Electrodynamic structure of charged dust clouds in the earth's middle atmosphere

Abstract

Noctilucent clouds (NLCs) and polar mesospheric summer echoes (PMSEs) are two phenomena at the forefront of near-earth space science. NLCs are high-altitude clouds in the earth's mesosphere that are formed from visible aerosol particles. The occurrence rate of NLCs over time is believed to have profound implications on global climate change. NLCs are often associated with PMSEs which are strong 50 MHz–1.3 GHz radar echoes from mesospheric electron irregularities. Therefore, PMSEs may be an important remote-sensing diagnostic for the evolution of NLCs and the earth's middle atmosphere in general. The electron irregularities that produce PMSEs are generally believed to result from charging of electrons onto subvisible aerosol irregularities, the source of which is currently a debated issue. Neutral air turbulence has long been considered a primary source of the irregularities. However, there are clearly fundamental characteristics of the irregularities in past and recent observations that cannot be explained by neutral air turbulence and most probably involve plasma processes. This work considers the latter mechanism and the possibility of production of aerosol irregularities in the boundary region between the charged aerosol layer and the background mesospheric plasma. First a model for investigating the electrodynamics of this boundary layer is described. This model indicates that plasma flows are expected to exist in the electrodynamic equilibrium. An initial assessment of the possible role of these plasma flows in producing irregularities that may ultimately result in PMSEs is provided.