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  • 1
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    Feasibility of Measuring Mean Vertical Motion for Estimating Advection (2005)
    In:  CASI
    Details
    Publication Date: 2019-07-11
    Description: Numerous recent studies calculate horizontal and vertical advection terms for budget studies of net ecosystem exchange of carbon. One potential uncertainty in such studies is the estimate of mean vertical motion. This work addresses the reliability of vertical advection estimates by contrasting the vertical motion obtained from the standard practise of measuring the vertical velocity and applying a tilt correction, to the vertical motion calculated from measurements of the horizontal divergence of the flow using a network of towers. Results are compared for three different tilt correction methods. Estimates of mean vertical motion are sensitive to the choice of tilt correction method. The short-term mean (10 to 60 minutes) vertical motion based on the horizontal divergence is more realistic compared to the estimates derived from the standard practise. The divergence shows long-term mean (days to months) sinking motion at the site, apparently due to the surface roughness change. Because all the tilt correction methods rely on the assumption that the long-term mean vertical motion is zero for a given wind direction, they fail to reproduce the vertical motion based on the divergence.
    Keywords: Meteorology and Climatology
    Type: Regional Carbon Dioxide and Water Vapor Exchange Over Heterogeneous Terrain; 109-141; NS1260
    Format: application/pdf
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  • 2
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    Effect of Stability on Mixing in Open Canopies (2005)
    In:  CASI
    Details
    Publication Date: 2019-07-11
    Description: In open canopies, the within-canopy flux from the ground surface and understory can account for a significant fraction of the total flux above the canopy. This study incorporates the important influence of within-canopy stability on turbulent mixing and subcanopy fluxes into a first-order closure scheme. Toward this goal, we analyze within-canopy eddy-correlation data from the old aspen site in the Boreal Ecosystem - Atmosphere Study (BOREAS) and a mature ponderosa pine site in Central Oregon, USA. A formulation of within-canopy transport is framed in terms of a stability- dependent mixing length, which approaches Monin-Obukhov similarity theory above the canopy roughness sublayer. The new simple formulation is an improvement upon the usual neglect of the influence of within-canopy stability in simple models. However, frequent well-defined cold air drainage within the pine subcanopy inversion reduces the utility of simple models for nocturnal transport. Other shortcomings of the formulation are discussed.
    Keywords: Meteorology and Climatology
    Type: Regional Carbon Dioxide and Water Vapor Exchange Over Heterogeneous Terrain; 47-74; NS1260
    Format: application/pdf
    Location Call Number Expected Availability
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