View source for Quasi-hydrostatic approximation



{{TermHeader}}
{{TermSearch}}

<div class="termentry">
  <div class="term">
== quasi-hydrostatic approximation ==
  </div>

<div class="definition"><div class="short_definition">(Or quasi-hydrostatic assumption; <br/>''also called'' hydrostatic approximation.)  The use of the [[hydrostatic equation]] as the vertical [[equation of motion]], thus  implying that the vertical accelerations are small without constraining them to be zero.</div><br/> <div class="paragraph">This compromise takes advantage of the smallness of organized vertical accelerations in [[cyclonic-  scale]] motions while allowing theoretically for a realistic distribution of vertical velocities, which  may be computed from the other equations of a [[closed system]]. Dynamically, the effect of the  quasi-hydrostatic approximation is to eliminate or [[filter]] out the higher frequencies, corresponding  to [[sound waves]] and certain (but not all) [[gravity waves]], from the fundamental equations, while  retaining the frequencies corresponding to cyclonic-scale motions. Combined often with the [[quasigeostrophic  approximation]], this assumption is much used in theoretical work associated with  [[numerical forecasting]]. An example of phenomena to which it is inapplicable is the [[lee wave]].  For the discussion of this and other types of gravity waves, it is common to assume [[hydrostatic  equilibrium]] in the [[basic flow]] but not in the [[perturbation]]. <br/>''See'' [[filtering approximations]].</div><br/> </div>
</div>

{{TermIndex}}
{{TermFooter}}

[[Category:Terms_Q]]