Particulate Matter in the Region 70 to 100 Km

Abstract

In his opening remarks Moderator Singer sketched present knowledge about interplanetary dust (zodiacal dust), of which the dust found in the upper atmosphere most likely is a component. Recent Al²⁶ deep-sea analyses have helped to tie down some of the important parameters. Characteristically, the dust detected by such methods is of ordinary density and stony composition, and of sizes in the 10-µ region. Taking into account the moderate estimate of daily influx of such dust (1000 tons day⁻¹) and its properties, only very low concentrations are expected in the 70–100 km region, which would not be detectable optically. Thus, high dust concentrations observed with the laser technique and in noctilucent clouds with the sun as a light source may be indicative of strong atmospheric motions. Dust in the upper atmosphere, therefore, may be of particular interest to those studying the dynamics of the atmosphere in that region. Singer also pointed out some physical and chemical functions which dust may perform in the region, such as acting as nucleation centers. Fiocco elaborated on this, suggesting that on the basis of even the moderate influx cited above, enough ionization would be produced to account for the electron concentration at night in the E-layer.

A detailed report submitted by S. K. Poultney served as background for a portion of this summary.