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Stably stratified canopy flow in complex terrain
Stockholm University, Faculty of Science, Department of Meteorology . City University of New York, USA.
2015 (English)In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 15, 7457-7470 p.Article in journal (Refereed) Published
Abstract [en]

Stably stratified canopy flow in complex terrain has been considered a difficult condition for measuring net ecosystem–atmosphere exchanges of carbon, water vapor, and energy. A long-standing advection error in eddy-flux measurements is caused by stably stratified canopy flow. Such a condition with strong thermal gradient and less turbulent air is also difficult for modeling. To understand the challenging atmospheric condition for eddy-flux measurements, we use the renormalized group (RNG) k–ϵ  turbulence model to investigate the main characteristics of stably stratified canopy flows in complex terrain. In this two-dimensional simulation, we imposed persistent constant heat flux at ground surface and linearly increasing cooling rate in the upper-canopy layer, vertically varying dissipative force from canopy drag elements, buoyancy forcing induced from thermal stratification and the hill terrain. These strong boundary effects keep nonlinearity in the two-dimensional Navier–Stokes equations high enough to generate turbulent behavior. The fundamental characteristics of nighttime canopy flow over complex terrain measured by the small number of available multi-tower advection experiments can be reproduced by this numerical simulation, such as (1) unstable layer in the canopy and super-stable layers associated with flow decoupling in deep canopy and near the top of canopy; (2) sub-canopy drainage flow and drainage flow near the top of canopy in calm night; (3) upward momentum transfer in canopy, downward heat transfer in upper canopy and upward heat transfer in deep canopy; and (4) large buoyancy suppression and weak shear production in strong stability.

Place, publisher, year, edition, pages
2015. Vol. 15, 7457-7470 p.
National Category
Meteorology and Atmospheric Sciences
Research subject
Meteorology; Atmospheric Sciences
URN: urn:nbn:se:su:diva-119196DOI: 10.5194/acp-15-7457-2015ISI: 000357978300019OAI: diva2:843675
Available from: 2015-07-30 Created: 2015-07-30 Last updated: 2015-08-17Bibliographically approved

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