A Psychrometer System for Micrometeorology Profile Determination

Lourence, F. J.; Pruitt, William O.

doi:10.1175/1520-0450(1969)008<0492:apsfmp>2.0.co;2

Cited by 39 publications

(13 citation statements)

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“…Periods with wind speeds less than 0.5 m/s were excluded from analysis. Air temperature and vapor pressure were determined from aspirated wet-and dry-bulb psychrometers similar to that described by Lourence and Pruitt (1969). Normally, the wind speed and temperature instruments were located at 1.0, 1.3, 1.8, and 2.8 m above the crop surface.…”

Section: Methodsmentioning

confidence: 99%

Role of transpiration suppression by evaporation of intercepted water in improving irrigation efficiency

et al. 1995

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Sprinkler irrigation efficiency declines when applied water intercepted by the crop foliage, or gross interception (Igross), as well as airborne droplets and ponded water at the soil surface evaporate before use by the crop. However, evaporation of applied water can also supply some of the atmospheric demands usually met by plant transpiration. Any suppression of crop transpiration from the irrigated area as compared to a non-irrigated area can be subtracted from Igross irrigation application losses for a reduced, or net, interception (Inet) loss. This study was conducted to determine the extent in which transpiration suppression due to microclimatic modification resulting from evaporation of plant-intercepted water and/or of applied water can reduce total sprinkler irrigation application losses of impact sprinkler and low energy precision application (LEPA) irrigation systems. Fully irrigated corn (Zea Mays L.) was grown on 0.75 m wide east-west rows in 1990 at Bushland, TX in two contiguous 5-ha fields, each containing a weighing lysimeter and micrometeorological instrumentation. Transpiration (Tr) was measured using heat balance sap flow gauges. During and following an impact sprinkler irrigation, within-canopy vapor pressure deficit and canopy temperature declined sharply due to canopyintercepted water and microclimatic modification from evaporation. For an average day time impact irrigation application of 21 ram, estimated average Igross loss was 10.7%, but the resulting suppression of measured Tr by 50% or more during the irrigation reduced Igross loss by 3.9%. On days of high solar radiation, continued transpiration suppression following the irrigation reduced Igross J. A. Tolk ([]) 9

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Section: Methodsmentioning

confidence: 99%

Role of transpiration suppression by evaporation of intercepted water in improving irrigation efficiency

et al. 1995

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“…The thermocouple junction was potted with silicone rubber in a 12-mm length of 2.5-mm outer diameter (OD) nylon tube. The wet-bulb sensor was a modification of one developed by Collins (2) similar to one of Lourence and Pruitt (9). It was made of 36-gauge, copperconstantan thermocouple wire inserted in 100-mm of 1.9-mm OD ceramic tubing sealed with silicone rubber on the end.…”

Section: Methodsmentioning

confidence: 99%

Air Temperature and Vapor Pressure Changes Caused by Sprinkler Irrigation¹

Kohl¹,

Wright

1974

Agronomy Journal

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The downwind effect of evaporation from sprinkler spray was studied in the field to determine if air temperature and vapor pressure were changed enough to influence plant growth and water use. Wet-bulb and dry-bulb temperature profiles were measured upwind and at three distances downwind from a sprinkler lateral before and during sprinkling. Wind-speed and direction were also measured. Air temperature generally was reduced less than 1 C, and vapor pressure in the air was increased less than 0.8 mb. This amount of change in the air temperature and humidity is not likely to be sufficient to cause any significant change in plant growth or evaporative loss of water. Additional index words:Evaporation loss, Evaporative cooling, Spray evaporation. S PRINKLER irrigation exposes the applied water to the atmosphere in a manner which enhances evaporation. The evaporation process cools the droplets, enabling heat to be drawn from the air through which the droplets pass, and adds water vapor to the atmosphere. The increase in atmospheric vapor pressure and decrease in air temperature caused by sprinkler irrigation are of interest in crop production because significant changes in these microclimatic variables could either benefit or retard plant growth depending on existing conditions and plant requirements. Cool-season plants growing under warm weather conditions might experience improved growth, while a warm-season crop might be retarded.In this paper, changes in vapor pressure and air temperature just above the crop surface are compared under field conditions with and without the operating sprinklers. Changes in these two parameters are directly dependent on the amount of water evaporated, a quantity often termed "evaporation loss." Generally, evaporation loss includes the evaporation from the spray plus that from the wetted foliage. Wettedfoliage evaporation under sprinkles' irrigation has been studied with full-cover crops of alfalfa (Medieago saliva L.), oats (Avena sativa L.), sudangrass [Sorghum sudanense (Piper) Stapf I , and ryegrass (Lolium multiflorum Lam.) under arid conditions with the findings that evapotranspiration from the wetted foliage was approximately equal to that from nonwetted, actively growing foliage with adequate soil moisture (1, 6, 10). Therefore, we concluded that the influence of sprinklers on air temperature and vapor pressure over a well-watered crop is mainly from spray evaporation. THEORYEvaporation of spray is difficult to measure because errors are additive in catch methods and salt concentration or electrical conductivity methods and exaggerate the estimate of evaporation. In catch methods the procedure is to measure the volume of water reaching the soil surface, subtract it from the volume applied, and call the difference "evaporation loss." However, the difference not only includes the evaporation loss from the spray, but also that from the catch device (catch cans or plastic covered area) and the mist carried beyond the measurement site, and other possible incomplete catch e...

