Thesis (M.Sc.)--York University, 2005. Graduate Programme in Earth and Space Science. / Typescript. Includes bibliographical references (leaves 145-152). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url%5Fver=Z39.88-2004&res%5Fdat=xri:pqdiss &rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:MR11915

In the middle and upper atmosphere, dynamics of scales from tens of meters to thousands of kilometers primary arise due to the influence of gravity waves propagating from lower altitudes. In order to understand the structure and variability of these regions of our planet's atmosphere, we must understand the propagation, influences, and dissipation of gravity waves. However, gravity waves and their influences are difficult to measure. Their largest and most observable effects occur in the remote mesosphere and lower thermosphere and the relevant spatial scales extend across many orders of magnitude. The EBEX group discovered a novel method to observe polar mesospheric clouds, which are a sensitive tracer of gravity waves and their associated dynamics. This discovery motivated the Polar Mesospheric Cloud Turbulence (PMC Turbo) experiment. Polar mesospheric clouds form an extremely thin but bright layer at roughly 80 kilometer altitude in which we can observe brightness fluctuations created by gravity wave dynamics and the resulting instabilities. PMC Turbo included seven pressure vessels, each of which contained an optical camera, hard drives, and computers that controlled the image capture, flight control, and communication with ground stations. The cameras captured spatial scales from gravity waves with wavelengths of roughly 10-100 kilometers, instability dynamics at scales from about 1-10 kilometers, and the fine structure at the inner scale of turbulence down to 20 meters. PMC Turbo flew at 38 kilometer altitude and remained afloat for nearly six days. During this time, it travelled from Esrange Space Center in Sweden to the Northwest Passage in Canada. Complementary data from other instruments provides additional atmospheric context to the PMC Turbo measurements. During flight, the PMC Turbo cameras captured images of polar mesospheric clouds tracing Kelvin-Helmholtz instabilities with a high signal-to-noise ratio. Kelvin-Helmholtz instabilities play major roles in energy dissipation and structure of geophysical fluids, and they have a close relationship with gravity waves. The PMC Turbo images include complicated interactions and secondary instabilities leading to turbulence. These dynamics provide insight into the atmospheric conditions and rate of energy dissipation in the mesosphere and lower thermosphere.

Langzeitmessungen des Windfeldes in der Mesopausenregion (~ 92km) an verschiedenen Stationen in den mittleren Breiten der Nordhemisphäre zeigen systematische zonale Variationen beim (zeitlich) gemittelten Zonal- und Meridionalwind und bei den Amplituden und Phasen der halbtägigen Gezeiten. Als eines der herausragenden Muster, die zonale Variationen in der unteren mittleren Atmosphäre anregen, wird der Einfluß der Geopotentialstörungen zur zonalen Wellenzahl 1 und 2, die mit dem winterlichen stratosphärischen Polarwirbel verbunden sind, auf das Windfeld in der oberen Mesosphäre / unteren Thermosphäre numerisch mit dem COMMA-Modell der mittleren Atmosphäre untersucht. Die Modellergebnisse zeigen eine gute Übereinstimmung der zonalen Variationen des mittleren Zonalwindes, die im Breitenbereich 52ÆN bis 56ÆN beobachtet werden und in der Größenordnung von 10 - 20 m/s liegen. Auch die halbtägigen Gezeitenamplituden und -phasen zeigen qualitative und quantitative Übereinstimmungen zwischen Beobachtungen und Modellergebnissen. / Long-term time series of wind field observations in the upper mesosphere / lower thermosphere region at different locations in the midlatitude region indicate longitudinal variability in the (time-) mean zonal and meridional wind and in the amplitudes and phases of the semidiurnal tide, too. Being one of the prominent patterns forcing zonal inhomogenities in the lower middle atmosphere, the influence of the zonal wavenumber 1 and wavenumber 2 disturbances connected with the winter Northern Hemisphere stratospheric polar vortex on the mesosphere- / lower thermosphere wind field is numerically investigated with the COMMA model. The model results show that the zonal variations through the stationary waves coincide with typical observed mean zonal wind differences between different stations along the midlatitude belt between 52ÆN and 56ÆN with values about 10- 20 m/s. Also, the amplitude and phase variations of the semidiurnal tide show qualitative and quantitative agreements between model results and observations.

