Doctor of Philosophy
Meteors with peak magnitudes fainter than +2 are typically called faint meteors, resulting from the atmospheric entry and ablation of meteoroids less massive than 10-4 kg. The processes of luminous wake formation and fragmentation, which occur during ablation, are poorly understood for faint meteors, and are important constraints for models of meteoroid structure. The goal of this work is to improve understanding of these processes through analysis of high-resolution intensified video observations, and creation of a detailed meteoroid ablation model.
In the first part of this work, thirty faint meteors observed with the Canadian Automated Meteor Observatory (CAMO) are analysed, revealing meteor trails with widths up to 100 m at heights above 110 km. These widths vary with height as the inverse of the atmospheric density, suggesting that formation of the wake is related to collisions between evaporated meteoric atoms and atmospheric molecules.
Next, nine fragmenting faint meteors captured with CAMO are examined. Fragments from eight of the nine meteors are found to have transverse speeds up to 100 m s-1. These speeds are not explained by aerodynamic separation theory typically used for brighter meteors that fragment at lower heights. Instead, fragment separation by rotational breakup of the meteoroid or electrostatic repulsion are considered, giving meteoroid strength estimates up to 1 MPa. These strengths are typical of meteorite-producing meteoroids and are larger than expected for small meteoroids.
Finally, a single-body ablation model, based on modelling collisions between the meteoroid, meteoric atoms, and atmospheric molecules, is devised to explain wake formation. Synthetic meteor trail widths and lengths, as well as light curves and deceleration profiles, are compared to observations of nine meteors from the first part of this thesis. The widths of simulated meteor wakes show good agreement with observations, but simulated wake lengths are too short. This suggests that collisional de-excitation of meteoric particles is a plausible process for wake formation, but also that meteoroid fragmentation likely increases the length of the meteor wake. Compared to observations, simulated light curves are longer, and simulated meteoroids experience less deceleration, suggesting that meteoroid fragmentation should be investigated in the next iteration of the model.
Stokan, Edward, "Fragmentation and Wake Formation in Faint Meteors: Implications for the Structure and Ablation of Small Meteoroids" (2014). Electronic Thesis and Dissertation Repository. 2581.