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Encyclopedia > Ekman number

The Ekman number, named for V. Walfrid Ekman, is a dimensionless number used in describing geophysical phenomena in the oceans and atmosphere. It characterises the ratio of viscous forces in a fluid to the fictitious forces arising from planetary rotation.


It is defined as:

- where D is a characteristic (usually vertical) length scale of a phenomenon; ν, the kinematic eddy viscosity; Ω, the angular velocity of planetary rotation; and φ, the latitude. The term 2 Ω sin φ is the Coriolis frequency.


When the Ekman number is small, disturbances are able to propagate before decaying owing to frictional effects.


  Results from FactBites:
 
Ekman number Biography on DanceAge (271 words)
The Ekman number describes the order of magnitude for the thickness of an Ekman layer, a boundary layer in which viscous diffusion is balanced by Coriolis effects, rather than the usual convective inertia.
NRL states that this latter definition is equivalent to the root of the ratio of Rossby number to Reynolds number.
Ekman • Euler • Froude • Galilei • Grashof • Hagen • Knudsen • Laplace • Lewis • Mach • Marangoni • Nusselt • Ohnesorge • Péclet • Prandtl • Rayleigh • Reynolds • Richardson • Rossby • Schmidt • Sherwood • Stanton • Stokes • Strouhal • Weber • Weissenberg • Womersley
Dimensionless number - Wikipedia, the free encyclopedia (1041 words)
Such a number is typically defined as a product or ratio of quantities which have units of identical dimension, in such a way that the corresponding units can be converted to identical units and then cancel.
An angle measured this way is the length of arc lying on a circle (with center being the vertex of the angle) swept out by the angle to the length of the radius of the circle The units of the ratio is length divided by length which is dimensionless.
The power consumption of a stirrer with a particular geometry is a function of the density and the viscosity of the fluid to be stirred, the size of the stirrer given by its diameter, and the speed of the stirrer.
  More results at FactBites »


 

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