AERODYNAMIC CONDUCTANCES ALONG A BARE RIDGE-FURROW TILLED SOIL SURFACE

Spatial dependence of aerodynamic conductances for heat and mass between the atmosphere and positions along the surface of ridge-furrow tilled soil has been ignored in modeling efforts. Aerodynamic conductances may vary with both wind speed and wind direction. This research was conducted to determine the effect of wind direction on aerodynamic conductances for heat transport g(h) from small sensors placed along a bare ridge-furrow tilled soil surface relative to the spatial mean value [g(h)]. Aerodynamic conductances were determined from an energy balance of a pair of adjacent sensors, heated and unheated, placed flush with the soil surface. Twelve minute average gh values, 1 m wind speeds, and wind directions, were measured over a 4 week period in a ridge-furrow tilled field near College Station, Texas. The average vertical distance from the furrow bottoms to the ridge tops was 0.24 m and the horizontal distance between ridges was 1 m. Sensors were placed flush with ridge tops, ridge-furrow sides, and furrow bottoms. To minimize the influence of free convection on g(h), only measurements that were taken when 1 m wind speeds were greater than 0.5 m s-1 were analyzed. Values of g(h)/[g(h)] at the ridge top were 5-10% higher than those at the furrow bottom when the wind was parallel to ridge orientation. When wind was perpendicular to ridge orientation, aerodynamic conductances from sensors on the windward ridge-furrow side were about 5-15% higher than [g(h)], and those from sensors on the leeward side, were about 5-15% lower than [g(h)]. Differences in g(h)/[g(h)] between ridge top and furrow bottom were smaller than differences between windward and leeward sides when wind was not parallel to the ridge orientation. Results from this research could be used to assign spatially dependent conductances from the surface to the atmosphere when modeling two or three dimensional energy and mass transport in ridge-furrow systems.