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Title: Radar studies of the dynamics of the mesosphere and lower thermosphere
Author: Younger, Peter Thomas
ISNI:       0000 0001 3575 8864
Awarding Body: University of Bath
Current Institution: University of Bath
Date of Award: 2004
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Meteor radars are powerful tools for the study of the atmosphere at heights between -80-100 lan. These heights span the boundary between the mesosphere and the lower thermosphere (MLT) and include the temperature rp.inimum of the mesopause - the coldest naturally occurring place on Earth. This thesis describes studies made using two modem VHF meteor radars. The first was installed at Esrange (68°N, 21°E) in Arctic Sweden in October 1999. The second was deployed on Ascension Island (80 S, 14°W) in the equatorial Atlantic in May 2001. The work is in three parts. The first part is a study of the behaviour of the 8-hour tide at Arctic latitudes undertaken with the Esrange meteor radar. The tide is found to be a persistent feature of the Arctic MLT region and, at times, its amplitude can exceed that of the 24-hour tide. This study investigates the possible excitation mechanisms of this tide - proposals for which have included either direct thermal excitation or non-linear coupling between the 12- and 24-hour tides. The results suggest that, at least some ofthe time, non-linear interactions may contribute to the excitation ofthe tide. The second part uses one year of data from the Ascension Island radar to construct a simple climatology of the mean winds and 12- and 24-hour tides in the equatorial region. The mean winds reveal the clear signature ofthe planetary-scale Dobson-Brewer circulation. Comparisons with simultaneous observations made at higher latitudes suggest that the circulation may contain significant longitudinal structure. The tides are found to be a major part of the MLT-region motion field over Ascension Island. Comparisons with the NCAR HAO Global Scale Wave Model and equatorial observations of tides made elsewhere reveal a number of significant differences and points to the potential importance of non-migrating tides. The final part investigates the planetary-wave field in the MLT region over Ascension Island. A rich and varied field ofplanetary waves is evident. Detailed studies address the quasi-two-day wave, ultra-fast Kelvin waves with periods near three days and the 16day wave. The seasonal behaviour and variability of each type of wave is delineated. Observations of ultra-fast Kelvin waves suggest that the effects of inertia-gravity waves must be considered in the analysis ofsuch waves.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available