Mesospheric winds above the South Island of New Zealand
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
This project involved the comparison of horizontal winds from three different techniques in the upper mesosphere, lower thermosphere region at 80-105 km and the characterization of the ability of the Fabry-Perot technique to observe gravity waves in the airlow layers. The wind measurements for the comparison were obtained by three independent ground-based techniques, a meteor radar (MR), a medium frequency radar (MF) and an optical Fabry-Perot spectrometer (FPS). All three instruments are located on the South Island of New Zealand. The optical winds were derived from night-time observations of the Doppler shifts in the mesospheric 840 nm hydroxyl emission near 87 km and the lower thermospheric 557.7 nm atomic oxygen emission at about 95 km height. The radar winds were obtained using a partial reflection medium frequency radar operating at 2.4 MHz and a meteor radar operating at 26.2 MHz with a pulse repetion rate of 379 Hz. The initial comparisons were made for 5 consecutive nights during May 1997. As a consequence of the results obtained the comparison of the FPS/MR combination were extended to 80 nights in the period encompassing May 1997 to April 1995. Dates considered suitable were those exhibiting no cloud and low magnetic activity. A very good correlation was observed between the FPS and MR winds for the 5 consecutive days and, albeit to a lesser degree, in the complete data set of 80 days. The good correlation between the FPS and the MR was used to determine the monthly mean height of the hydroxyl and the atomic oxygen layer over the period between May 1997 to April 1995. The result shows an annual variation in the height of the hydroxyl layer with the lower height during early summer and little variation in the height of the atomic oxygen layer. The study of the detectability of the gravity waves in the FPS wind measurements reveals that waves from the part of the gravity wave spectrum which shows the most activity can only, if at all, be detected with a strongly attenuated amplitude. With knowledge of the gravity wave detect ability of the FPS, signatures of very long wavelength gravity waves were sought in the available data set. On many nights signatures of wave activity which could be related to gravity waves were found. The attempt to use the MR data set to aid in the determination of the wavelength of those waves was of limited success.