Energy balance closure over a cool temperate forest in steeply sloping topography during snowfall and snow-free periods

Abstract

This study evaluated energy balance closure in the eddy covariance method in a cool-temperate evergreen coniferous forest on steeply sloping topography in a region that experiences snowfall. We investigated the ratio of the sum of sensible and latent heat fluxes to available energy (the energy balance ratio; EBR) and the slope of the regression line of the eddy fluxes against available energy (closure ratio; CR). The 3 yr of continuous data were divided into snowfall (November-April) and snow-free periods (May-October). Uncorrected EBR and CR values at this site were 0.56 and 0.44 during the snowfall period and 0.69 and 0.60 during the snow-free period, respectively. Corrections of the storage term, the AOA error, and the inclined surface improved EBR by 2.0-2.6%, 8.3-8.9% and 4.9-5.9%, and improved CR by 5.3-5.8%, 5.6-7.9%, and 4.0-5.4%. Consequently, EBR and CR reached 0.86 and 0.79 during the snow-free period. By also considering the heat of fusion, EBR reached 0.79 during the snowfall period. Our findings suggest that heat fluxes of eddy-covariance measurements over a forest on steep slopes have a similar accuracy as those over other topography.