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:
- <math>Ek=\frac{\nu}{2D^2\Omega\sin\varphi}<math>
- 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 acceleration.
When the Ekman number is small, disturbances are able to propagate before decaying owing to frictional effects.
