On the formation of electron depletions at the summer polar mesopause

Abstract

In the summer polar mesopause region, rocket and radar observations have revealed layers of deep electron depletions for which electron scavenging by ice particles with sizes less than 10 nm appears to be the most plausible explanation. The lack of significant ion depletions and the absence of any relationship between the occurrence of polar mesospheric clouds and auroral activity suggest that the ice particles are generated by heterogeneous nucleation on meteoric dust. Then the Kelvin effect, predicting an increase of the equilibrium water vapor pressure with decreasing particle radius, strongly affects the formation of electron depletions. In particular, weak perturbations of the temperature and water vapor concentration associated with small‐scale internal gravity waves can produce time‐dependent multiple layer structures with steep gradients characterized by length scales of a few hundred meters, in good agreement with observational results.