An assessment of corrections for eddy covariance measured turbulent fluxes over snow in mountain environments

Authors: Reba, Michele; LINK, TIMOTHY - University Of Idaho; Marks, Daniel; POMEROY, JOHN - University Of Saskatchewan

Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/6/2009
Publication Date: 8/18/2009
Citation: Reba, M.L., Link, T.E., Marks, D.G., Pomeroy, J. 2009. An Assessment of Corrections for Eddy Covariance Measured Turbulent Fluxes Over Snow in Mountain Environments. Water Resources Research, 45, W00D38, doi:10.1029/2008WR007045.

Interpretive Summary: Snow makes up a significant portion of the precipitation received annually in the inter-mountain western US. Radiation and the turbulent fluxes of sensible and latent heat are the primary contributors of energy to the snowcover. It is difficult to measure turbulent fluxes while there is a long history of accurately measuring and modeling radiation. Currently, the most reliable method available to measure sensible and latent heat flux is eddy covariance. Eddy covariance measurements were made at two sites for three consecutive snow seasons. Analysis of the data quality and post-processing procedure are explored to verify the validity of the measurements made. Ultimately the measurements will be used to validate modeled values of sensible and latent heat flux. These models will further our ability to use physically based models to simulate the hydrology of snow dominated catchments.

Technical Abstract: Snow-covered complex terrain is an extremely important runoff generating landscape in high altitude and latitude environments, yet is often considered non-viable for eddy covariance measurements of turbulent fluxes. Turbulent flux data are useful for evaluating the coupled snow cover mass and energy balance that control snow ablation and melt. In particular, detailed, multi-season analyses of eddy covariance data post-processing requirements and resulting data quality for hydrological analyses in open and sheltered mountain sites have not been conducted. These analyses are needed, since these landscapes typify those that generate snowmelt runoff in the mountain west of North America. Eddy covariance measurements taken from exposed hilltop and sheltered sub-canopy snow research sites during three snow seasons underwent rigorous post-processing and data quality assessments. Procedures included data filtering, air density corrections, sensor heating, axis rotation, and exclusion of instationary data. Data quality analysis showed that 77% of the sensible heat flux data and 95% of the latent heat flux data were of high quality. There was little inter-annual variability over three seasons in quality or improvements due to post-processing results. A comparison of summary data based on a 30-minute averaging period to post-processed high-resolution flux data found that the post-processed sensible heat fluxes were up to 14% less than the summary fluxes for the snow season. The results indicated that application of unattended eddy covariance techniques at these sites was viable, but that the full suite of corrections and post-processing are advised to obtain flux observations of sufficient reliability for snow hydrology calculations.