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  • Author or Editor: W. O. Pruitt x
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A. J. Dyer
and
W. O. Pruitt

Abstract

During the summer of 1961, the vertical transfer of water vapor and sensible heat was determined at a height of 4 m over an irrigated field at Davis, Calif. Simultaneous determinations of evaporation at the surface were obtained with a 20-ft weighing Iysimeter, and the corresponding sensible heat transfer computed using an energy balance approach.

A comparison of the two methods of determining these vertical fluxes showed excellent agreement early in the summer, but significant differences appeared as the season progressed. These could be attributed to severe contrasts developing between the heavily irrigated site and the surrounding areas, which, with no rain occurring, gradually dried out.

The fetch available was of the order 50–190 m depending on wind direction. The results clearly indicated that under the conditions of this experiment, the vertical fluxes were not constant with height, and a condition of horizontal uniformity did not exist.

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F. J. Lourence
and
W. O. Pruitt

Abstract

An aspirated psychrometer system using thermopiled copper-constantan sensors is described. Field data are presented showing temperature and humidity profiles obtained over a turf crop by nine self-contained units mounted on a 6 m mast. Temperature and humidity can be determined with accuracies of 0.025C and 0.15 mm Hg vapor pressure.

The units are relatively inexpensive and easy to fabricate. The wet-bulb element, a porous ceramic cup supplied with a continuous column of water from a reservoir, provides more reliable and less critical operation than the conventional cotton-wick elements.

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D. L. Morgan
,
W. O. Pruitt
, and
F. J. Lourence

Abstract

Various methods of estimating atmospheric radiation including the use of radiation charts and six empirical formulas are examined, using micrometeorological data collected at Davis, Calif. The Bolz method for adjusting the clear-sky estimates of atmospheric radiation from empirical formulas for cloudy, conditions is studied using observed cloud conditions and measured atmospheric radiation. This method works well for overcast low-cloud conditions. However, in high-cloud conditions with less than complete sky coverage, it is less satisfactory, perhaps due to problems in analytically representing the cloud conditions.

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W. O. Pruitt
,
F. Lourence
, and
Todd V. Crawford

Abstract

Several radiation components, the energy balance of a vegetative surface, and the latent heat flux from a shallow water surface were measured at Davis, Calif.,ay of the 20 July 1963 eclipse and on the following day. Both days were clear and very similar temperature, humidity and wind conditions were experienced.

The eclipse period lasted from 1135 to 1359 Pacific Standard Time. Maximum obscuration was at 1249 with 24.5 per cent of the sun's area affected (0.371 units of solar diameter). At time of maximum eclipse at Davis the total incoming shortwave, and normal incidence radiation was 24 per cent lower than at the same time on 21 July. Net radiation above a 12-cm tall perennial cover was reduced 27-28 per cent. Net radiation Just above a 2.5-cm layer of water underlain by a black polyethylene sheet was reduced 29 per cent.

Changes in weight of a very sensitive 6.1-meter diameter lysimeter indicated that evapotranspiration followed the changing pattern of net radiation quite closely during the eclipse. The percentage reduction both at 1249 and for the total eclipse period was almost the same as for net radiation. The same was true for reduction of total convective and soil heat transfer for the overall eclipse period.

A lag in response of evaporation to changing net radiation for the water surface was noted, although for the total eclipse period the per cent change of evaporation and net radiation was nearly identical.

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