Radiative scaling of the nocturnal boundary layer

A radiative scaling for the nocturnal boundary layer (NBL) is proposed, based on the mean net longwave for the night-time period when the sensible heat flux is downward. This is a different conceptual framework from models for the NBL based on similarity analysis using stable BL stability functions. A radiative temperature scale, computed from the net outgoing longwave and the slope of the Stefan-Bolzmann law, primarily determines the strength of the NBL and the amplitude of the diurnal temperature range, although the length of the night-time period and the surface wind-speed play subsidiary roles. A related radiative velocity scale, and the length of the night-time period primarily determines the depth of the NBL, although again wind-speed plays an important role. From an observational perspective, this suggests that the diurnal temperature range is a useful measure of net longwave. From a modeling perspective, this provides a framework for evaluating the impact of model physical parameterizations, including the coupling between the surface, the ground and the atmosphere to an observable, the diurnal temperature range. This simple conceptual model is applied to quantify the nocturnal rise of gases such as CO2 and radon that are emitted at the surface.