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| | | #REDIRECT [[Geostrophic wind]] |
| #REDIRECT [[geostrophic wind]] | |
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| == geostrophic wind ==
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| <div class="definition"><div class="short_definition">That horizontal [[wind]] velocity for which the [[Coriolis acceleration]] exactly balances the [[horizontal pressure force]]: <div class="display-formula"><blockquote>[[File:ams2001glos-Ge29.gif|link=|center|ams2001glos-Ge29]]</blockquote></div> where '''v'''<sub>''g''</sub> is the geostrophic wind, ''f'' the [[Coriolis parameter]], '''k''' the vertical unit [[vector]], ''g'' the [[acceleration of gravity]], '''∇'''<sub>''p''</sub> the horizontal [[del operator]] with [[pressure]] as the vertical coordinate, and ''z'' the height of the [[constant-pressure surface]].</div><br/> <div class="paragraph">The geostrophic wind is thus directed along the [[contour]] lines on a constant-pressure surface (or along the isobars in a [[geopotential surface]]) with low elevations (or low pressure) to the left in the Northern Hemisphere and to the right in the Southern Hemisphere. The speed of the geostrophic wind ''V''<sub>''g''</sub> is given by <div class="display-formula"><blockquote>[[File:ams2001glos-Ge30.gif|link=|center|ams2001glos-Ge30]]</blockquote></div> where ∂''z''/∂''n'' is the slope of the [[isobaric surface]] normal to the contour lines to the left of the direction of motion in the Northern Hemisphere and to the right in the Southern Hemisphere. The geostrophic wind is defined at every point except along the [[equator]]. The validity of this approximation in dynamic theory depends upon the particular context. <br/>''See'' [[geostrophic equilibrium]], [[geostrophic approximation]], [[quasigeostrophic approximation]]; <br/>''compare'' [[gradient wind]].</div><br/> </div>
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