Search Results

You are looking at 1 - 4 of 4 items for :

  • Author or Editor: R. G. Pinnick x
  • Journal of Applied Meteorology and Climatology x
  • Refine by Access: All Content x
Clear All Modify Search
Peter Chýlek, R. G. Pinnick, and V. Srivastava

Abstract

The radar backscattering cross sections of spongy hailstones are considerably influenced by the topological structure of the water-ice mixture. Observational evidence suggests that such an inhomogeneous composite medium can consist of regions of different topologies. We investigate three different kinds of topologies and derive a general mixed topology mixing rule (MTMR). The mixed topology rule is used to calculate the effective dielectric constant of spongy ice as a function of its liquid-water content. This leads to predictions of backscatter cross sections that are in good agreement with measurement.

Full access
Peter Chýylek, Peter Damiano, Dat Ngo, and R. G. Pinnick

Abstract

We have developed a simple approximation for the absorption, extinction and scattering coefficients, infrared emittance, single-scattering albedo, and asymmetry factor of water clouds within the 8–12-μm spectral region. The aforementioned cloud-scattering characteristics are obtained as continuous functions of the wavelength λ liquid water content W, effective r eff, and effective v eff of the droplet-size distribution. The accuracy of the proposed approximation is shown to be within 6% for the most types of water clouds when compared to the exact Mie theory calculation and integration over the size distribution. At the same time the required computer time is reduced by factor of 102–103.

Full access
R. G. Pinnick, D. M. Garvey, and L. D. Duncan

Abstract

Measurement of cloud drop size distributions with the Knollenberg model FSSP-100 light-scattering counter can lead to artificial bumps or knees in the distributions at ∼0.6 μm and sometimes 2–4 μm radius if the manufacturer-supplied calibration is used. These artifacts are a consequence of the instrument having multivalued or slowly changing response in these regions of particle size. A modified calibration procedure is given that removes these artifacts so that the true droplet size distribution can be obtained. Measurement of slightly nonspherical particles with refractive indexes characteristic of those of atmospheric aerosols will generally lead to undersizing if the FSSP manufacturer-calibration is used, but likely by not more than a factor 2.

Full access
C. W. Bruce, Y. P. Yee, B. D. Hinds, R. J. Brewer, J. Minjares, and R. G. Pinnick

Abstract

A field adapted spectrophone system employing a tuneable CO2 laser source (over wavelengths 9.2–10.8 μm) was used to measure atmospheric gaseous and particulate absorption at an isolated desert location in the southwestern United States. Measurements were made both for ambient conditions (when aerosol particulate absorption was found to be negligible compared to that of gases) and for dusty conditions resulting from vehicular traffic. For ambient conditions the gaseous absorption coefficient was found to vary with time from expected levels upward by as much as a factor of 3. Sources which could be correlated with increased absorption are discussed. For dusty conditions the spectrophone data were compared with estimates of the absorption coefficient calculated on the basis of measured particle size distributions together with estimates of particle complex indices of refraction. Temporal variation of the absorption coefficient correlated quite closely for the two methods while the calculated values were generally higher. Sampling and calculational uncertainties are suggested as likely to be responsible for this discrepancy.

Full access