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Harvard Forest Symposium Abstract 2010

  • Title: Quantifying advective and nonstationary effects on eddy fluxes
  • Primary Author: David Fitzjarrald (SUNY at Albany)
  • Additional Authors: Julian Hadley (Harvard Forest); J. William Munger (Harvard University); Ricardo Sakai (SUNY at Albany)
  • Abstract:

    David Fitzjarrald, Ricardo Sakai, Julian Hadley, William Munger.

    We report on ongoing studies of flows within and above the canopy at Harvard Forest, efforts aiming to assess the degree to which horizontal subcanopy motions transport significant amounts of CO2 and to observe perturbations in subcanopy flows induced by the flow aloft. [Recently, several authors argued that Bernoulli effects associated with flow over hills strongly affect subcanopy motions, possibly altering horizontal CO2 advection there [Belcher and Reading, 2008; Finnigan and Belcher, 2004; Katul et al., 2006; Poggi and Katul, 2007; Ross, 2008]. Their arguments are based on scale analyses, wind tunnel experiments, and large eddy simulations. Few, if any, field studies have confirmed the hypothesis.]

    In our earlier work at Harvard Forest [Staebler and Fitzjarrald, 2004], we saw little evidence for such effects. To examine this feature more closely, we set out during the 2009 field observation campaign to complement our ongoing work with sensors designed to obtain observations to document the flow over topography at Harvard Forest. We have continued to operate the subcanopy array at the Little Prospect Hill (LPH) tract. This season, we installed two sodars (acoustic radars; details below). We present preliminary work on characterizing above-canopy flows by direction and intensity, comparing the flow upwind and downwind of the major topographic features, and then attempt to determine the extent to which subcanopy flows are altered. The final step is to document if any effects are sufficient to modify the role of horizontal advection on the subcanopy CO2 budget.

    We form composites of subcanopy motion stratified by wind speed and direction just above the canopy. For a selected period in 2002, we operated two sodars, one well upwind of Prospect Hill and one adjacent to the EMS tower. In 2009 we again established the two sodar sites, this

    time with one near the soil warming experiment. This second sodar was

    destroyed by vandals during the the summer. This crime was attributed by HF personnel successively as the work of bears, smoking bears, or local thugs,though eco-terrorism cannot be ruled out.

  • Research Category: Forest-Atmosphere Exchange

  • Figures:
  • compar.sodar2009.func2.137.149.png