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Micrometeorological Techniques

Micrometeorological Techniques. Surface Energy Balance R n - G = H + LE. Historical Perspective. Major advances in 1950s using Osborne Reynolds, (1895) Reynolds averaging eddy covariance Fast response hot –wire anemometer & thermometry

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Micrometeorological Techniques

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  1. Micrometeorological Techniques Surface Energy Balance Rn- G = H + LE

  2. Historical Perspective • Major advances in 1950s using Osborne Reynolds, (1895) Reynolds averaging eddy covariance • Fast response hot –wire anemometer & thermometry • Efforts focused on developing theory, instrumentation & methods • Test scaling concepts of M-O • Spectral/statistical properties of turb. SBL • Osborne Reynolds, 1895, Reynolds averaging – EC • Fickian diffusion led early fluid mech. (Prandtl, Taylor, Bowen) to propose flux-gradient app. (1920’s) • Monin-Obukov 1940s, theoretical principles for computing fluxes in sfc layer • Kolmogorov, statistician, theory for interpreting turb. decay

  3. Lysimeters • Simple in concept • Direct meas. of E • Change of mass • Can be accurate • No assumptions • No gradients • No diffusivities • Relatively small area (0.05-40 m2) • Does it represent surface of interest? • Not versatile • Baseline data

  4. Bowen Ratio LE = Rn– G/1+β • Inexpensive • Simple/practical • Reasonably versatile • Soil water is avail. • No aerodynamic data minimal post processing • Can be reliable • Neutral conditions • Small gradients • kh, ke not equal • Accuracy – Rn and G and true gradients of T and e

  5. Eddy Covariance • Physically based • Direct meas. of E • Versatile, easy, robust • Does not rely on assumptions @ eddy diffusivity • Highly accurate/inaccurate • High frequency data • Expensive • Corrections required • Post processing intensive

  6. Scintillometers • Optical device • Meas. small fluctuations in refractive index of air (T, P e) • Versatile • Robust • Ease of operation • Well suited for heterogeneous • H integrated transect • Expensive • Needs u* • Valid M-O assumptions • E is a residual from SEB

  7. Summary • Theoretical development • Instrumentation to test the theory • Multiple systems/methods - all try for LE • Spatial and temporal issues • Surface variability • Sufficient number of spatially representative sites • Continuity of data flow • Uniformity of meas. and processing QA/QC

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