Surface Energy Balance Closure in the Owens Valley, CA

Ideally, the sum of the net radiation and ground heat flux (the available energy) balances the surface turbulent fluxes of sensible and latent heat which drive atmospheric boundary layer processes. However, such a closure in the surface energy balance is rarely achieved, resulting in a residual. This residual is typically on the order of 10-30 % of the total available energy with the sum of the turbulent fluxes smaller than the available energy. It is now well established that this residual cannot be solely attributed to measurement uncertainties. Other reasons for a non-closure in the energy balance include the presence of surface heterogeneities and large scale eddies, the presence of thermally and terrain forced flows, and varying flux footprints.

The objective of this study is to identify and quantify the sources of non-closure in the energy balance using data collected during the Terrain-Induced Rotor Experiment in Owens Valley, CA in spring 2006 In particular we use turbulent and latent heat flux data collected at three 34-m towers distributed along the valley's central axis and its western sidewall. We determine the residual in the energy balance as a function of the measurement level of the turbulent fluxes, averaging time, the location in the valley, friction velocity, stability, non-stationarity, and the presence of valley and slope flows. We demonstrate that knowledge of the dependency of the residual on these factors is crucial for a proper evaluation of surface layer parameterizations in complex mountainous terrain.