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Influences of meteoric aerosol particles on the lower ionosphere
Influences of meteoric aerosol particles on the lower ionosphere
The Earth atmosphere is subject to a permanent bombardment by meteoroids which are supposed to inject extraterrestrial material into the Earth atmosphere in the order of 10 to 100 t per day when they evaporate between 80 and 110 km. The evaporated material reacts with the ambient atmosphere and recondensates into new nanometer-sized aerosol particles, so called Meteoric Smoke Particles (MSPs). The layer of MSPs coincides with the D-region ionosphere of the Earth. Here, MSPs are subject to different kinds of charging processes. Among these are, for example, the attachment of free electrons or ions to the surface of MSP and the photodetachment of electrons from negatively charged MSPs. Even secondary electron emission induced by energetic electron precipitation from within the magnetosphere is possible at polar latitudes. The aim of this thesis is to investigate how these charging processes of MSPs change the nature of the background D-region. Recent in-situ studies of the nighttime charge balance of the D-region indicate negatively charged MSPs to play a significant role. These experiments have been the starting point for modeling studies of not only the D-region charge balance but also the overall ion chemistry of the D-region. This has been accomplished by implementing a MSP size distribution for a altitude region between 50 and 100 km into the ion reaction scheme of the Sodankylä Ion and Neutral Chemistry (SIC) model. The results show, that especially the influence of MSPs on the electron density is important to characterize the D-region ion composition. During nighttime, electrons are effectively attached to the surface of MSPs resulting in reduced electron-ion recombination. Thus, the main loss process of positive water cluster ions nearly vanishes and these ions can grow to higher numbers of water ligands and also increase in number density. The capture of ions by MSPs is a significant loss process for long-lived ions only. During daytime, solar photons effectively photodetach electrons from the negatively charged MSPs. This results in a lower abundance of negatively charged MSPs during sunlit conditions. When investigating the diurnal variation of the electron density, there is a sudden drop in electron density during sunset and a sudden increase during sunrise due to the absence of/sudden onset of effective photodetachment of electrons from negative MSPs. The influence of MSPs on the ion chemistry also affects the neutral background composition through ion-neutral reactions. Especially reactive hydrogen and reactive nitrogen are affected. E.g., there are reduced abundances of reactive hydrogen at 60km altitude and of reactive nitrogen at 90 km. Similar to the ion chemistry, MSP affect the neutral composition mainly during nighttime.
Ionosphere, Ion Chemistry, Meteors, Mesosphere
Baumann, Carsten
2016
English
Universitätsbibliothek der Ludwig-Maximilians-Universität München
Baumann, Carsten (2016): Influences of meteoric aerosol particles on the lower ionosphere. Dissertation, LMU München: Faculty of Physics
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Abstract

The Earth atmosphere is subject to a permanent bombardment by meteoroids which are supposed to inject extraterrestrial material into the Earth atmosphere in the order of 10 to 100 t per day when they evaporate between 80 and 110 km. The evaporated material reacts with the ambient atmosphere and recondensates into new nanometer-sized aerosol particles, so called Meteoric Smoke Particles (MSPs). The layer of MSPs coincides with the D-region ionosphere of the Earth. Here, MSPs are subject to different kinds of charging processes. Among these are, for example, the attachment of free electrons or ions to the surface of MSP and the photodetachment of electrons from negatively charged MSPs. Even secondary electron emission induced by energetic electron precipitation from within the magnetosphere is possible at polar latitudes. The aim of this thesis is to investigate how these charging processes of MSPs change the nature of the background D-region. Recent in-situ studies of the nighttime charge balance of the D-region indicate negatively charged MSPs to play a significant role. These experiments have been the starting point for modeling studies of not only the D-region charge balance but also the overall ion chemistry of the D-region. This has been accomplished by implementing a MSP size distribution for a altitude region between 50 and 100 km into the ion reaction scheme of the Sodankylä Ion and Neutral Chemistry (SIC) model. The results show, that especially the influence of MSPs on the electron density is important to characterize the D-region ion composition. During nighttime, electrons are effectively attached to the surface of MSPs resulting in reduced electron-ion recombination. Thus, the main loss process of positive water cluster ions nearly vanishes and these ions can grow to higher numbers of water ligands and also increase in number density. The capture of ions by MSPs is a significant loss process for long-lived ions only. During daytime, solar photons effectively photodetach electrons from the negatively charged MSPs. This results in a lower abundance of negatively charged MSPs during sunlit conditions. When investigating the diurnal variation of the electron density, there is a sudden drop in electron density during sunset and a sudden increase during sunrise due to the absence of/sudden onset of effective photodetachment of electrons from negative MSPs. The influence of MSPs on the ion chemistry also affects the neutral background composition through ion-neutral reactions. Especially reactive hydrogen and reactive nitrogen are affected. E.g., there are reduced abundances of reactive hydrogen at 60km altitude and of reactive nitrogen at 90 km. Similar to the ion chemistry, MSP affect the neutral composition mainly during nighttime.