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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

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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

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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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B. B. Hicks, J. J. DeLuisi, and D. R. Matt

This paper describes a new radiation monitoring program, the Integrated Surface Irradiance Study (ISIS), that builds upon and takes over from earlier NOAA networks monitoring components of solar radiation [both the visible component (SOLRAD) and the shortwave component that causes sunburn, UV-B] across the continental United States. ISIS is implemented in two levels. Level 1 addresses incoming radiation only, and level 2 addresses the surface radiation balance. Level 2 also constitutes the SURFRAD (Surface Radiation) program of the NOAA Office of Global Programs, specifically intended to provide radiation data to support large-scale hydrologic studies that will be conducted under the Global Energy and Water Cycle Experiment. Eventually, it is planned for level 2 sites to monitor all components of the surface energy balance. Both levels of ISIS will eventually measure both visible and UV radiation components. At present, there are nine sites that are considered to be at ISIS level 1 standard and an additional four level 2 SURFRAD sites. A 10th level 1 site will be in operation soon. Plans call for an increase in the number of sites of both kinds, up to about 15 ISIS sites, of which 6 will be at the SURFRAD level. Data are available via FTP at ftp.atdd.noaa.gov/pub/isis or at http://www.srrb.noaa.gov (level 2).

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J. M. Hales, B. B. Hicks, and J. M. Miller

Three demands for wet-deposition data and dry-deposition data are particularly important at the present time: 1) the analysis of long-term trends to evaluate the consequences of emission changes, 2) the measurement of deposition loadings to determine impacts to receptors, and 3) model development and the analysis of atmospheric source-receptor phenomena. The diversity of these demands has led to deployment of a variety of networks to satisfy different measurement requirements. Consideration of this diversity of network goals has led to a distinction between research-oriented networks and routine measurement networks. Research-oriented networks generally contain a comparatively small number of stations, and make relatively intensive measurements with fine time resolution, to focus on relevant processes. These networks use relatively advanced measurement techniques and require much-greater scientific attention than routine measurement networks. Routine networks usually have a greater number of simpler stations to provide finer spatial resolution, but have a coarser time resolution; they yield a more-descriptive picture of wet and dry deposition over periods of weeks or months. Both types of networks have their place in the overall measurement effort. In this paper, the relationship between existing research arrays and routine-measurement arrays is discussed, and a rationale is suggested for operation of the research arrays—the Multistate Power Production Pollution Study (MAP3S) (for wet deposition) and COre Research Establishment (CORE) (for dry deposition) research measurement networks.

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

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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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Farn Parungo, Joe F. Boatman, Stan W. Wilkison, Herman Sievering, and Bruce B. Hicks

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A statistical analysis using published data on the global distribution of total cloud cover and cloud type amounts over the ocean, reduced from the Comprehensive Ocean–Atmosphere Data Set (COADS), shows a significant positive trend (4.2% increase from the 1930 baseline) in total oceanic cloud amount in the period between 1930 and 1981. The increase of total cloud amount for the Northern Hemisphere (5.8% ) was twice that for the Southern Hemisphere (2.9% ), The more consistent 30-yr ( 1952–1981 ) data show that the change in cloud amount ( 1952 base) was 1.5% for the globe, 2.3% for the Northern Hemisphere, and 1.2% for the Southern Hemisphere. The analysis also shows that the greatest cloud amount increase was for altocumulus and altostratus clouds and that this increase was most pronounced at midlatitudes (30°–50°N). The trend and the pattern of cloud amount variations appear to be in accord with the temporal trend and geographic distribution of S02 emissions. It is hypothesized that sulfate particles converted from S02, may modify cloud droplet spectra, causing affected clouds to be more colloidally stable than unaffected clouds. The longer residence times of affected clouds could cause increases of cloud frequency and cloud amount.

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Bruce B. Hicks, William J. Callahan, William R. Pendergrass III, Ronald J. Dobosy, and Elena Novakovskaia

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The utility of aggregating data from near-surface meteorological networks for initiating dispersion models is examined by using data from the “WeatherBug” network that is operated by Earth Networks, Inc. WeatherBug instruments are typically mounted 2–3 m above the eaves of buildings and thus are more representative of the immediate surroundings than of conditions over the broader area. This study focuses on subnetworks of WeatherBug sites that are within circles of varying radius about selected stations of the DCNet program. DCNet is a Washington, D.C., research program of the NOAA Air Resources Laboratory. The aggregation of data within varying-sized circles of 3–10-km radius yields average velocities and velocity-component standard deviations that are largely independent of the number of stations reporting—provided that number exceeds about 10. Given this finding, variances of wind components are aggregated from arrays of WeatherBug stations within a 5-km radius of selected central DCNet locations, with on average 11 WeatherBug stations per array. The total variance of wind components from the surface (WeatherBug) subnetworks is taken to be the sum of two parts: the temporal variance is the average of the conventional wind-component variances at each site and the spatial variance is based on the velocity-component averages of the individual sites. These two variances (and the standard deviations derived from them) are found to be similar. Moreover, the total wind-component variance is comparable to that observed at the DCNet reference stations. The near-surface rooftop wind velocities are about 35% of the magnitudes of the DCNet measurements. Limited additional data indicate that these results can be extended to New York City.

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Bruce B. Hicks, William R. Pendergrass III, Christoph A. Vogel, and Richard S. Artz

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Data from a network of micrometeorological instruments, mostly mounted 10 m above the roofs of 12 buildings in Washington, D.C., are used to derive average values and spatial differences of the normalized local friction velocity u */u ≡ ()1/2/u (with u being the wind speed reported at the same height as the covariance is measured, w being the vertical wind component, primes indicating deviations, and the overbar indicating averaging). The analysis is extended through consideration of two additional sites in New York City, New York. The ratio u */u is found to depend on wind direction for all locations. Averaged values of u */u appear to be best associated with the standard deviation of local building heights, with little evidence of a dependence on any other of the modern building-morphology indices. Temperature covariance data show a large effect of nearby activities, with the consequences of air-conditioning systems being obvious (especially at night) in some situations. The Washington data show that older buildings, built largely of native limestone, show the greatest effects of air-conditioning systems. The assumption that the nighttime surface boundary layer is stable is likely to be most often incorrect for both Washington and New York City—the sensible heat flux resulting from heating and cooling of building work spaces most often appears to dominate.

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