Equilibrium temperatures of small particles in the Earth's upper atmosphere (50–110 km)

Abstract

Aerosols absorb radiation from the solar and planetary radiation fields, exchange sensible heat by collisions with the ambient gas, and emit thermal radiation. If changes in phase are possible, they also lose or acquire latent heat. As a result of equilibrium between source and loss terms, particles acquire a temperature T p that can be substantially different from the ambient gas temperature T g∗ Differences T p − T g , in excess of 100 K are obtained above 60 km in daytime, depending on size, refractive index, and planetary albedo; negative differences can be obtained at night. The relative contribution of the energy exchange terms also varies; in particular, the fraction of absorbed radiation transferred into the ambient gas by collisions changes significantly with particle size and altitude. The attainment of high T p 's may have important consequences in several upper atmospheric phenomena, such as the sublimation of alkali metals ( Fiocco and Visconti, 1973), the formation of noctilucent clouds, and other surface-related effects. The dependence of the heating rate, characterizing the exchange of energy between particles and gas, on various factors such as the planetary albedo may have a bearing on upper atmospheric behavior when sufficient particle concentrations exist.