Observations of diurnal and seasonal variation of heat fluxes and an evaluation of bulk Richardson parameterizations in the East River Watershed, Colorado

Multi-scale heterogeneities arising from terrain-induced and land surface variabilities  present in complex ecosystems require accurate measurements and models of surface-atmospheric exchanges. The spatial and temporal variability of energy and water budgets over complex terrain can influence hydrological and biogeochemical interactions that can strongly influence local and regional biosphere-atmosphere transport. Scaling and accurate model representations of these interactions across complex terrains based on single-point or local measurements present a non-trivial scientific challenge. Observations were made of surface energy balance components at NOAA surface flux and mobile SURFRAD radiation stations separated by 5 kilometers along the East River, Colorado, watershed. We present the gap-filled diurnal and seasonal evolution of surface energy balance components as the study domain transitions from low to high snow cover. The spatial variability of the measured fluxes along the valley axis is discussed with the possible influences of local advection and thermally driven circulations. The measured fluxes are compared with a new bulk Richardson number parameterization for sensible heat fluxes over heterogeneous land surfaces, introduced in Lee et al. 2021, and are here extended for complex topography. Our findings provide credence for implementing such a parameterization for surface fluxes and turbulence statistics into land-surface models for representing surface-atmospheric exchanges, although caution should be used during the early-evening transition when there are significant and persistent countergradient fluxes.