Surface Energy Balance Observations during MATERHORN

Observations of the earth's surface energy balance have long been a focus of atmospheric research. The partitioning of the available energy from the sun varies widely by geographic location, land surface type, exposure, soil properties, and available moisture. The energy balance near the surface ultimately controls boundary layer development and evolution, and spatial energy balance differences lead to the formation of thermally driven circulations, such as sea-, lake- and playa breezes, slope- and valley wind circulations. Most of the time, when all components of the energy balance (net radiation, ground heat flux, turbulent sensible and latent heat fluxes) are measured directly, the energy balance is not closed and a residual term remains.

All components of the surface energy balance were directly measured at three different sites using some of the best available instrumentation during the experimental phase of MATERHORN (Mountain Terrain Modeling and Observation Program) conducted at Dugway Proving Ground, Utah, in Fall 2012 and Spring 2013. One site is located in a large sparsely vegetated arid basin, a second on a playa (dry alkali flats which fills with water seasonally to form shallow lakes). The third site is located on a sparsely vegetated slope of an alluvial fan of Granite Peak.

Besides the measurements of the individual short- and longwave components of the radiation balance and eddy-covariance measurements of the turbulent fluxes, our special focus was directed to the soil heat flux. Pairs of self-calibrating heat flux plates were uses at all sites, and the heat storage term above the flux plates was calculated from soil temperature measurements at three levels along with direct observations of the soil's volumetric heat capacity.

Albedo differences between the sites are the main cause of variations in energy input, but we also show how variations in soil properties lead to large differences in the partitioning of the available energy. Differences in the energy balances among the three sites and their implications for boundary layer evolution will be discussed, along with measurement uncertainties and the residual term.