The Energy Budget at the Earth's Surface: Comparison of Momentum and Energy Balance Methods of Computing Vertical Transfer Within a Crop
AGRICULTURAL RESEARCH SERVICE ITHACA NY ITHACA United States
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Measurements of windspeed, air temperature, wet-bulb depression, and net radiation were made at several levels within and above a corn crop. Soil heat flux and incident radiation were also measured. Transfer coefficient distributions were computed separately from the windspeed data by a momentum balance approach, and from the other data by the energy balance method. The agreement between the two methods was better near the top of the crop than near the soil. Drag coefficients computed from the energy balance results were not independent of height within the crop as was assumed in the momentum balance analysis. The low Reynolds numbers for the lower portion of the crop could account for the deviation. The energy balance approach required more measurements, but was easier to apply in calculating the distribution of the transfer coefficient for the computation of the vertical flux of such entities as heat, water vapor, and carbon dioxide within the crop.