Studies of the MLT/I using Multistatic Meteor Radar

Abstract

This thesis applies a multistatic meteor radar to an investigation of the dynamics of the mesosphere lower thermosphere/ionosphere (MLT/I; 60-110 km altitude). The main radar used in the study operates at 55 MHz and is in the vicinity of Adelaide, South Australia, consisting of a monostatic radar at the Buckland Park eld site (34.6 S, 138.5 E) and a bistatic receiver located about 55 km south-east at a site in the Adelaide Hills (35.1 S, 138.8 E). The areas of investigation pertaining to MLT/I dynamics include assessing the ability of a multistatic meteor radar to measure the vertical ux of horizontal momentum and studying the interaction between gravity waves and tidal e ects. The thesis also presents a novel phase calibration technique for meteor radars, based on the use of civilian aircraft. The assessment of this radar's ability to measure MLT/I momentum uxes demonstrated that a relative uncertainty of about 75% can be expected for a monostatic con guration, assuming a ux magnitude of 20 m2s-2, a single day of integration, and a gravity wave field synthesized from a realistic spectral model. The multistatic configuration with a single bistatic receiver is shown to yield a relative uncertainty of about 65% under the same conditions. It is suggested that the increase in precision can be attributed entirely to the increase in the number of meteor detections associated with the combined monostatic and bistatic receivers, rather than due to the existence of a more favourable distribution of Bragg vectors arising from the receiver separation. A case study of winds around the autumnal equinox of 2018 revealed large modulations in diurnal tidal amplitudes, with peak component diurnal tide amplitudes of 50 ms-1 and peak zonal wind velocities of 140 ms-1. In the context of the need to verify the accuracy of momentum ux estimates from the radar, this motivated an investigation into the role momentum transport from gravity wave breaking played in modulating the tidal amplitudes. The investigation showed that while the observed gravity wave forcing exhibited a complex relationship with the tidal winds, the components of the forcing were generally seen to be approximately out of phase with the tidal winds above altitudes of 88 km. Additionally, no clear phase relationship between the tides and gravity wave forcing was observed below 88 km. Following the case study, the altitude and angle-of-arrival (AOA) errors and reduced meteor detection rates associated with suspected receiver phase calibration errors motivated the development of an alternative phase calibration technique. The technique developed was based on the use of echoes from civilian aircraft with known positions. Approximately two weeks worth of aircraft detections with the radar and a 1090 MHz Automatic Dependent Surveillance Broadcast receiver (used to receive aircraft position information) was acquired during November 2019. By taking into account the implied phase correction variability with AOA using a beamforming approach, it was shown that the aircraft-based corrections yielded an equal or smaller meteor height distribution width than the conventionally used empirical phase calibration technique. Assuming that a smaller height distribution width equates to smaller average height estimation errors, this was taken to mean that the aircraft-based approach outperformed the empirical one.