title: On the energy balance closure and net radiation in complex terrain.
abstract: In complex, sloping terrain, horizontal measurements of net radiation are not reflective of the radiative energy available for the conductive and convective heat exchange of the underlying surface. Using data from a grassland site on a mountain slope characterised by spatial heterogeneity in inclination and aspect, we tested the hypothesis that a correction of the horizontal net radiation measurements which accounts for the individual footprint contributions of the various surfaces to the measured sensible and latent heat eddy covariance fluxes will yield more realistic slope-parallel net radiation estimates compared to a correction based on the average inclination and aspect of the footprint. Our main result is that both approaches led to clear, but very similar improvements in the phase between available energy and the sum of the latent and sensible heat fluxes. As a consequence the variance in the sum of latent and sensible heat flux explained by available radiation improved by >10 %, while energy balance closure improved only slightly. This is shown to be mainly due to the average inclination and aspect corresponding largely with the inclination and aspect of the main flux source area in combination with a limited sensitivity of the slope correction to small angular differences in, particularly, inclination and aspect. We conclude with a discussion of limitations of the present approach and future research directions.
authors.affiliation: Institute of Ecology, University of Innsbruck, Sternwartestr. 15, 6020 Innsbruck, AUSTRIA; Institute for Alpine Environment, European Academy of Bolzano, Drususalle 1, 39100 Bolzano, ITALY; Institute for Applied Remote Sensing, European Academy of Bolzano, Drususalle 1, 39100 Bolzano, ITALY.
authors.forename: Georg
authors.initials: G
authors.lastname: Wohlfahrt
authors.affiliation: Institute of Ecology, University of Innsbruck, Sternwartestr. 15, 6020 Innsbruck, AUSTRIA.
authors.forename: Albin
authors.initials: A
authors.lastname: Hammerle
authors.affiliation: Institute for Alpine Environment, European Academy of Bolzano, Drususalle 1, 39100 Bolzano, ITALY.
authors.forename: Georg
authors.initials: G
authors.lastname: Niedrist
authors.affiliation: Institute of Ecology, University of Innsbruck, Sternwartestr. 15, 6020 Innsbruck, AUSTRIA.
authors.forename: Katharina
authors.initials: K
authors.lastname: Scholz
authors.affiliation: Institute for Applied Remote Sensing, European Academy of Bolzano, Drususalle 1, 39100 Bolzano, ITALY.
authors.forename: Enrico
authors.initials: E
authors.lastname: Tomelleri
authors.affiliation: Institute of Ecology, University of Innsbruck, Sternwartestr. 15, 6020 Innsbruck, AUSTRIA.
authors.forename: Peng
authors.initials: P
authors.lastname: Zhao
keywords: eddy covariance; footprint; grassland; slope