Turbulent Heat and Momentum Exchange in Nocturnal Drainage Flow Through a Sloped Vineyard

Abstract

High-frequency measurements are available at five heights within and above a row-gap trellised vineyard located on a 7$$^{\circ }$$ slope in the Southern Okanagan Valley, British Columbia, Canada. During a 3-week campaign in July 2016, approximately 17% of the nocturnal conditions exhibit drainage flow along the local slope. Drainage conditions are characterized by temperature inversions beginning around $$z/h_c = 0.39$$, where z is the height above ground level (a.g.l.) and $$h_c$$ is the canopy height (2.3 m a.g.l.), and near-surface lapses. Changes in the sign of the streamwise momentum flux suggest the presence of a jet maximum around $$z/h_c = 1.65$$, while a weak inflection point is observed near the canopy top, suggesting dynamical influences from both the drainage layer and canopy layer on the turbulent flow field. The largest observed fluxes in both the streamwise momentum flux and the turbulent sensible heat flux are near the top of the canopy, consistent with the location of the inflection point. Calculated two-point length scales from along-slope distributed temperature measurements reveal that turbulent structures are smallest near the canopy top. Conditional sampling of the three-dimensional velocity components and temperature indicate that a large fraction of canopy-layer transport is driven by canopy top turbulence, with sweeps dominating over ejections, particularly at $$z/h_c = 0.65$$.