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The effect of canopy‐snow on the energy balance above a coniferous forest
Author(s) -
Nakai Yuichiro,
Sakamoto Tomoki,
Terajima Tomomi,
Kitamura Kenzo,
Shirai Tomoki
Publication year - 1999
Publication title -
hydrological processes
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.222
H-Index - 161
eISSN - 1099-1085
pISSN - 0885-6087
DOI - 10.1002/(sici)1099-1085(199910)13:14/15<2371::aid-hyp871>3.0.co;2-1
Subject(s) - canopy , snow , environmental science , tree canopy , atmospheric sciences , energy balance , eddy covariance , latent heat , snowmelt , sensible heat , leaf area index , hydrology (agriculture) , meteorology , ecology , geography , ecosystem , geology , geotechnical engineering , biology
To evaluate an interactive effect of snow on energy exchange between the forest and atmosphere, the energy balance above a forest was measured continuously between February and April of 1997 in the Hitsujigaoka Experimental Forest, Sapporo, northern Japan. The forest was a dense, 23‐year‐old, coniferous plantation. The study site had frequent snowfalls and the canopy was frequently covered with snow during the study period. Snow‐cover on the canopy was monitored daily using a photo‐camera mounted above the canopy, and the fraction of the snow‐covered area on the canopy was determined as an index of the canopy‐snow condition. Turbulent energy fluxes above the canopy were measured using the eddy and band‐pass covariance method. The diurnal courses of the measurements showed that turbulent fluxes were sensitive to the snow on the canopy. Latent heat fluxes dominated above the snow‐covered canopy and sensible heat flux prevailed above the snow‐free canopy. The effect of the canopy‐snow on turbulent energy exchange was examined using the evaporative efficiency for the canopy‐layer in an energy balance model composed of two sources of vapor fluxes. The evaporative efficiency changed dynamically according to the canopy‐snow condition in the short terms and could be positively related to the extension of the snow‐covered area on the canopy. A quantitative relationship was empirically determined between the evaporative efficiency and the fraction of the canopy‐snow area. The snowcover season in the study site can be classified into the following two types of turbulent flux composition: (1) in mid‐winter, when the canopy was snow‐covered, latent heat flux dominated and the Bowen ratio was positive and low; (2) during the snowmelt season, sensible heat flux from the dry canopy prevailed and the Bowen ratio was much larger than in mid‐winter. Copyright © 1999 John Wiley & Sons, Ltd.