Mesopause region horizontal winds have been measured over Collm during winter 2000/2001 to investigate the response of the mesosphere/lower thermosphere region to a major stratwarm. The stratospheric warming resulted in a reversal of both the zonal and meridional wind. In the zonal component, this reversal was due to a planetary oscillation with period 10 days, which was even more pronounced in the vertical gradients, so that the stratwarm effect on the mesopause was owing to the superposition of an intensifying planetary wave (PW) and a slow overall decrease of the zonal prevailing winds. An effect of the stratospheric warming on the semidiurnal tide is also visible, namely by a decrease of the tidal amplitudes and rapid phase shifts in the order of 2 – 3 hours to later values. / Um die Auswirkungen von raschen Stratosphärenerwärmungen (Stratwarm) auf das Windfeld der Mesopausenregion zu untersuchen, wurden Messdaten des Horizontalwindes über Collm in den Monaten Januar und Februar 2001 untersucht, in denen eine große Stratosphärenerwärmung auftrat. Der Stratwarm zeigte sich im Windfeld in einer Höhe durch einen Rückgang des zonalen Grundwindes, sowie durch besonders starken Nordwind. Im Zonalwind zeigte sich eine deutliche Welle mit 10-tägiger Periode, die vermutlich den Stratwarm auslöste. Das hatte zur Folge, dass das Windfeld der Mesopausenregion während Stratwarm durch eine planetare Welle, sowie einen überlagerten Rückgang des Vertikalwindgradienten zusammengesetzt war. Ein Effekt des Stratwarm auf die halbtägigen Gezeiten war ebenfalls zu erkennen; die Gezeitenamplituden sind während der Stratosphärenerwärmung reduziert und die Phase liegt in einem kurzen Zeitraum um 2 – 3 Stunden später.

Meteor radar observations of mesosphere/lower thermosphere (MLT) daily temperatures have been performed at Collm, Germany since August 2004. The data have been analyzed with respect to long-period oscillations at time scales of 2–30 days. The results reveal that oscillations with periods of up to 6 days are more frequently observed during summer, while those with longer periods have larger amplitudes during winter. The oscillations may be considered as the signature of planetary waves. The results are compared with analyses from radar wind measurements. Moreover, the temperature oscillations show considerable year-to-year variability. In particular, amplitudes of the quasi 5-day oscillation have increased during the last decade, and the quasi 10-day oscillations are larger if the equatorial stratospheric winds are eastward.

This thesis presents observations of the 2-day planetary wave in the stratosphere, mesosphere and lower thermosphere. These observations were made using two ground-based meteor radars at polar latitudes and the satellite-borne microwave limb sounder (MLS) on the NASA Aura satellite. There have been relatively few observations of the 2-day wave at polar latitudes made using ground-based radars. This is particularly so in the Antarctic. Measurements of summertime and wintertime polar 2-day waves in the mesosphere and lower thermosphere (MLT) region were made using identical meteor radars at the conjugate geographical latitudes of Rothera (68!S, 68!W) in the Antarctic and Esrange (68!N, 21!E) in Arctic Sweden. This allows accurate quantification of the differences in the nature and seasonal variability of the 2day wave between the two polar regions. A clear seasonal variability is evident with the maximum amplitudes occurring during the summer months in both hemispheres. However, significant differences are found in the behaviour of the summertime wave between the two polar regions. In particular, wave activity is shorter lived but of larger amplitude in the Antarctic. These differences are suggested to be partly due to the different background winds of the two polar regions and possible differences in the component zonal wavenumbers in the northern and southern hemispheres. These radar studies have excellent spatial, height and time resolution but cannot resolve the component zonal wavenumbers of the 2-day wave. Therefore, Earth Observing System (EOS) Aura Microwave Limb Sounder (MLS) measurements of atmospheric temperature were used to investigate the climatology and interhemispheric differences of the different zonal wavenumbers (westward propagating zonal wavenumbers 2, 3 and 4) that compose the 2-day wave “complex”. This study demonstrates that the wave is dominated by different wavenumbers in the northern and southern hemisphere and that some of the interhemispheric differences observed in ground-based studies can be explained by the seasonal variability of these different zonal wavenumbers. These satellite studies led to participation in a multi-technique international collaboration to study the short-term variability of the summertime 2-day wave. Observations made in the northern hemisphere at mid-latitudes revealed that there are typically three peaks of enhanced 2-day wave amplitude during the summer, probably originating from a combination of baroclinic instability and critical wind speed.

A three-field photometer has been employed at the University of Adelaide's Buckland Park field site to collect optical observations of the 557.7nm OI and 730nm OH airglow emissions. Data have been collected on an almost continuous basis since May 1995 through to May 2000, with observations made whenever the moon was not up. Techniques and analysis procedures have been developed which allow routine extraction of the parameters of gravity waves observed each night. A cross-spectral analysis was performed on processed data from the photometer to identify short period (less than 3 hours) wave activity on nights where the impact of clouds on the data was minimal. The resulting wave parameters are analysed for seasonal variability and used to build up a climatology of wave parameters over the 5 years of observation. No consistent seasonal variation was observed, although there was a strong eastward perference to the wave's propagation direction. Implications of this finding are discussed. A co-located MF radar has been operating in spaced antenna mode providing wind data concurrent with the optical observations for most of the acquisition period. When available the wind data allowed calculation of the intrinsic parameters for waves identified in the optical data. The seasonal variablility of these parameters was investigated. An evaluation of energy and momentum fluxes estimated using the method of Swenson et al (1998b) was carried out. Approximations made in this method were found to be inappropriate for the waves detected by the photometer, and a refined procedure was therefore developed. This gave more realistic results, although large number of physically unreasonable momentum flux measurements were reported. Possible reasons for these were explored, and the need for further investigations emphasised. The five year dataset also allowed investigation of the long-term behaviour of the airglow. Both the intensity and variance were analysed using the Lomb-Scargle method across the complete dataset to identify the dominant periods present. Following similar treatment, the MF spaced antenna winds were compared with the optical results; this utilised a complex spectrum extension to the basic Lomb algorithm. Seasonally related periodicities of two years, one year, one half of a year and one third of a year were observed in the optical data, along with a possible signature of a five and a half year period potentially linked to the eleven year solar cycle. The radar data did not have stong signatures of the one third of a year periodicity although the presence of an five and a half year periodicity could not be ruled out. Gravity wave activity, as measured by the optical intensity variance, reached a maximum during autumn with a secondary maximum occurring in spring. The annual variability of the wave spectrum detected by the photometer was also studied which showed a falloff in the wave energy at short periods (less than thirty minutes) during autumn and spring. This suggested that the enhanced wave activity at these times consisted mainly of waves with periods greater than thirty minutes. / Thesis (Ph.D.)--Department of Physics and Mathematical Physics, 2000.

