Rossby number

In rotating flows (e.g. geophysical flows), the Rossby number is defined as the ratio of the advective acceleration to the Coriolis acceleration. Alternately, it may be thought of as the ratio of the inertial force to the Coriolis force.

$Ro = \frac{\left( \frac{U^2}{L} \right) }{ \left( \Omega U \right) } = \frac{U}{\Omega L}$

where $\Omega$ is the angular speed of rotation, U is the velocity scale and L is the lenth scale.