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B. B. Hicks

Abstract

Concentrations of radon daughters in falling rain have been used to derive precipitation scavenging rates of those particles with which radon daughters are associated; presumably these are the particulate component of natural, background aerosol. Scavenging rates ranging from 10−4 to 10−3 s−1 are deduced from a comparison of the observations with the predictions of simple models of in-cloud scavenging processes.

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B. B. Hicks

Abstract

A covariance computer capable of accepting analog signals representing any two atmospheric variables is described. The instrument computes the covariance in a frequency band governed at high frequencies by the sensor response times and at low frequencies by capacitive filters.

With vertical wind velocity as one input, the instrument has been successfully used for measurement of Reynolds stress, sensible heat flux, and the sum of sensible and latent heats. Given suitable sensors, direct measurement of other fluxes, such as those of CO2 and water vapor, should be possible.

The instrument is small and portable. Power consumption is ∼2 W.

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B. B. Hicks

Abstract

No abstract available.

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B. B. Hicks

Abstract

Velocity variances in the convective boundary layer are examined using data derived in PBL experiments over land (Minnesota) and ocean (the Coral Sea) supported by data from the Kansas study of the surface boundary layer. In the freely convective limit, the data clearly support scaling of σw by the convective Velocity w * instead of u *, as is common in modern treatments. The freely convective limit appears to be 0.59 for both σw/w * and σv/w *. The available data are compatible with relationships based on additive contributions to total variance by mechanical and buoyant forces. The resulting relations areThese relations collapse back to the neutral values derived from the Kansas experiment. Similar analyses for temperature variance are somewhat less revealing; however, the available data indicate that scaling by convective properties alone is quite adequate. Hence,where θ* = Hc p w *. These relations appear to apply over the bulk of the convective PBL, from z/z i ≈ 0.1 to at least z/z i = 0.6, but extend downwards to very near the surface in the case of σv

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B. B. Hicks

Abstract

The theory of condensation nucleation applied to radioactive fallout constituents shows that most tropospheric fallout particles are efficient nuclei in the production of warm rain. As a result it is found that the concentration of fallout in precipitation is a maximum soon after the onset of rain. This is supported by measurements made during many individual storms over an extensive period. The influence on fallout concentration of variations in rainfall rate through a storm is found to be complicated by the opposing effects of the liquid water content of the cloud and the generation of downdrafts within it.

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P. Hyson and B. B. Hicks

Abstract

Two instruments are described which serve as humidity sensors in conjunction with existing eddy correlation techniques. The first instrument is an infrared absorption device, with a 40 cm path length, operating in a water vapor vibrational band at 6.3 μm. The second instrument is a development of this, operating at 2.7 μm with a 20 cm path length. Both devices have been successfully field-tested in a latent heat flux format, using a propeller anemometer as a vertical velocity sensor. Satisfactory energy balances at the surface have been obtained. In the case of the 2.7 μm instrument, a specific advantage is its lack of sensitivity to ambient humidity levels, while both instruments are insensitive to slow variations of optical and electronic performance.

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Bruce B. Hicks

Abstract

Destruction of the thin subsurface thermal boundary layer at an air-water interface can be accomplished by relatively low rates of aeration and can result in substantially improved thermal performance when water temperatures are high. The heating and saturating of rising air bubbles can also provide a significant improvement in overall thermal performance when water temperatures and aeration rates are sufficiently great. At 80°C, improvements of ∼20% appear possible with average aeration rates <1 mm s−1.

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Bruce B. Hicks

Abstract

In complex terrain, horizontal advection and filtration through a canopy can add substantially to the vertical diffusion component assumed to be the dominant transfer mechanism in conventional deposition velocity formulations. To illustrate this, three separate kinds of terrain complexity are addressed here: 1) a horizontal landscape with patches of forest, 2) a uniformly vegetated gentle hill, and 3) a mountainous area. In flat areas with plots of trees, the elevation of the standard area-weighted dry deposition velocity will likely depend on the product hn 1/2, where h is the tree height and n is the number of plots per unit area. For the second case, it is proposed that the standard “flat earth” deposition velocity might need to be increased by a factor like [1 + Ra/(Rb + Rc)]1/2. For mountainous ecosystems, where no precise estimate of local dry deposition appears attainable, the actual dry deposition rate is probably bounded by the extremes associated with 1) the flat earth assumption involving aerodynamic, quasi-boundary layer, and canopy resistances as in conventional formulations, and 2) an alternative assumption that the aerodynamic resistance is zero. Such issues are of particular importance in the context of atmospheric loadings to sensitive ecosystems, where the concepts of critical loads and deposition forecasting are now of increasing relevance. They are probably of less importance if the emphasis is on air quality alone, because air quality responds slowly to changes in deposition rates. The issues addressed here are mainly appropriate in the context of air surface exchange that is not controlled by surface resistance (e.g., for deposition of easily captured chemicals such as nitric acid vapor, and perhaps for atmospheric momentum) and for chemicals that have no local sources. It is argued that dry deposition rates derived from classical applications of deposition velocities are often underestimates.

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Bruce B. Hicks

Abstract

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B. B. Hicks and J. D. Shannon

Abstract

Radioactive fallout data suggest that the concentration of pollutants in rainfall, while highly variable, might be described on the average by about an inverse half-power dependence on the amount of precipitation. Recent measurements of sulfur concentrations in summer rainfall collected at Argonne National Laboratory tend to support this contention, as do preliminary results derived from operations of the DOE precipitation chemistry network. The concept is extended to develop a bulk removal rate for airborne total sulfur by precipitation for use in regional dispersion modeling.

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