Observations of Radiative Flux Divergence under Clear Sky and Fog Conditions

The contribution of radiative heating and cooling to the diurnal change of temperatures in the lowest ten meters of the atmosphere was investigated during the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) Program. Carefully calibrated up- and downfacing pyrgeometers were mounted at two heights above the surface (approximately 2 and 8 m) on meteorological towers and nearby sawhorse-shape structures. Two sites, one on the floor of the Salt Lake Valley, the other on the floor of a smaller, high-elevation valley in Heber, Utah, were instrumented. Radiative heating (radiative flux convergence) and cooling rates (radiative flux divergence) are calculated from the differences in the incoming, outgoing and net longwave fluxes. Initial results from the 2014-2015 winter campaign will be reported, and the magnitude of radiative heating and cooling will be related to sky condition, ground cover (grass or snow) and the formation and development of fog.