Turbulent flux measurements above and below the overstory of a boreal aspen forest

被引:151
|
作者
Blanken, PD
Black, TA
Neumann, HH
Den Hartog, G
Yang, PC
Nesic, Z
Staebler, R
Chen, W
Novak, MD
机构
[1] Univ British Columbia, Vancouver, BC V5Z 1M9, Canada
[2] Atmospher Environm Serv, Downsview, ON, Canada
关键词
BOREAS; eddy correlation; eddy covariance; turbulence; understory;
D O I
10.1023/A:1001557022310
中图分类号
P4 [大气科学(气象学)];
学科分类号
0706 ; 070601 ;
摘要
Turbulent flux measurements both above and beneath the canopy of a boreal aspen forest are described. Velocity skewness showed that, beneath the aspen canopy, turbulence was dominated by intermittent, downward penetrating gusts. Eulerian horizontal length scales calculated from integration of the autocorrelation function or spectral peaks were 9.0 and 1.4 times the mean aspen height of 21.5 m respectively. Above-canopy power spectral slopes for all velocity components followed the -2/3 power law, whereas beneath-canopy slopes were closer to -1 and showed a spectral short cut in the horizontal and vertical components. Cospectral patterns were similar both above and beneath the canopy. The Monin-Obukhov similarity function for the vertical wind velocity variance was a well-defined function of atmospheric stability, both above and beneath the canopy. Nocturnal flux underestimation and departures of this similarity function from that expected from Monin-Obukhov theory were a function of friction velocity. Energy balance closure greater than 80% was achieved at friction velocities greater than 0.30 and 0.10 m s(-1), above and below the aspen canopy, respectively. Recalculating the latent heat flux using various averaging periods revealed a minimum of 15 min were required to capture 90% of the 30-min flux. Linear detrending reduced the Bur at shorter averaging periods compared to block averaging. Lack of energy balance closure and erratic flux behaviour led to the recalculation of the latent and sensible heat fluxes using the ratio of net radiation to the sum of the energy balance terms.
引用
收藏
页码:109 / 140
页数:32
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