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  • Author or Editor: B. B. Hicks x
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B. B. Hicks and H. S. Goodman

Abstract

A system is described for the measurement of the atmospheric flux of water vapor near the surface, using a quartz-crystal oscillator as humidity sensor (as described by Gjessing et al.) and based on the Fluxatron technique. Results from a field test give an energy balance recovery ratio (LE + H)/(RG) = 1.00 ± 0.04.

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B. B. Hicks and R. G. Everett

Abstract

No abstract available.

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B. B. Hicks and R. T. McMillen

Abstract

“Eddy accumulation” is a variation of standard eddy correlation techniques for determining eddy fluxes by sampling air in two separate systems depending on whether the vertical velocity is positive or negative. In concept, the corresponding eddy flux is determined directly from measurements of the pollutant concentration (or accumulation) difference between the two sampling systems. In practice, the method has not yet been demonstrated for a slowly-depositing pollutant.

A numerical simulation of the eddy accumulation technique has been used to test the sensitivity of the method to errors arising from various sources, including sensor orientation, sampling limitations and chemical resolution. These tests were conducted using artificial pollutant concentration signals derived from real meteorological data (obtained above a forest canopy), in order to avoid the possibility of injecting unwanted errors by employing a poor quality pollutant signal. To detect a pollutant deposition velocity of 0.1 cm s−1, it appears necessary to maintain linear sampling characteristics over a dynamic range corresponding to two orders of magnitude of vertical wind speed (the limits are approximately 0.05 σw and 5σw in any given condition, where σw is the standard deviation of the vertical velocity w), to maintain sampling zero offsets to less than 0.02σw of equivalent vertical velocity and to resolve chemical concentration differences amounting to about 0.4% in typical conditions.

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Marvin L. Wesely and Bruce B. Hicks

Abstract

Temperature and humidity fluctuations at frequencies within the inertial subrange are found experimentally to be partially correlated in the surface boundary layer over warm wet surfaces. The spectral correlation coefficient, deduced from variances and covariances computed by analog electronics, is near unity in the flux-carrying eddies and decreases with increasing frequency, approximately as n½. As a result, optical refractive index fluctuations may have the false appearance of being strongly anisotropic in the inertial subrange.

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J. R. Garratt, B. B. Hicks, and R. A. Valigura

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A. J. Dyer, B. B. Hicks, and V. Sitaraman

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A. J. Dyer, B. B. Hicks, and V. Sitaraman

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A. J. Dyer, B. B. Hicks, and K. M. King

Abstract

As a result of experience gained with the Evapotron in the measurement of eddy fluxes, a new instrument called the Fluxatron has been developed. The computing efficiency has been improved by filtering out slow eddies which do not contribute to the eddy flux.

The Fluxatron employs a propeller anemometer to detect the vertical wind component, and the response time of this device (0.3 sec) is suitable for measurements to be made at a height of 4 m. Only 2 W of battery power are consumed, in contrast to the Evapotron which uses 50N–100 W.

The new instrument is extremely simple to operate in the field, and is thus suitable for use by relatively unskilled personnel.

In its present form, the Fluxatron measures only sensible heat transfer. The measurement of the evaporative flux presents no difficulty in principle, but it is hoped that an alternative humidity sensor may be found other than a fine-wire wet bulb as in the Evapotron.

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B. B. Hicks, P. Hyson, and C. J. Moore

Abstract

Eddy correlation instruments mounted above a plantation of Pinus radiato near Mt. Gambier, South Australia, have been operated during two periods of intensive effort, in May and October, 1972. Measurements of the Reynolds stress and of wind speed gradients show that the zero plane for momentum is located at about d = 0.8h (where h is the height of the trees), and that the roughness length of the surface is about 30% of the difference (hd).Sensible heat fluxes and temperature gradients give a displacement length not significantly different from that applicable in the momentum case, but the roughness length for sensible heat transfer is smaller than that for momentum, by about a factor of 3.Advective effects are found to be important, particularly when the fetch across the canopy is less than about 0.8 km (corresponding in our case to an effective fetch/height ratio of between 100 and 200). Long-fetch cases allow an evaluation of the heat storage (S) in the canopy and in the air below the height of eddy flux measurement. The rate of heat storage is found to be about 60 ± 20 W m−2 per °C h−1 of canopy temperature change (for a densely packed forest with trees about 13 m high), which is compatible with measurements of the biomass and assumed specific heats. The residual heat energy at about 6 m above the effective zero plane, unaccounted for by the various measured fluxes, is found to be related to the difference in net radiation over grassland and forest.During daytime, the forest is found to lose heat by turbulence in much the same manner as pasture, with fluxes of similar magnitude (although possibly differing to the extent of differences in ground flux, albedo and emissivity, for example) and giving similar Bowen ratios. At night, however, the evaporation from the forest tends to continue as heat is supplied by the cooling canopy. This is in direct contrast to the usual situation over pasture, where the heat storage is not of sufficient magnitude to result in this behavior.

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R. L. Hart, F. R. George, L. S. Vanloon, B. B. Hicks, and F. C. Kulhanek

Abstract

A new radiosonde system considerably improves the detection of fine temperature structure in the lower atmosphere. Special features of the system include a simple, inexpensive radiosonde which uses a monolithic timer in a rapid-response, temperature sensing audio oscillator circuit, a receiver which uses an integrated-circuit phase-lock-loop to track the audio-frequency pulses, and a simple, barometric release mechanism. The system has been used extensively in recent field investigations of the planetary boundary layer.

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