An average measure of turbulence in the stable boundary layer (SBL), defined as the ratio of e-folding depth of cooling to the temperature decrease at the surface. Because the SBL has no well-defined depth, and because the amount of cooling and turbulence intensity varies continuously with height, the bulk scale provides an overall measure of turbulence. Typical magnitudes vary from 3 m K−1 for light turbulence to 15 m K−1 for strong turbulence.