We studied the global climatology of mid- and low-latitude F region daytime neutral winds using extensive measurements by the Wind Imaging Interferometer (WINDII) instrument on board the Upper Atmosphere Research Satellite (UARS). Quiet-time winds are mostly poleward and westward during the day, and are generally 5-20 m/s smaller in the longitudinal sector closest to the magnetic pole, compared to longitudinally averaged winds. The pre-noon zonal winds are less westward with increasing solar flux, while the post-noon meridional winds are less poleward . Our quiet-time results are in good agreement with the NCAR ThermosphereIonosphere- Electrodynamics General Circulation Model (TIEGCM). We computed residual winds by subtracting quiet-time values calculated along the satellite orbit, which effectively removes average measurement bias. Using these residuals, we studied the average change in the winds under disturbed conditions. The zonal disturbance winds are mostly westward, increase with latitude, and have largest values in the late afternoon sector. In general, the meridional perturbation winds are equatorward, increase linearly with latitude, and decrease from morning to afternoon hours. The zonal and meridional perturbations increase roughly linearly with Kp. We developed empirical analytical models for the disturbance winds from 60° to the equator; these model winds are in poor agreement with results from the empirical Horizontal Wind Model. There are also important discrepancies between the average perturbations winds from WINDII and TIEGCM. We studied the average time-dependent development of disturbance winds during geomagnetic storms. The onset of a storm is characterized by equatorward surges, mostly in the morning sector, that reach the equator in about 2 h. These surges lessen 5-6 h after the onset of a storm, but subsequently increase, reaching their largest values about 15 h after the start of the storm before leveling off or diminishing. Following the end of typical storms, the disturbance winds decrease quickly but oscillate for at least one 8-9 h cycle. We developed time-dependent analytical models of the disturbance winds as a function of the polar cap index at key storm time lags. Our results are consistent with predictions from theoretical models. (146 pages)

One of the intriguing features of the F-region ionosphere are anomalous evening enhancements of the electron density over certain mid-latitude sites. The most prominent example of this enhancement is the Weddell Sea Anomaly. Although the evening anomalies have been known for several decades, their generation mechanisms are still under debate and their accurate modeling remains a challenge. In this dissertation, the role of thermospheric neutral winds in the generation of these anomalies is investigated. Thermospheric winds play an important role in the dynamics of the F-region ionosphere, and, as it will be shown, in the generation of the evening anomalies. However, to date, their reliable estimation remains a challenge. To mitigate this shortcoming, data assimilation models were employed. First, seasonal global maps of F-region peak parameters (NmF2 and hmF2) from COSMIC radio occultation measurements were assimilated into the Global Assimilation of Ionospheric Measurements Full Physics (GAIM-FP) model. The model estimates magnetic meridional winds at low and mid-latitudes. GAIM-FP estimated winds were shown to be in good agreement with independent ground-based wind observations. Next, in order to address the role of neutral wind components in the generation of anomalies, a separate, 3-D physics-based Thermosphere Wind Assimilation Model (TWAM) was developed. TWAM is based on an implicit Kalman filter technique, and combines GAIM-FP magnetic meridional wind data with the equation of motion of the neutral gas to provide the climatology of the thermospheric wind components. The neutral wind components estimated by TWAM were also found to be in close quantitative agreement with independent ground-based wind observations, and were shown to accurately reproduce NmF2 and hmF2 over the anomalies. To understand the physical mechanism behind the anomalies, the plasma production, loss, and transport processes were analyzed. It was found that, due to the action of the equatorward wind, the evening density maximum forms at altitudes where the recombination rate is relatively small. It was revealed that at this time and altitude, plasma loss due to transport also weakens. As a consequence, the relative role of solar production increases over the net loss process and the electron density enhancement occurs.

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.

Bibliography : p. 333-342. / xiii, 342 p. : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 1994?

Bibliography : p.221-227. / xxiii, 227 p. : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 1994

This thesis demonstrates that at low frequencies (periods longer than 2.5 days) local currents off the coast of Oregon are closely related to the wind. Wind and current observations made during August and September 1969 are described and compared to demonstrate that a relationship exists; the physics of the interaction is not understood. The data are described as functions of both time and frequency. Spectral analysis shows that wind and current were related at frequencies less than 0.017 cycles per hour and at the diurnal frequency; at other frequencies they are apparently not related. The wind and current were then filtered to suppress frequencies higher than 0.017 cycles per hour; they are shown as functions of time. Comparison of the time series reveals certain features of the relationship between wind and current. The current can be considered to be the sum of two parts: a "response" current, which is related directly to the wind, and a "residual" current which is also variable. The amplitude of the response depends on the amplitude of the wind and on the density profile of the water. The time lag between the wind and the response current was variable; on a few occasions the current led the wind. Both the response and the residual current were generally parallel to the bottom contours. The residual current seems to change during periods when the response current is interrupted, so that short current records are not indicative of the mean flow. / Graduation date: 1971

This dissertation discusses a linkage between the Southern Ocean (SO) winds and the global ocean circulation in the framework of a coarse-resolution global ocean general circulation model coupled to a sea-ice model. In addition to reexamination of the conventional linkage that begins with northward Ekman transport and extends to the North Atlantic (NA) overturning, the author investigates a new linkage that begins with the Southern Hemisphere (SH) sea-ice – ocean interaction perturbed by the anomalous SO winds and extends to the SH overturning, the response of the NA overturning, and the long-term baroclinic adjustment of the Antarctic Circumpolar Current (ACC). How the above two linkages will interact with each other in a warming world is also investigated. An interactive momentum flux forcing, allowing for the strength of momentum flux between atmosphere and sea ice to vary in response to the simulated sea-ice conditions, enhances wind-driven ice divergence to increase the fraction of leads and polynyas, which increases dense water formation, and thus intensifies convection. Within three experimental frameworks, this increased dense water consistently increases the Antarctic Bottom Water formation, which directly intensifies the SH overturning and indirectly weakens the NA overturning. As a result of the hemispheric change in overturning circulations, the meridional density gradient across the ACC appears to increase, ultimately increasing the baroclinic part of the ACC via an enhanced thermal wind shear. Subsequently, impacts of the poleward shifted and intensified SH subpolar westerly winds (SWWs) on the global ocean circulation are investigated in phases. When the SWWs are only shifted poleward, the effect of the anomalous winds is transmitted to the northern NA, decreasing both the NA overturning and the North Atlantic Deep Water (NADW) outflow. However, when the SWWs are shifted poleward and intensified, this effect is cut off by the intensified Deacon cell overturning, and is not transmitted to the northern NA, and instead increases the NADW outflow substantially. To sum up, with respect to the SO winds perturbed by the global warming, the SH overturning cell and the NADW outflow increase, leading to an increase in the volume transport of the ACC.

Thesis (M.Sc.)--Memorial University of Newfoundland, 2000. / Bibliography: leaves 160-165.

Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 23, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Thesis advisor: Dr. Anthony R. Lupo. Includes bibliographical references.

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