The bulk Richardson number (RiBh; defined over the entire stable boundary layer) is commonly utilized in observational and modelling studies for the estimation of the boundary-layer height. Traditionally, RiBh is assumed to be a quasi-universal constant. Recently, based on large-eddy simulation and wind-tunnel data, a stability dependent relationship has been proposed for RiBh. In this study, we analyze extensive observational data from several field campaigns and provide further support for this newly proposed relationship.