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Aerodynamic Characteristics of Corn as Determined by Energy Balance Techniques

USDA-ARS, P.O. Drawer 10, Bushland, TX

Jean L. Steiner and Daniel R. Krieg

USDA-ARS, P.O. Box 555, Watkinsville, GA
Dep. of Plant and Soil Science, Texas Tech Univ., Lubbock, TX

^* Corresponding author (Email: !a031cbushlan@attmail.com).

Aerodynamic resistance to heat transfer (r_ah) 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 r_ah and H modeled by four commonly used resistance methods with r_ah and H measured indirectly through energy balance techniques. Three momentum aerodynamic parameters were calculated: roughness length, Z_om; 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 Z_om = 0.12 x CH (r² = 0.96). While no r_ah model performed well, the best linear fit (r₂ = 0.75, y = 1.08x + 4.2) between measured (x) and modeled (y) r_ah 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 r_ah in neutral and unstable conditions was hot 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 r_ah models may be sensitive to atmospheric stability and local conditions such as fetch and leaf area.

Received for publication November 22, 1993.

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