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Aerodynamic characteristics of corn as determined by energy balance techniques

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Aerodynamic resistance to heat transfer (rah) needed to calculate sensible heat flux (H) used in energy balance modeling can be estimated from momentum aerodynamic resistance with corrections for atmospheric stability. This study compared rah and H modeled by four commonly used resistance methods with rah and H measured indirectly through energy balance techniques. Three momentum aerodynamic parameters were calculated: roughness length, Zom; zero plane displacement, d; and friction velocity, U*. Corn (Zea mays L.) was grown on east-west rows (0.75 m wide) in 1989 and 1990 at Bushland, TX, in two contiguous 5-ha fields where two weighing lysimeters were located and micrometeorological measurements were made. Sensible heat flux was indirectly measured as a residual of the energy balance and then used to calculate aerodynamic resistance. Momentum aerodynamic parameters were calculated from near-neutral condition wind-speed profiles using a least squares procedure. The momentum parameter relationships to crop height (CH) were d = 0.73 X CH (r2 = 0.59) and Zom = 0.12 X CH r2 = 0.96). While no rah model performed well, the best linear fit (r2 = 0.75, y = 1.08x + 4.2) between measured (x) and modeled (y) rah occurred under stable atmospheric conditions; for measured and modeled H, the best linear fit (r2 = 0.84, y = 0.93x + 62.1) occurred under all atmospheric conditions. Measured rah in neutral and unstable conditions was not closely associated with wind speed. Performance of a model with a limited stability factor was improved by increasing the magnitude of the factor. These results suggest that rah models may be sensitive to atmospheric stability and local conditions such as fetch and leaf area.
Tolk, J.A. , Howell, T.A. , Steiner, J.L. , Krieg, D.R.
Includes references
Agronomy journal May/June 1995. v. 87 (3)
Journal Articles, USDA Authors, Peer-Reviewed
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