando et al., 2013] has also been tested but with poor agreement. Facts for a cold-air pool formation has been supplied and discussed.
Explanation:
