Search Results

You are looking at 1 - 6 of 6 items for

  • Author or Editor: D. A. Gillette x
  • Refine by Access: All Content x
Clear All Modify Search
Rolan D. Christofferson and Dale A. Gillette

Abstract

A method is given to estimate the shape factor (K) of the Weibull distribution directly from wind observations, without iteration, plotting, or sorting of data. The estimate is of comparable accuracy as that given by the maximum-likelihood estimate but is obtained more economically in computer time. Estimation of the scale factor (C) is done by maximum likelihood.

Full access
E. M. Patterson, D. A. Gillette, and G. W. Grams

Abstract

Simultaneous visibility observations and size-number distribution measurements of airborne soil particles were made during incidents of soil erosion in west Texas. Visibilities were calculated by applying Mie scattering theory to measured size distributions and were compared with observed visibilities. Agreement was found, and similar comparison with artifical modicications to the observed size distributions demonstrated that any major changes in the observed size distributions would result in significant discrepancies between the observed and the calculated visibilities. These comparisons confirm that under our experimental conditions the optically important particles are those in the size range 0.62 < r < 20 μm. The sensitivity of the calculated visibility to modifications in the measured size distribution implies that such comparisons between calculated and observed visibility provide a means of confirming size distribution measurements under a variety of conditions.

Full access
D. A. Gillette, R. N. Clayton, T. K. Mayeda, M. L. Jackson, and K. Sridhar

Abstract

Tropospheric aerosols from major dust storms (visibility <11 km) originating in cultivated areas of the High Plains in west central Texas and adjacent areas of New Mexico, Oklahoma and Colorado, were sampled by ground-based airturbine samplers with stacks 1 to 6 m high, by membrane filters, by airplane-borne dust samplers and by a static ground-level sampler. The particle size distributions of the aerosol dust obtained by airplane sampling fell mainly between 1 and 30 μm diameter. A bimodal size distribution occurred for the dust from ground samplers, with large concentrations in the 40 to 80 μm range as well as in the 1 to 30 μm range. The concentration of dust 2 to 5 km above the ground, measured by both the filtering and impactor methods, ranged from 0.1 to 0.4 mg m−3 for four intense dust storms in Texas during April of 1972 and 1973. The vertical flux for dust storms over the four-year period ranged from 0.25 × 10−7 to 2.2 × 10−8 g cm−2 s−1.

Oxygen isotopic ratio values of 1 to 10 μm quartz isolated from 17 dusts collected by ground-based samplers ranged from 16.4 to 19.5‰ (mean, 18.35 ± 0.77‰); three dusts from the airplane samplers averaged 18.2 ± 1.1‰. The Texas dusts arose largely from 13 wind-eroding soil mapping units and erodibility classes of sandy to clayey texture in the four states; the δ 18O values of the 1 to 10 μm quartz of these soils averaged 19.55 ± 0.28‰ (reported elsewhere). Abrasion by wind-induced inter-particle impact may have introduced a small amount of coarser quartz into the 1 to 10 μm aerosol fraction. Quartz from the coarser fractions of the dusts had δ 18O values ranging from 16.9 to 13.9‰ with the lower values applying to the preponderantly sand sizes (>53 μm). The fine silt from eroding sandy soils, derived not only from weathering but also possibly from eolian deposition, serves as a reservoir for long-range aerosol minerals, in addition to that from shales.

Full access
G. W. Grams, I. H. Blifford Jr., D. A. Gillette, and P. B. Russell

Abstract

The angular variation of the intensity of light scattered from a collimated beam by airborne soil particles and the size distribution of the particles were measured simultaneously 1.5 m above the ground. These measurements gave an estimate of the complex index of refraction m=n REn IM i of airborne soil particles, where n RE is the real part and n IM the imaginary part of the refractive index.

Standard microscopic analysis procedures were employed to determine n RE. Although a wide range of values was observed, the value 1.525 was taken as representative. By applying Mie scattering theory to each of the observed distributions of particle size, the expected angular variation of the intensity of the scattered light was calculated for a fixed value of n RE and a wide range of values of n IM. For each set of simultaneous measurements, the value of n IM was taken to be that value which provided the best fit to the experimental data. The upper limit of the value of n IM for the airborne particles studied in the experiment was determined to be 0.005 with an uncertainty factor of about 2. The estimate of n IM was found to be fairly insensitive to the assumed value of n RE.

Full access
J. J. DeLuisi, P. M. Furukawa, D. A. Gillette, B. G. Schuster, R. J. Charlson, W. M. Porch, R. W. Fegley, B. M. Herman, R. A. Rabinoff, J. T. Twitty, and J. A. Weinman

Abstract

The experimental results in Part I are used in the theoretical interpretation of the radiation flux measurements which were taken with an aircraft. The absorption term of the complex refractive index of aerosols is estimated to be approximately 0.01 for a real part of 1.5 for the wavelength bandwidth 0.32–0.68 μm. A regional variation in the refractive index is noted.

Atmospheric heating and cooling rates due to aerosol and molecular absorption in the solar and terrestrial wavelengths are determined from the radiation flux measurements. The magnitudes of these rates are compared and their relative importance is discussed.

Full access
J. J. Deluisi, P. M. Furukawa, D. A. Gillette, B. G. Schuster, R. J. Charlson, W. M. Porch, R. W. Fegley, B. M. Herman, R. A. Rabinoff, J. T. Twitty, and J. A. Weinman

Abstract

An exploratory field experiment was undertaken to determine the practicality of a method specifically designed to obtain the optical properties of aerosols as they relate to the earth's radiation balance. The method requires a basic set of data consisting of the vertical distribution of aerosol concentrations, size distribution, optical depth, and net radiation fluxes. From these data radiation absorptions are determined, and effective aerosol refractive indices consistent with the actual absorption are deduced through the application of precision radiative transfer calculations. The results of 11 experiment episodes involving a combined aircraft and surface-based measurement system are described. The episodes took place in an arid desert region located near Blythe, California, and in a semiarid agricultural region located near Big Spring, Texas. Part I deals with the physical-numerical depiction of such aerosol properties as optical depth, size distribution, and vertical profiles of concentration. Part II will deal with the analysis of measurements of the radiation field leading to the deduction of the effective aerosol refractive index compatible with the absorption of solar radiation.

Full access