Abstract
Understanding and prediction of the stable atmospheric boundary layer is challenging. Many physical processes come into play in the stable boundary layer, i.e. turbulence, radiation, land surface coupling and heterogeneity, orographic turbulent and gravity wave drag. The development of robust stable boundary-layer parameterizations for weather and climate models is difficult because of the multiplicity of processes and their complex interactions. As a result, these models suffer from biases in key variables, such as the 2-m temperature, boundary-layer depth and wind speed. This short paper briefly summarizes the state-of-the-art of stable boundary layer research, and highlights physical processes that received only limited attention so far, in particular orographically-induced gravity wave drag, longwave radiation divergence, and the land-atmosphere coupling over a snow-covered surface. Finally, a conceptual framework with relevant processes and particularly their interactions is proposed.
Highlights
The atmospheric boundary layer over land experiences a clear diurnal cycle driven by that of the incoming solar radiation
The gravity wave drag (GWD) is highly variable throughout the night, and varies on a timescale that is close to that of the observed global intermittent turbulence. These results suggest that orographically induced GWD is a possible candidate to explain that drag is too small in NWP models
The stable boundary layer (SBL) is governed by a myriad of physical processes
Summary
The atmospheric boundary layer over land experiences a clear diurnal cycle driven by that of the incoming solar radiation. The SBL is governed by a multiplicity of processes such as turbulence, radiative cooling, the interaction with the land surface, gravity waves, katabatic flows, fog and dew formation. In order to obtain accurate forecasts of the synoptic flow, atmospheric models generally require a larger turbulent drag at the surface and in the boundary layer than can be justified from field observations (e.g., Holtslag et al, 2013).
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