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Published online 1 September 1967
Published in Agron J 59:427-432 (1967)
© 1967 American Society of Agronomy
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Comparison of Momentum and Energy Balance Methods of Computing Vertical Transfer Within a Crop1

J. L. Wright and K. W. Brown2

Measurements of windspeed, air temperature, wet-bulb depression, and net radiation were made at several levels within and above the 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.

Key Words: exchange coefficient • wind profile • temperature profile • humidity profile • drag coefficient

1 Contribution from Northeast and Northwest Branches, Soil and Water Conservation Research Division, Agricultural Research Service, USDA, in cooperation with the New York State Agr. Exp. Sta. at Cornell University (Department of Agronomy Paper Series No. 733). The work was supported in part by the Atmospheric Sciences Research Division, U. S. Army Electronics Research and Development Activity, Fort Huachuca, Ariz. Presented by the senior author at the 1965 Annual Meeting of the ASA, Oct. 31-Nov. 5, 1965, at Columbus, Ohio.

2 Research Soil Scientist (Physics) Snake River Conservation Research Center, Kimberly, Idaho (formerly located at Ithaca, N. Y.), and Research Assistant, University of Nebraska (formerly Research Assistant, Cornell University, Ithaca, N. Y.)

Received for publication March 8, 1967.


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Copyright © 1967 by the American Society of Agronomy.