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    Turbulence Spectra and Eddy Diffusivity over Forests

    Source: Journal of Applied Meteorology:;1996:;volume( 035 ):;issue: 008::page 1307
    Author:
    Lee, Xuhui
    DOI: 10.1175/1520-0450(1996)035<1307:TSAEDO>2.0.CO;2
    Publisher: American Meteorological Society
    Abstract: The main objectives of this observational study are to examine the stability dependence of velocity and air temperature spectra and to employ the spectral quantities to establish relations for eddy diffusivity over forests. The datasets chosen for the analysis were collected above the Browns River forest and the Camp Borden forest over a wide range of stability conditions. Under neutral and unstable conditions the nondimensional dissipation rate of turbulent kinetic energy (TKE) over the forests is lower than that from its Monin-Obukhov similarity (MOS) function for the smooth-wall surface layer. The agreement is somewhat better under stable conditions but a large scatter is evident. When the frequency is made nondimensional by the height of the stand (h) and the longitudinal velocity at this height (uh, the Kaimal spectral model for neutral air describes the observations very well. The eddy diffusivity formulation K = c σ4w/? provides a promising alternative to the MOS approach, where σw is the standard deviation of the vertical velocity and ? TKE dissipation rate. Current datasets yield a constant of 0.43 for c for sensible heat in neutral and stable air, a value very close to that for the smooth-wall surface layer. It is postulated that c is a conservative parameter for sensible heat in the unstable air, its value probably falling between 0.41 and 0.54. In the absence of ? data, it is possible to estimate K from measurements of the local mean wind u and air stability. As a special case, it is shown that K = 0.27(uh/uh)σw under neutral stability. This relation is then used to establish a profile model for wind speed and scalar concentration in the roughness sublayer. The analysis points out that uh and h are important scaling parameters in attempts to formulate quantitative relations for turbulence over tall vegetation.
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      Turbulence Spectra and Eddy Diffusivity over Forests

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    http://yetl.yabesh.ir/yetl1/handle/yetl/4147691
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    contributor authorLee, Xuhui
    date accessioned2017-06-09T14:05:54Z
    date available2017-06-09T14:05:54Z
    date copyright1996/08/01
    date issued1996
    identifier issn0894-8763
    identifier otherams-12360.pdf
    identifier urihttp://onlinelibrary.yabesh.ir/handle/yetl/4147691
    description abstractThe main objectives of this observational study are to examine the stability dependence of velocity and air temperature spectra and to employ the spectral quantities to establish relations for eddy diffusivity over forests. The datasets chosen for the analysis were collected above the Browns River forest and the Camp Borden forest over a wide range of stability conditions. Under neutral and unstable conditions the nondimensional dissipation rate of turbulent kinetic energy (TKE) over the forests is lower than that from its Monin-Obukhov similarity (MOS) function for the smooth-wall surface layer. The agreement is somewhat better under stable conditions but a large scatter is evident. When the frequency is made nondimensional by the height of the stand (h) and the longitudinal velocity at this height (uh, the Kaimal spectral model for neutral air describes the observations very well. The eddy diffusivity formulation K = c σ4w/? provides a promising alternative to the MOS approach, where σw is the standard deviation of the vertical velocity and ? TKE dissipation rate. Current datasets yield a constant of 0.43 for c for sensible heat in neutral and stable air, a value very close to that for the smooth-wall surface layer. It is postulated that c is a conservative parameter for sensible heat in the unstable air, its value probably falling between 0.41 and 0.54. In the absence of ? data, it is possible to estimate K from measurements of the local mean wind u and air stability. As a special case, it is shown that K = 0.27(uh/uh)σw under neutral stability. This relation is then used to establish a profile model for wind speed and scalar concentration in the roughness sublayer. The analysis points out that uh and h are important scaling parameters in attempts to formulate quantitative relations for turbulence over tall vegetation.
    publisherAmerican Meteorological Society
    titleTurbulence Spectra and Eddy Diffusivity over Forests
    typeJournal Paper
    journal volume35
    journal issue8
    journal titleJournal of Applied Meteorology
    identifier doi10.1175/1520-0450(1996)035<1307:TSAEDO>2.0.CO;2
    journal fristpage1307
    journal lastpage1318
    treeJournal of Applied Meteorology:;1996:;volume( 035 ):;issue: 008
    contenttypeFulltext
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    DSpace software copyright © 2002-2015  DuraSpace
    نرم افزار کتابخانه دیجیتال "دی اسپیس" فارسی شده توسط یابش برای کتابخانه های ایرانی | تماس با یابش
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