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R. H. Shaw

Daily values of solar and net radiation at Ames, Iowa were compared for the period, late June through November, 1954. It was found that by dividing the data into two groups, clear days and cloudy days, regression lines could be computed which fitted the data very well. The correlation between net radiation and solar radiation was 0.98 for clear days and 0.97 for cloudy days.

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H. C. S. THOM and R. H. SHAW

Abstract

A set of freeze thresholds is defined which replaces the loosely defined element “killing frost.” Freeze series are tested and found to be random. This makes it possible to fit frequency distributions. It is hypothesized that these distributions are normal and a test of significance verifies this. A hypothesis that the variance parameter is constant over Iowa is tested and found to be true. It is shown that spring and fall freeze are independent and this results in a simple form of freeze-free period distribution. The calculation of probabilities of freeze and freeze-free season are explained.

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R. H. Shaw and Paul E. Waggoner

Measurements of the diurnal and height variation of the dew-point temperature in three types of ground cover (corn, soybeans and bare ground) were made in 1948 at Ames, Iowa, using a photoelectric dew-point hygrometer. The variations are expressed as the standard deviation of a frequency distribution of the dew-point temperatures taken at half-second intervals during a minute run.

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Leo J. Fritschen and R. H. Shaw

The details of construction of a thermocouple-type anemometer and results obtained by its use in measuring the wind profile of a micro-layer, within a crop cover, are presented.

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H. Siebert, R. A. Shaw, and Z. Warhaft

Abstract

Clouds are known to be turbulent, but the details of their internal turbulent structure have been largely unexplored. Measurements of turbulent velocities in stratocumulus clouds presented here reveal an intermittent structure consistent with that observed in classic homogeneous isotropic turbulence. The measurements were taken close to cloud top in a 200-m-thick cloud layer over a path of approximately 6 km, using a hot-wire anemometer below a helicopter as part of the Airborne Cloud Turbulence Observation System (ACTOS) measurement system. Hot-wire signal artifacts resulting from droplet impacts are removed without significantly degrading the signal, such that high-order velocity structure functions can be evaluated. The structure function analysis for orders 2–8 show statistically significant departures from the Kolmogorov’s 1941 scaling, yielding scaling exponents consistent with the Kolmogorov–Obukhov refined similarity hypothesis, with an intermittency exponent of 0.25. This is in agreement with the accepted value determined in single-phase flows under carefully controlled conditions, and no evidence is found of any departure from the large body of knowledge obtained from the laboratory on the finescale turbulence structure. This suggests that processes depending on the finescale structure of turbulence that cannot presently be measured in clouds can be explored in the laboratory setting. Since these findings pertain to clouds with relatively low liquid water content and weak turbulence, further work will be required to determine their applicability to other cloud types.

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E. S. Takle, R. H. Shaw, and H. C. Vaughan

Abstract

Temperature and wind speed measurements over a 6-year period from a 32 m tower located in a primarily rural area are used to assess the pollutant-dispersive characteristics of a rural site. A monthly comparison of a crude pollution-trapping index shows July through September the most favorable, and December through February the least favorable, months for the trapping of contaminants emitted from ground-based sources in rural areas.

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M. Y. Leclerc, R. H. Shaw, G. Den Hartog, and H. H. Neumann

Abstract

This paper shows that the inclusion of thermal effects is necessary to correctly interpret the physical processes involved in the generation or suppression of Reynolds stress and turbulent kinetic energy inside a form canopy. In both of thew budgets, thermal effects are largest in the upper third of the canopy where the foliage is densest and the radiation load highest. The magnitude of the buoyant production term in both these budgets increases almost linearly with instability in the upper region of the canopy. The onset of stability exerts a strong influence on the behavior of the shear production in both the budgets of Reynolds stress and turbulent kinetic energy. In strong thermal stratification, the shear production term becomes a sink of Reynolds stress and turbulent kinetic energy in the lower half of the canopy.

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W. N. SHAW and W. H. DINES

Abstract

No Abstract Available.

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T. Schmeissner, R. A. Shaw, J. Ditas, F. Stratmann, M. Wendisch, and H. Siebert

Abstract

Helicopter-borne observations of the impact of turbulent mixing and cloud microphysical properties in shallow trade wind cumuli are presented. The measurements were collected during the Cloud, Aerosol, Radiation and Turbulence in the Trade Wind Regime over Barbados (CARRIBA) project. Basic meteorological parameters (3D wind vector, air temperature, and relative humidity), cloud condensation nuclei concentrations, and cloud microphysical parameters (droplet number, size distribution, and liquid water content) are measured by the Airborne Cloud Turbulence Observation System (ACTOS), which is fixed by a 160-m-long rope underneath a helicopter flying with a true airspeed of approximately 20 m s−1. Clouds at different evolutionary stages were sampled. A total of 300 clouds are classified into actively growing, decelerated, and dissolving clouds. The mixing process of these cloud categories is investigated by correlating the cloud droplet number concentration and cubed droplet mean volume diameter. A significant tendency to more inhomogeneous mixing with increasing cloud lifetime is observed. Furthermore, the mixing process and its effects on droplet number concentration, droplet size, and cloud liquid water content are statistically evaluated. It is found that, in dissolving clouds, liquid water content and droplet number concentration are decreased by about 50% compared to actively growing clouds. Conversely, the droplet size remains almost constant, which can be attributed to the existence of a humid shell around the cloud that prevents cloud droplets from rapid evaporation after entrainment of premoistened air. Moreover, signs of secondary activation are found, which results in a more difficult interpretation of observed mixing diagrams.

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J. H. Shaw, M. T. Chahine, C. B. Farmer, L. D. Kaplan, P. W. Schaper, and R. A. McClatchey

Abstract

Atmospheric temperature profiles, obtained from spectral radiances of the earth between 2160 and 2360 cm−1 measured by a balloonborne, multi-detector, grating spectrometer at 3.5 mb during a 6-hr flight, are described. Representative profiles obtained both before and after sunrise and for clear and cloudy skies show that atmospheric temperatures accurate to ∼2K can be inferred. The variations of surface temperature during the flight are discussed.

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