Submitted to: Journal of Hydrometeorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2008
Publication Date: 7/1/2008
Citation: Marks, D.G., Reba, M., Pomeroy, J., Link, T., Winstral, A.H., Flerchinger, G.N., Elder, K. 2008. Comparing simulated and measured sensible and latent heat fluxes over snow under a pine canopy to improve an energy balance snowmelt model. Journal of Hydrometeorology, 9:1506-1522. Interpretive Summary: Turbulent fluxes of heat and water from the snow surface have a significant effect on the snow heat balance, and the timing and magnitude of melt. While models simulate theses fluxes, they are difficult to validate. Eddy covariance (EC) provides a method to measure turbulent fluxes of heat and water from the snow surface. In this paper, we show how well modeled and measured fluxes from the snow match below a forest canopy. In general, the match is good, but some discrepancies were observed. This experiment shows that EC technology can be used effectively over snow, but that some conditions such as storms and very calm periods at night may cause difficulties with this new technology. It also shows that minor modifications in the model configuration can significantly improve the match to measured fluxes.
Technical Abstract: During the second year of the NASA Cold Lands Processes Experiment (CLPX) an eddy covariance (EC) system was operated at the local snow observation site (LSOS) from mid-February to June, 2003. The EC system was located beneath a uniform pine canopy where the trees are regularly spaced and are of similar age and height (Hardy et al., 2004). EC data on sensible and latent heat flux between the snow cover and the atmosphere during the period the system was in operation are presented and compared to those simulated by an energy balance snowmelt model (Snobal). Turbulent fluxes were very important to the snowcover energy balance in the pre-melt and ripening period (March to early May), and so determine the internal energy content of the snowcover as melt accelerates in late spring. Simulated snowcover mass and depth closely matched measured values, and simulated sensible heat fluxes generally matched those measured by the EC system. Though latent heat fluxes showed substantial differences between measurements and model, cumulative sublimation differences were small. Differences between EC-measured and simulated fluxes occurred primarily at night. Specification of a thinner surface layer in the model reduced flux differences between measurement and model. When only daytime fluxes were compared, EC-measured fluxes were very similar to simulated fluxes. This experiment demonstrates the use of eddy covariance methods for measuring heat and mass fluxes from snowcovers at a low-wind, below canopy sites, and shows that EC-measured fluxes can be used to diagnose the performance of snowcover energy balance models in addition to traditional mass balance methods.