Rossby number

Summary

The Rossby number $\mathrm{Ro} = U / (f L)$ is the dimensionless number that compares the inertia of a flow with the Coriolis force due to rotation. It is the main parameter of rotating flows, in particular of the atmosphere and the oceans. When it is small, the flow is close to geostrophic balance, in which the pressure gradient balances the Coriolis force.