| Abstract: | Determination of fetch requirements for accurate Bowen-ratio measurements of latent- and sensible-heat fluxes is more involved than for eddy-correlation measurements because Bowen-ratio sensors are located at two heights, rather than just one. A simple solution to the diffusion equation is used to derive an expression for Bowen-ratio fetch requirements, downwind of a step change in surface fluxes. These requirements are then compared to eddy-correlation fetch requirements based on the same diffusion equation solution. When the eddy-correlation and upper Bowen-ratio sensor heights are equal, and the available energy upwind and downwind of the step change is constant, the Bowen-ratio method requires less fetch than does eddy correlation. Differences in fetch requirements between the two methods are greatest over relatively smooth surfaces. Bowen-ratio fetch can be reduced significantly by lowering the lower sensor, as well as the upper sensor. The Bowen-ratio fetch model was tested using data from a field experiment where multiple Bowen-ratio systems were deployed simultaneously at various fetches and heights above a field of bermudagrass. Initial comparisons were poor, but improved greatly when the model was modified (and operated numerically) to account for the large roughness of the upwind cotton field. |
| Genre: | Article |
| ProdID: | 70019253 |
| Citation Author: | Stannard, D. I. |
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| Citation End Page: | 406 |
| Citation Issue: | 3 |
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| Citation Language: | English |
| Citation Larger Work Title: | Boundary-Layer Meteorology |
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| Citation Number Of Pages: | 32 |
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| Citation Search Results Text: | A theoretically based determination of bowen-ratio fetch requirements; 1997; Article; Journal; Boundary-Layer Meteorology; Stannard, D. I. |
| Citation Start Page: | 375 |
| Citation Volume: | 83 |
| Citation Year: | 1997 |
| Type: | citation/reference |
| Text: | A theoretically based determination of bowen-ratio fetch requirements; 1997; Article; Journal; Boundary-Layer Meteorology; Stannard, D. I. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| Date Other: | Wed, 1 Jan 1997 00:00 -0600 |
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