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ARS Home » Pacific West Area » Boise, Idaho » Northwest Watershed Research Center » Research » Publications at this Location » Publication #225635

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

item Marks, Daniel

Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/6/2009
Publication Date: N/A
Citation: N/A

Interpretive Summary: Eddy Covariance (EC) is a technique that is used to measure the exchange of heat and water vapor between the surface and the atmosphere. In this paper, we test the EC methodology at two sites in the Reynolds Creek Experimental Watershed (NWRC) over snow for three years. One of the sites is on a ridge exposed to the wind, while the other is a sheltered location in an Aspen grove. Different methods for processing and correcting the data are evaluated, to determine the viability of the EC methodology over snow in mountainous terrain. This research shows that EC can be used in complex mountainour terrain over snow at both wind-sheltered and exposed sites to estimate the exchange of water and heat between the atmosphere and the snowcover, but that the EC data must be carefully processed and corrected.

Technical Abstract: Snow is a major component of the annual water balance in many locations across the globe, including the mountainous regions of the interior western U.S. and Canada. Turbulent flux data are useful for evaluating the coupled snow cover mass and energy balance, but such data are rare over snow in complex terrain. The most direct method to measure turbulent fluxes is through the use of eddy covariance (EC), however EC technology has not been widely applied over snow in mountainous regions. This research focuses on the viability of EC technology over snow in mountainous terrain. This is accomplished by filtering data by quality standards based on turbulence theory, and evaluating the difference between the fluxes estimated using several atmospheric corrections (density, axis rotation) to thses covariances. Filtering and correction of EC observations collected at two sites, wind-exposed and sheltered sub-canopy, during the 2004, 2005 and 2006 snow seasons, indicated that EC-measured data and generated fluxes od sensible heat and latent heat from the snow surface was reasonable, and that application of EC-technology at thses sites was viable. Less than 3.4 percent of the data were filtered out for violation of the statistical tests. Air density corrections reduced the seasonal latent flux by one percent to 6.2 percent. Double rotation was found to 75 percent and 93 percent of the data were of sufficient quality for estimation of fluxes for snow hydrologic research. Data quality values were similar to those found by investigators at level sites. A comparision of 30-minute average covariance fluxes to fluxes corrected based on reanalysis of the raw data found that the corrected sensible heat flux was 17 percent to 27 percent less than the uncorrected flux, while the corrected water vapor flux was from three percent more to 11 percent less than the uncorrected flux. This suggests that eddy covariance can be used to estimate fluxes in complex mountain terrain over snow at both exposed and sheltered sub-canopy sites, and in this case, filtering of fluxes based on five minute averages and correcting for atmospheric density and axis rotation were important for flux measurement accuracy.