The effect of canopy-snow on the energy balance above a coniferous forest

✍ Scribed by Yuichiro Nakai; Tomoki Sakamoto; Tomomi Terajima; Kenzo Kitamura; Tomoki Shirai

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 445 KB
• Volume: 13
• Category: Article
• ISSN: 0885-6087
• DOI: 10.1002/(sici)1099-1085(199910)13:14/15<2371::aid-hyp871>3.0.co;2-1

✦ Synopsis

To evaluate an interactive eect 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 ¯uxes above the canopy were measured using the eddy and band-pass covariance method. The diurnal courses of the measurements showed that turbulent ¯uxes were sensitive to the snow on the canopy. Latent heat ¯uxes dominated above the snow-covered canopy and sensible heat ¯ux prevailed above the snowfree canopy. The eect of the canopy-snow on turbulent energy exchange was examined using the evaporative eciency for the canopy-layer in an energy balance model composed of two sources of vapor ¯uxes. The evaporative eciency 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 eciency and the fraction of the canopy-snow area. The snowcover season in the study site can be classi®ed into the following two types of turbulent ¯ux composition:

(1) in mid-winter, when the canopy was snow-covered, latent heat ¯ux dominated and the Bowen ratio was positive and low; (2) during the snowmelt season, sensible heat ¯ux from the dry canopy prevailed and the Bowen ratio was much larger than in mid-winter.