On the problem of retrieving mesospheric temperature from radio meteor echoes

This thesis provides details of the fundamental research I have conducted on radio meteors using a VHF interferometric radar. An interdisciplinary approach at the intersection between radio science, astronomy, theoretical physics and statistical methods was adopted in all aspects of this thesis. The study covered key areas in meteor science, from the classical ablation theory describing the meteoric ionisation in Earth’s atmosphere to their astronomical properties, but also the formation of meteor echo signals at the radar receiver and an extensive system analysis of the instrument being employed. The central problem that this thesis has attempted to understand is why there is a persistent failure of meteor radar to measure the correct mesospheric temperature, especially in the context of high latitude observing stations.

The main scientific results of this thesis can be broadly divided into two parts: a theoretical and an application. In paper II, the theory of radio meteor height distribution was re-formulated into a simpler analytical form. It was shown that the width of radio meteor height distribution, in unit of atmospheric scale height, is inversely related to effective mass index of the meteors being sampled by the radar. This latter quantity is the calibration factor that is needed to correct for the velocity-dependent sensitivity variation in radar sampling, while the constant of proportionality of this inverse relation was found to be consistent with the 1954 theoretical prediction made by T.R. Kaiser. In Paper III, a novel method of retrieving mesospheric temperature from radio meteor height distribution was presented.

Paper I reviewed the traditional method of temperature/scale height measurement from the presumed height-dependence of the diffusion coefficient. A statistical analysis revealed a substantial lack of linear correlation contrary to what the first-order scattering theory predicts. The reasons for such broad dispersion was investigated in details in this thesis by taking into account of various selection effects in radar sampling, as well as re-assessing the meteor echo signal analysis.