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“…Approximately 10 to 12 cm of wick were exposed to the airstream inside the radiation shield. This design prevented conduction of heat to the sensor tip by the distilled water (Laurence and Pruitt, 1969 The measurement of temperature and humidity difTerences was achieved with the use of a reversing temperature difference measurement system (RTDMS). The basic design adopted is a modification of an earlier version of the RTDMS (McCaughey, 1981b;McCaughey and Brintnell, 1984).…”

Section: Measurementsmentioning

confidence: 99%

A radiation and energy balance study of mature forest and clear-cut sites

McCaughey

1985

Boundary-Layer Meteorol

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Components of the radiation and energy balances were measured over a clear-cut area and a mature, mixed forest during the summer of 1981 at the Petawawa National Forestry Institute, Chalk River, Ontario. The work concentrated on the clear-cut site which supported a canopy layer composed primarily of bracken fern and logging remnants.Forty days ofradiation data were collected at the clear-cut site. After the first four weeks ofmeasurements (the 'green' season), most of the ferns quickly died, and their foliage changed appearance from a green to brownish colour (the 'brown' season). The daily mean reflection coefficient of solar radiation determined over the 'green' season was 0.20 and decreased to 0.13 for the 'brown' season. The corresponding value for the forest was 0.13, based on a limited amount of data. The clear-cut site received 11% and 21% less net radiation than the forest on a 24-hr and daylight-hours basis, respectively, as a consequence of the higher reflection coefficient and larger daytime longwave radiation emission.A reversing temperature difference measurement system (RTDMS), incorporating ten-junction thermopiles was employed at each site in order to determine Bowen ratios (/I) via differential psychrometry. Both systems performed well, especially the RTDMS over the forest which was capable of resolving very small differences of temperature, typically less than 0.2 "C over a height of 3 m. The mean hourly Bowen ratio, calculated from values from 0800 to 1600 hr, varied from 0.2 to 1.0 for the forest and from 0.4 to 0.8 for the clear-cut site in the 'green' season.A significant canopy heat storage component of the energy balance, Q,, was found at the clear-cut site. In the early morning, a portion of the available energy was used to heat the biomass materials and air within the canopy layer. The stored heat within the canopy was released later in the day, increasing the available energy total.The daily mean value of the Priestley-Taylor coefficient a (Priestley and Taylor, 1972) for the 'green' season at the clear-cut site was 1.14, and individual values tended to increase during wet surface conditions and decrease when the surface dried. The daylight mean a value during dry canopy conditions at the forest was 1.05, and much higher values occurred when the canopy was wet. The enhancement of a for the wet forest was a result of the evaporation of intercepted rain (which is not limited by stomata1 resistance) and the concomitant transfer of sensible heat to the forest.

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A Psychrometer System for Micrometeorology Profile Determination

Cited by 39 publications

References 0 publications

Role of transpiration suppression by evaporation of intercepted water in improving irrigation efficiency

Role of transpiration suppression by evaporation of intercepted water in improving irrigation efficiency

Air Temperature and Vapor Pressure Changes Caused by Sprinkler Irrigation¹

A radiation and energy balance study of mature forest and clear-cut sites

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A Psychrometer System for Micrometeorology Profile Determination

Cited by 39 publications

References 0 publications

Role of transpiration suppression by evaporation of intercepted water in improving irrigation efficiency

Role of transpiration suppression by evaporation of intercepted water in improving irrigation efficiency

Air Temperature and Vapor Pressure Changes Caused by Sprinkler Irrigation1

A radiation and energy balance study of mature forest and clear-cut sites

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Product

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About

Air Temperature and Vapor Pressure Changes Caused by Sprinkler Irrigation¹