Description

The Richardson number is used as a rough measure of expected air turbulence. A lower value indicates a higher degree of turbulence. Values in the range 10 to 0.1 are typical, with values below unity indicating significant turbulence.

Definition

The Richardson number, Ri, is the dimensionless ratio of buoyant suppression of turbulence to shear generation of turbulence and is defined as:

where g is the acceleration of gravity, β a representative vertical convective stability (commonly ∂θ/∂z, where θ is potential temperature), and ∂u/∂z (the change of wind speed with height) is a characteristic vertical shear of the wind. It is used as a dynamic stability measure to determine if turbulence will exist. The Richardson number is a component of the Graphical Turbulence Guidance product available on the U.S. National Oceanic and Atmospheric Administration (NOAA) Aviation Weather Center website.