A three-field photometer has been employed at the University of Adelaide's Buckland Park field site to collect optical observations of the 557.7nm OI and 730nm OH airglow emissions. Data have been collected on an almost continuous basis since May 1995 through to May 2000, with observations made whenever the moon was not up. Techniques and analysis procedures have been developed which allow routine extraction of the parameters of gravity waves observed each night. A cross-spectral analysis was performed on processed data from the photometer to identify short period (less than 3 hours) wave activity on nights where the impact of clouds on the data was minimal. The resulting wave parameters are analysed for seasonal variability and used to build up a climatology of wave parameters over the 5 years of observation. No consistent seasonal variation was observed, although there was a strong eastward perference to the wave's propagation direction. Implications of this finding are discussed. A co-located MF radar has been operating in spaced antenna mode providing wind data concurrent with the optical observations for most of the acquisition period. When available the wind data allowed calculation of the intrinsic parameters for waves identified in the optical data. The seasonal variablility of these parameters was investigated. An evaluation of energy and momentum fluxes estimated using the method of Swenson et al (1998b) was carried out. Approximations made in this method were found to be inappropriate for the waves detected by the photometer, and a refined procedure was therefore developed. This gave more realistic results, although large number of physically unreasonable momentum flux measurements were reported. Possible reasons for these were explored, and the need for further investigations emphasised. The five year dataset also allowed investigation of the long-term behaviour of the airglow. Both the intensity and variance were analysed using the Lomb-Scargle method across the complete dataset to identify the dominant periods present. Following similar treatment, the MF spaced antenna winds were compared with the optical results; this utilised a complex spectrum extension to the basic Lomb algorithm. Seasonally related periodicities of two years, one year, one half of a year and one third of a year were observed in the optical data, along with a possible signature of a five and a half year period potentially linked to the eleven year solar cycle. The radar data did not have stong signatures of the one third of a year periodicity although the presence of an five and a half year periodicity could not be ruled out. Gravity wave activity, as measured by the optical intensity variance, reached a maximum during autumn with a secondary maximum occurring in spring. The annual variability of the wave spectrum detected by the photometer was also studied which showed a falloff in the wave energy at short periods (less than thirty minutes) during autumn and spring. This suggested that the enhanced wave activity at these times consisted mainly of waves with periods greater than thirty minutes. / Thesis (Ph.D.)--Department of Physics and Mathematical Physics, 2000.

Thesis (Ph. D.)--University of Adelaide, Mawson Institute for Antarctic Research, 1990. / Copies of author's previously published articles inserted. Includes bibliographical references (leaves 219-226).

The dynamics of the atmospheric meteor region have been studied using the data obtained with - - the Grahamstown (33°16'S, 26<>:30'E) meteor radar between the years 1987 and 1993 inclusive. Harmonic analysis and the maximum entropy method (MEM) , were used for the spectral characterization ofthe wind above Grahamstown. The prevailing wind, tidal (periods 12- and 24- h) and other (periods 8- and 6-h) oscillations were extracted from the data using the guidelines agreed upon by the A TMAP community. Above Grahamstown the zonal and meridional prevailing winds were found to be predominantly eastward and equatorward respectively. Tidal amplitudes are comparable to the magnitude of the prevailing wind vector, with the diurnal tide being stronger than the semidiurnal tide. The phase differences between ,the zonal and meridional components of the semidiurnal and diurnal tides are - 2 hand - 5 h respectively, which is in reasonable agreement with the corresponding expected values of3 hand 6 h. The tidal wind vectors are on average elliptically polarized with anticlockwise rotation. Longitudinal and day-to-day tidal variations were studied. From the longitudinal study, the semidiurnal tide was found to be dominated by migrating modes, while the diurnal tidal behaviour suggests the presence of nonmigrating modes with zonal wavenumber s = 4. Tides were found to be variable from day to day with little apparent correlation between the zonal and meridional components of the respective tides.