View source for Mountain-valley wind systems



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== mountain&ndash;valley wind systems ==
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<div class="definition"><div class="short_definition">The [[diurnal]] cycle of [[local winds]] in a mountain valley during  [[clear]] or mostly clear periods of weak [[synoptic]] flow.</div><br/> <div class="paragraph">The traditional components of the [[cycle]] are upslope ([[anabatic]]) winds, the daytime [[upvalley wind|upvalley  wind]], downslope ([[katabatic wind|katabatic]]) winds, and the nighttime [[downvalley wind]] (Defant,1951). In this  traditional view, each component has corresponding compensatory currents aloft, presumably to  form a [[closed circulation]]. For example, the downvalley wind would lie beneath a wind aloft  directed up the valley. Observationally, these compensatory currents have been verified in some  cases but not found in others. The classic [[model]] has the upvalley wind continuing until after  [[sunset]], but in many semiarid regions (or during dry periods), when the [[Bowen ratio]] is large and  the surface [[heat flux]] is strong, boundary layer [[convection]] interrupts this model by [[mixing]] ridgetop  winds down to the surface for much of the mid- to late afternoon. Where the valley opens onto  a plain, a [[valley outflow jet]], which represents a continuation of the downvalley wind, often extends  many kilometers over the plain at night. Variations from this basic scheme arise from valley  orientation, especially affecting the transition periods. In a north&ndash;south valley, for example, sunset  occurs first on the east-facing slopes, and katabatic flows begin earlier there, which can result in  [[cross-valley winds]] connecting with anabatic flow components on the west-facing sidewalls still  in the sun. Similarly, at [[sunrise]] the east-facing slope is exposed to [[sunshine]] earlier than the rest  of the valley, and therefore anabatic flows begin earlier there.</div><br/> </div><div class="reference">Defant, F. 1951. Compendium of Meteorology. 663&ndash;665. </div><br/> <div class="reference">Banta, R. M., and W. R. Cotton 1981. An analysis of local wind systems in a broad mountain basin. J.  Climate Appl. Meteor.. 20. 1255&ndash;1266. </div><br/> <div class="reference">Whiteman. C. D. 1990. Observations of thermally developed wind systems in mountainous terrain. Meteorol.  Monographs. 45. 5&ndash;42. </div><br/> 
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