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Boundary-Layer Meteorology

, Volume 138, Issue 2, pp 231–262 | Cite as

Atmospheric Stability Effects on Wind Fields and Scalar Mixing Within and Just Above a Subalpine Forest in Sloping Terrain

  • Sean P. Burns
  • Jielun Sun
  • Donald H. Lenschow
  • Steven P. Oncley
  • Britton B. Stephens
  • Chuixiang Yi
  • Dean E. Anderson
  • Jia Hu
  • Russell K. Monson
Open Access
Article

Abstract

Air temperature T a , specific humidity q, CO2 mole fraction χ c , and three-dimensional winds were measured in mountainous terrain from five tall towers within a 1 km region encompassing a wide range of canopy densities. The measurements were sorted by a bulk Richardson number Ri b . For stable conditions, we found vertical scalar differences developed over a “transition” region between 0.05 < Ri b < 0.5. For strongly stable conditions (Ri b > 1), the vertical scalar differences reached a maximum and remained fairly constant with increasing stability. The relationships q and χ c have with Ri b are explained by considering their sources and sinks. For winds, the strong momentum absorption in the upper canopy allows the canopy sublayer to be influenced by pressure gradient forces and terrain effects that lead to complex subcanopy flow patterns. At the dense-canopy sites, soil respiration coupled with wind-sheltering resulted in CO2 near the ground being 5–7 μmol mol−1 larger than aloft, even with strong above-canopy winds (near-neutral conditions). We found Ri b -binning to be a useful tool for evaluating vertical scalar mixing; however, additional information (e.g., pressure gradients, detailed vegetation/topography, etc.) is needed to fully explain the subcanopy wind patterns. Implications of our results for CO2 advection over heterogenous, complex terrain are discussed.

Keywords

Canopy-layer turbulence Carbon in the Mountains Experiment (CME04) Complex terrain Richardson number Scalar mixing Wind fields 

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Copyright information

© Springer Science+Business Media B.V. 2010

Authors and Affiliations

  • Sean P. Burns
    • 1
    • 4
  • Jielun Sun
    • 1
  • Donald H. Lenschow
    • 1
  • Steven P. Oncley
    • 1
  • Britton B. Stephens
    • 1
  • Chuixiang Yi
    • 2
  • Dean E. Anderson
    • 3
  • Jia Hu
    • 4
  • Russell K. Monson
    • 4
  1. 1.National Center for Atmospheric ResearchBoulderUSA
  2. 2.School of Earth and Environmental SciencesQueens CollegeFlushingUSA
  3. 3.U.S. Geological SurveyDenverUSA
  4. 4.Department of Ecology and Evolutionary BiologyUniversity of ColoradoBoulderUSA

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