The research on small-scale structures of ice particle density and electron density in the mesopause region

Abstract. In this paper, a growth and motion model is developed to investigate the evolution of radius, velocity, and number density of ice particles in mesopause region. In the growth model, meteoric dust from outer atmosphere and grains moving with the upward neutral wind from the mesosphere bottom serve as nuclei upon which water vapor can condense in the cold and moist condition. And the motion of the ice particles is mainly controlled by the gravity and the neutral drag force. It is shown that the radius of ice particles increases linearly with time. But the particle velocity has a complicated relationship with the radius due to the different mass densities of condensation nuclei and absorbed ice. For certain condensation core radius, the velocity of particles can be reversed at particular height, which leads to local gathering of particles near the boundary layer and small-scale structures of ice particle density on the order of a few meters. Based on the obtained small-scale ice particle distribution, the mean particle charge number and corresponding distributions of electrons are calculated by combining the dust charging processes and quasi-neutrality condition. It shows that the absorption of electrons by ice particles results in the formation of small-scale electron density structures, which can be important to the research on the cause of polar mesosphere summer echoes (PMSE).