Diffusion of meteoric plasma
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
A summary of the present understanding of the behaviour of meteoric ionization is given and cooling times for meteoric particles are calculated. While the cooling time for neutral atoms and positive ions is short compared to echo life-times, that for electrons is not and thermalization effects may be observed above 100 km. The effect of winds and sky noise on diffusion coefficient measurements has been investigated and it appears that the scatter in measurements predicted accounts for that observed in practice. A magnetic effect on meteor train diffusion has been observed in underdense meteors by using a backscatter radar, with a 40 kW pulsed transmitter operating at 26.36 MHz. Echo heights were measured with a spaced interferometer. The observed magnetic effect is consistent with that expected from the formation of electron and ion ellipses of ionization. Other results recorded when anisotropic, ambipolar diffusion is more likely do not show this effect. Previous observations, limited to overdense meteors, are shown to be consistent with theoretical predictions and the expected magnetic effects on diffusion for general train orientations are discussed. Phase variations caused by Fresnel diffraction as meteor trains are formed have been studied and shown to be a cause of systematic decreases in echo heights (during the lifetime of an echo) measured with spaced antennas. An experiment to verify this is suggested. A chemical model developed to take into account ionization loss may account for anomalously high D values below 90 km observed in previous data. High D values measured in this work cannot be explained by this simple model.