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Gerald W. Grams

Since the early 1960s, the development of atmospheric probing instrumentation that incorporates lasers has led to a variety of techniques for observing the atmosphere. The number of laser atmospheric studies has steadily increased since the time in 1963 when Fiocco and Smullin at the Massachusetts Institute of Technology reported the first laser measurements of atmospheric properties—laser echoes from dust layers in the upper atmosphere. Since that time, tropospheric, stratospheric, and mesospheric dust concentrations, gaseous pollutant concentrations, cloud heights and thicknesses, and wind velocities are among the many characteristics of the atmosphere that have been observed quantitatively with laser probes.

This review will describe some of the laser-atmospheric interactions that have been exploited to measure specific atmospheric properties, the extent to which those concepts have been applied, and some views regarding future applications of laser probes for observing the atmosphere.

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Philip B. Russell
and
Gerald W. Grams

Abstract

Several analytical models of the radiative effects of aerosol layers on global climate provide the common result that the critical value (ρc ) of the ratio (ρ) of aerosol layer absorption to hemispheric backscattering is given by
ρ c A2A
where A is taken to be the albedo of the earth's surface, or of the present earth–atmosphere system. The models predict that introduction of a new aerosol layer with ρ > ρ c will cause a decrease in system albedo, and a layer with ρ < ρ c will cause an increase. In this paper we demonstrate this common result for &rho c and then employ recently published data on the complex refractive index and size distribution of atmospheric surface layer soil particles to compute values of ρ. The resulting values (5 < ρ < 28) are quite large compared to previous estimates. Together with the above model result they indicate that increased generation of such airborne soil particles will tend to increase the input of solar energy to the earth–atmosphere system. This “heating” effect results, in part, from the relatively large mean particle sizes used in the computations. The effects of particle asphericity on the computed ρ values are discussed.
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