11.8
Comparison of Methods to Infer Gas Fluxes off a Lagoon
John D. Wilson, University of Alberta, Edmonton, AB, Canada; and T. K. Flesch and L. A. Harper
Field techniques in agro-meteorology are always predicated on assumptions (eg. spatial symmetry, and/or the "similarity" of transport efficiencies of different species). When these methods spread to related fields of study, there is a danger that users may pick up the technical procedures (instruments and algorithms), but lose sight of the crucial assumptions.
We performed a "synthetic experiment" to determine the accuracy with which gas fluxes (Q, kg m-2 s-1) off a small lagoon may be estimated from measured gas concentrations C (or concentration differences DC) over water, using a local advection model to generate the fields of windspeed, temperature and gas concentration. From these "data" we deduced several micro-meteorological estimators of the (known) source strength Q. Estimates by integration of the horizontal flux (QIHF) are the most satisfactory, followed by estimates using a source-receptor relationship based on a backward Lagrangian stochastic method (QbLS). Flux-gradient estimates QFG, which posit horizontally-uniform wind and stability, can be very seriously in error, and should not be used in advective flows.
Session 11, Contributions to Experimental and Theoretical Studies in Agricultural and Forest Meteorology
Friday, 18 August 2000, 3:30 PM-5:30 PM
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