TY - JOUR
T1 - Atmospheric stability effects on wind fields and scalar mixing within and just above a subalpine forest in sloping terrain
AU - Burns, Sean P.
AU - Sun, Jielun
AU - Lenschow, Donald H.
AU - Oncley, Steven P.
AU - Stephens, Britton B.
AU - Yi, Chuixiang
AU - Anderson, Dean E.
AU - Hu, Jia
AU - Monson, Russell K.
N1 - Funding Information:
Acknowledgements Tony Delany created TGaMS and oversaw its operation during CME04. Andy Watt helped construct, deploy and maintain the AIRCOA systems. Steve Semmer, Gordon Maclean, Kurt Knudsen, Chris Golubieski, and many others at NCAR/ISFF deployed, instrumented, and dismantled the EOL Towers. We thank Dave Bowling for constructive comments on an early version of the manuscript. We also thank two anonymous reviewers for their insightful comments. The NWT tower is supported by a grant from the South Central Section of the National Institute for Global Environmental Change (NIGEC) through the US Department of Energy (BER Program, Cooperative Agreement No. DE-FC03-90ER61010). CME04 was supported by the NCAR Director Opportunity Fund and NSF grant EAR-0321918. The National Center for Atmospheric Research (NCAR) is sponsored by the National Science Foundation.
PY - 2011/2
Y1 - 2011/2
N2 - Air temperature Ta, specific humidity q, CO2 mole fraction χc, 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 Rib. For stable conditions, we found vertical scalar differences developed over a "transition" region between 0.05 < Rib < 0.5. For strongly stable conditions (Rib > 1), the vertical scalar differences reached a maximum and remained fairly constant with increasing stability. The relationships q and χc have with Rib 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 Rib-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.
AB - Air temperature Ta, specific humidity q, CO2 mole fraction χc, 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 Rib. For stable conditions, we found vertical scalar differences developed over a "transition" region between 0.05 < Rib < 0.5. For strongly stable conditions (Rib > 1), the vertical scalar differences reached a maximum and remained fairly constant with increasing stability. The relationships q and χc have with Rib 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 Rib-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.
KW - Canopy-layer turbulence
KW - Carbon in the Mountains Experiment (CME04)
KW - Complex terrain
KW - Richardson number
KW - Scalar mixing
KW - Wind fields
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U2 - 10.1007/s10546-010-9560-6
DO - 10.1007/s10546-010-9560-6
M3 - Article
AN - SCOPUS:78651408056
VL - 138
SP - 231
EP - 262
JO - Boundary-Layer Meteorology
JF - Boundary-Layer Meteorology
SN - 0006-8314
IS - 2
ER -