Date of Award
1996
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Abstract
This thesis focuses on the experimental investigation of large- and medium-scale dynamics in the 70-100 km height range measured with MF (2.219 MHz) and meteor VHF (40.68 MHz) radar systems located at London (43{dollar}\sp\circ{dollar} N, 81{dollar}\sp\circ{dollar} W) Ontario, Canada. The MF radar uses the spaced antenna method by means of partial reflections to determine the horizontal winds. The VHF radar determines the horizontal wind velocity by means of radio reflections from meteor trails.;The major studies in this thesis include the following: (1) development of a numerical model to simulate the spaced antenna method, (2) validation of both radars, (3) studies of the spatial and temporal characteristics of tidal and mean motions over London with the MF radar, (4) studies of the spatial and temporal characteristics of the quasi 2-day wave over London with the MF radar, (5) comparison with other similar mid-latitude ground-based radars, (6) tidal/gravity wave interactions, and (7) intercomparison between MF and meteor VHF radar measurements.;Significant findings include the following: (1) The numerical model simulation results show that the full correlation analysis is consistent and a reliable tool for measurements of atmospheric motions. (2) Strong observational evidence of tidal/gravity wave interactions is found over London using the MF radar system. Our observations show significant correlation between gravity waves and tides (diurnal) at certain times of the year, and the nature of the correlation is intermittent and varies with time of year. We also propose a simple model which is found to be consistent with the major features of the observed data. (3) Our tidal studies show good and consistent agreement with other nearby studies and numerical models but with some notable exceptions. These exceptions are probably due to local effects like gravity wave interactions. (4) The periods of the quasi 2-day wave determined from our study, both at the London and Saskatoon sites, are found to be smaller (46-47 h) than the 51-52 h period generally suggested by other northern hemisphere results. Our observations show significant correlation between the London and Saskatoon sites on the 2-day wave during time periods of strong 2-day wave activity. The results suggest that the 2-day wave is a westward propagating wave of zonal wavenumber 3, although a possible connection with the zonal wavenumber 5 is also suggested at certain times. (5) Simultaneous comparison of winds and tides by MF and meteor VHF radars shows very good overall agreement between the two techniques. The important conclusion is "that in general and on the average and with relatively few exceptions the technique of MF spaced antenna drift measurements approximately reflect the real motions of the neutral air in he 85-94 km region, and therefore is a valuable tool in middle atmospheric research, at least for periods of greater than a few hours.
Recommended Citation
Thayaparan, Thayananthan, "Large And Medium-scale Dynamics In The Mesosphere And Lower Thermosphere Measured By Mf And Meteor Vhf Radars" (1996). Digitized Theses. 2627.
https://ir.lib.uwo.ca/digitizedtheses/2627