The effect of row orientation on below-canopy turbulence characteristics in a wine-vineyard

The momentum flux affects the energy exchange processes and thus may indirectly affect the water balance of agricultural fields. In wine vineyards, a high momentum flux between the vine rows may augment the evaporation and transpiration fluxes, and therefore decrease the water use efficiency. On the other hand, at night, high momentum fluxes may reduce (or even prevent) the formation of dew on the vine canopy, thus decrease the potential development of fungi and related diseases. We hypothesized that the wind direction relative to the row orientation in largely-spaced narrow hedge-rows characterizing wine vineyards greatly affects the turbulent structure and the momentum flux. This, in turn affects the vineyard microclimate, and ultimately, the grape quality. The objective of our research was to explore the effect of wine-vineyard row orientation on wind and temperature profiles below (and slightly above) the canopy and on the turbulence characteristics and eddy size.  The research was conducted in two adjacent vineyards in the Judean foothills in Israel (31°48'38.6"N 34°50'43.6"E and 31°48'37.1"N 34°50'24.0"E) having row orientations of NE-SW and SE-NW, respectively. With a NW prevailing wind direction, the wind is typically flowing perpendicularly to the former and in parallel to the latter. In each vineyard, 10 self-made type-T fine-wire thermocouples (0.08 mm diameter) were set on a pole places in the middle of the inter row, at heights above the ground of 5, 10, 20, 40, 80, 140, 220, 250, 300, and 400 cm. In addition, 4 fast-response 2D sonic anemometers were set at 10, 40, 140, and 250 cm above the ground. The measurements were conducted at 20 Hz.  Below canopy wind regime differed with orientation, mostly at heights lower than 2.5m. Higher wind speed below the canopy and smaller wind speed gradients were observed at the vineyard parallel to the prevailing wind direction.  Temperature gradients were mostly larger in the vineyard perpendicular to the prevailing wind direction.  Nevertheless, the power spectra were generally more uniform in height at the perpendicular vineyard.