Investigation into the photon interaction of small mesospheric dust and its impact on the ionospheric charge balance

Abstract

This thesis investigates the charging mechanisms of nano-sized meteoric smoke particles (MSP) in the mesosphere, with a particular focus on the photoionization and photodetachment processes on MSP assuming different materials. The study begins with three theoretical chapters that lay the ground- work for understanding relevant topics like the atmospheric region in question, MSP, the solar spectrum, light scattering, Mie theory, and charging processes of MSP. Subsequently, computational simulations are made to explore how photoionization and photodetachment is affected by different parameters like MSP material properties and solar irradiation and how photoionization and photodetachment affect the charge states of MSP by varying MSP material and ionospheric properties.

The model calculations carried out in this thesis indicate that while photoion- ization and photodetachment do impact MSP charge states, their effect may not be as significant as previously thought. The models suggest that a fraction of sub-nanometer sized MSP between 15 and 40% can remain negatively charged, and that larger MSP with 𝑟 > 1 nm have a chance of being positively charged. Material properties like refractive index and work function play a crucial role in affecting the photoionization of MSP, which subsequently affect the charge state of MSP, underscoring the need for more experimental data on the optical properties of possible MSP materials.