Surface Flux Measurements Above a Mountainous Cryptomeria Forest
Date Issued
2010
Date
2010
Author(s)
Cheng, Shih-Min
Abstract
Under ideal or near-ideal conditions, the eddy-covariance (EC) method is a widely used technique in the measurement of sensible heat, water vapor, and CO2 fluxes. Nowadays, adapting the EC method to complex terrain measurements is a challenging topic. It is necessary to examine whether measurements from single eddy covariance system can represent the flow properties of turbulence at complex terrain. The experimental site in this study is located in a valley covered with 57-year-old Cryptomeria plantation at Sitou, Taiwan. The weather is warm and humid through the whole year. The elevation of this area is from 800 to 2000 m above sea level, and the averaged slope is 13.6 degree. The results showed that almost all the coefficient of spatial variation (CV) values for surface fluxes in this study are less than 15%. Moreover, the values of CV in the daytime are smaller than those in the nighttime. This indicates that the flow variables are more homogeneous during daytime. It is noted that the spatial variability of water vapor flux is larger than those for sensible heat and CO2 fluxes; this may due to the complex sources/sinks distribution of water vapor in this site. Under unstable condition, vertical and horizontal wind velocities meet the Monin-Obukhov similarity theory (MOST) predictions, though the similarity constants at different locations are not the same. For scalar variances, temperature follows MOST well, CO2 meets it fairly, but water vapor does not follow the MOST predictions for all the three locations.
Subjects
Surface fluxes
Spatial variance
Coefficient of variance
Similarity theory
Complex terrain
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