Estimation of Sensible Heat Flux Density and Latent Heat Flux Density in Vineyards Located on Hillside Terrain Using Calibrated Surface Renewal Analysis

Résumé du livre

Sensible and latent heat flux densities were estimated in a level vineyard, a northeast aspect vineyard and a southwest aspect vineyard in the Napa Valley of California using the eddy covariance and surface renewal methods. Surface renewal makes estimates of sensible heat flux density by analyzing ramp-like patterns in air temperature associated with coherent air parcels that interact directly with the crop surface in a regular manner. Surface renewal is theoretically not limited to level or extensively homogeneous terrain because it examines a more localized process of scalar exchange as compared with eddy covariance. Surface renewal estimates must be calibrated against eddy covariance data to account for apparent unequal heating of the air parcels under a fixed measurement height. We calibrated surface renewal data against eddy covariance data in a level vineyard and the calibration factor ([alpha]) was applied to the surface renewal measurements on the hillside vineyards. All three vineyards had similar row spacing, row orientation to the prevailing wind direction, and canopy architecture, so [alpha]; was assumed to be the same for all three sites. Latent heat flux density was estimated from the residual of the energy balance. The latent heat flux density was divided by the latent heat of evaporation to obtain the mass flux density of water vapor, and the mass flux density of water vapor was converted to hourly and daily actual evapotranspiration. In the level vineyard, the average daily actual evapotranspiration for the period of June through September was 2.4 mm per day. In the northeast aspect vineyard, the average daily actual evapotranspiration was 2.2 mm per day, while in the southwest aspect vineyard it was 2.7 mm per day. The net radiation values for the level vineyard, the northeast aspect vineyard, and the southwest aspect vineyard were compared against the ECOWAT model with good agreement.