Concentration and collection of meteoric dust in the atmosphere

Abstract

The size distribution of micron-sized particles in their passage through the earth's atmosphere can be significantly changed by ablation. Using the Allen, Baldwin, and James ablation model, Kornblum has calculated size and velocity histories of stony micrometeoroids, and from these particle histories the ratio of the flux at any altitude h to the entering flux, the ratio of the cumulative flux at any altitude h to the entering cumulative flux, and the ratio of the space density of particles at any altitude h to the entering space density were calculated. The radar distribution of entry velocities and random incidence were assumed for the entering flux. The space density of particles is described by a law of the form n(r) = Cr−adr, where r refers to the particle radius and C and a are constants. The flux is proportional to the space density of the particles. The values of the ratios calculated are independent of the absolute value of the entering flux, and they are found to be insensitive to changes in the value of the exponent governing the size distribution of the particles. Values of the exponent ranging from 2.8 (zodiacal light distribution) to 6.1 (early satellite data) were adopted. The above results were used to predict for various entry fluxes the meteoric dust to be expected from various balloon-borne, rocket-borne, and ground-based collectors. The collection results of the Luster sounding rocket experiments and the balloon collections of Bhandari et al. are in agreement with the predictions for low entry fluxes but not with the collection results to be expected from high entry fluxes computed from Venus Flytrap and the early satellite data. An upper limit of 1 particle/m2sec is implied for the entering flux of particles larger than 0.1 μ in diameter by the Luster II experiment. An approximate method of predicting particle collections from balloon-borne, ground-based, or sounding-rocket-borne collectors is given.