Aerodynamic conductances at the soil surface in a vineyard
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Knowledge of aerodynamic conductances at the soil surface helps in estimating energy and water vapor fluxes. This research was conducted to determine the effects of wind direction and wind speed on aerodynamic conductances at the soil surface in a vineyard. Aerodynamic conductances for heat transport gh were determined from energy balances on pairs of adjacent sensors, heated and unheated. Twelve-minute average gh values, above-canopy wind speeds u, and wind directions, were measured over a 9 day period in a 5 ha commercial vineyard near Lamesa, TX. In the vineyard, grapevines were growing on vertical, bilateral cordon trellises with cordon wires 1.0 m above the soil surface, and catch wires 0.25 and 0.5 m above the cordon wires. Row and plant spacing were 3.15m and 1.7m, respectively. Sensors were placed beneath the row and at 0.63 m intervals between the rows. Measurements at each location were replicated twice. Spatial mean values of aerodynamic conductances 〈 gh 〉 were calculated as the arithmetic average gh of all locations. For a uniform surface, neither 〈 gh 〉/u1/2 nor gh/〈 gh 〉 should vary with wind direction. Measured values of 〈 gh 〉/u1/2 in the vineyard were 17% higher when the wind direction was parallel to row direction compared with when the wind direction was perpendicular. The spatial distribution of gh/〈 gh 〉 varied with wind direction. The dependence of relative aerodynamic conductances on wind direction for any given wind speed was calculated from the directional dependences of gh/〈 gh 〉 and the ratio of 〈 gh 〉/u1/2 to its directional mean. The relative aerodynamic conductances beneath the row were above unity at wind directions less than 45° from parallel and were only slightly below unity for wind directions perpendicular to the row. The relative conductances near the midpoint between rows were greater than the conductances beneath the row when the wind direction was parallel to the row direction and less than them when the wind direction was perpendicular to the row direction. © 1996 Elsevier Science B.V. All rights reserved.
author list (cited authors)
McInnes, K. J., Heilman, J. L., & Lascano, R. J.