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Title: Turbulent exchange of momentum and carbon dioxide of a Sitka spruce plantation
Author: McCracken, Peter J.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1993
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Our knowledge of the global carbon budget is at present insufficient to predict reliably the possible consequences of rising CO2 levels on the climate and on ecosystems. Attempts to close the global carbon budget have indicated that a major sink for CO2 may exist in the boreal forests of the northern hemisphere, (Tans et al., 1990). This thesis reports on field experiments which were undertaken to investigate the turbulent exchange of mass, energy and momentum in a northern hemisphere coniferous forest, with special attention to the exchange of carbon dioxide. The eddy covariance technique was used to measure mass, energy and momentum fluxes above and within a Sitka spruce, (Picea sitchensis (Bong.) Carr.), plantation in South West Scotland. The forest had a mean height, h, of 15 m, was densely planted and unthinned. Measurements were made at heights of 1.2h, 0.7h and 0.1h, where the heights within the canopy corresponded to the lower canopy crown and the dead branch trunkspace, respectively. The upper canopy was found to be efficient at attenuating momentum, with momentum fluxes at 0.7h being only 2 - 3% of those at 1.2h. Spectral slopes of velocity and scalar quantities were considerably steeper than expected from Similarity theory indicating a more rapid dissipation of larger scale motions than above the canopy. Evidence was found to support the existence of large, intermittent and energetic structures dominating the turbulent exchange in the forest. Eularian integral time scales for streamwise (Lu) and vertical (Lw) velocities were calculated at 1.2h as ~ h and ~ 0.2h, respectively. A momentum quadrant analysis indicated that ~ 50% of momentum flux, 21 - 47% of CO_2 flux and 23 - 44% of sensible heat flux at 1.2h was accounted for by events with instantaneous momentum fluxes greater than four times the mean value, which occurred only 5 - 12% of the time.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available