Two possible ionospheric electric currents for Pi2 micropulsations are investigated and tested against data collected from a meridian chain of stations in Saskatewan. The electric coupling between the ionosphere and the magnetosphere under disturbed magnetospheric conditions is believed to be the cause of the Pi2 generation and propagation. The LC circuit analogy is first used to model this interaction, the source of energy lying in the magnetospheric equatorial plane. Secondly, the possibility of an ionospheric electric impulse imparted to a field-aligned current under the conditions of brightening of aurora is considered. It is found experimentally that the Pi2 originates possibly from these two source regions: the characteristics of a resonant LC oscillation expanding symmetrically to the west and to the east of the magnetospheric potential source are observed, as well a strong toroidal field existing and possibly originating in the ionosphere. It is suggested that optical data in conjunction with auroral radar echo and satellite data be necessary to confirm a future mathematical development of these possible Pi2 generation and propagation models. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Spectral characteristics of sub-surface current and temperature records spanning 310-533 days from me Strait of Georgia near Sturgeon Bank are examined. Of particular interest are low-frequency fluctuations having, a characteristic period of 30 days. Typically, the energy of the low-frequency and tidal currents are equal at 50m (each about 40% of the total), and 10% and 10%, respectively, at 200m. Low-frequency currents are observed to be baroclinic and posses a lateral length scale less than 10km. Their generation mechanisms are not identified. The low-frequency fluctuations in sea-level and current have poor-to-fair coherence, while those in air-pressure and current have poor coherence. Low-frequency fluctuations in wind and current have fair coherence at the eastern mooring, and poor coherence at the remaining two moorings. Fluctuations in water temperature have a characteristic period of 300 days. Water temperatures at different locations generally have poor coherence except at the lowest frequencies where they are fair-to-good. Water temperature and current at the same location have poor coherence. Tidal currents are found to be ellipses, with the largest constituents being M² and K¹. The magnitude, shape .and orientation of the tidal current ellipses are time-dependent. Internal tides are suggested as an explanation. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Time variations of the Pacific equatorial undercurrent at 150° west longitude are described, based upon observations from the CSS Parizeau during January-February 1979. Typical velocity maxima were 80 cm s⁻¹ in the eastward direction and 60 cm s⁻¹ in the northward direction near the core depth at 150 metres. Associated standard errors were 15 cm s⁻¹ due to uncertainty in probe motion and 5 cm s⁻¹ due to inherent current meter noise. Scalar field analysis suggests that the mean zonal current flow in the equatorial undercurrent is modulated by Rossby waves with periods of 30 days. In the surface layer, waves with periods of approximately 17 days were detected. A detailed description of the current profiler used during the experiment is included in the Appendix. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Several theoretical models of the wave-induced current circulation in the vicinity of a breakwater extending from shore are presented. The models,which are patterned after a local field site, include several numerical models which take into account variable sea-floor topography and which compare the effects of linear and non-linear bottom friction as well as an analytical model characterized by semi-infinite beaches and uniform sea-floor topography. In general (for a given angle of wave incidence) the circulation patterns show two counter-rotating cells driven by wave-induced longshore currents which flow along both the breakwater and natural beaches toward their common intersection corner, with an offshore return flow in the form of a rip current. The qualitative features of the models are consistent with observations of sediment transport taken at the study site. Differences in the linear and non-linear bottom friction models do not become apparent until an off-shore trench parallel to the breakwater is introduced to the sea-floor topography. The non-linear model shows a deflection of the off-shore return flow into the trench in agreement with preliminary analysis based on a one-dimensional model. The linear results, however, differ considerably from those of the non-linear model and are difficult to interpret, showing an inordinate increase in transport over the trench. During the development of the analytical model difficulties were encountered due to the complexities of the analysis which necessitated that part of the solution be solved numerically. The results, while showing the same general features as the numerical models, exhibit a much more strongly divergent off-shore return flow. This difference, while unresolved, appears to be one of scale rather than of form. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The Indonesian Throughflow (ITF) is the only low latitude connector between the Pacific and Indian Oceans affecting upper ocean stratification and regional climate. Here we focus on the Indian Ocean side of this connection, first identifying changes within the primary throughflow pathway within the Indonesian Seas, then following the throughflow as it moves within the eastern tropical Indian Ocean. Moored velocity measurements and an ENSO varying temperature profile developed from all available observations within the Makassar Strait are used to determine the southward heat flux anomaly (HFa) within this primary pathway of the ITF. Variability in the velocity profile is more important than that of the temperature profile for determining changes in the total heat flux with the former accounting for 72% of the variance in HFa and the latter 28%. As the upper layer (0-300 m) is the site of the largest volume transports and also the largest transport variability, upper layer HFa is far more dominant than the lower (320-740 m) in influencing the total depth integrated HFa. Upper ocean heat content anomaly (0-300 m; HCa) in the eastern tropical Indian Ocean calculated from gridded Argo datasets is well correlated with Makassar HFa at interannual timescales (r = 0.8). The lag between the two is 2.5 years, indicating that this is consistent with an advective signal. From the Indo-Australian basin ITF waters flow either into the South Equatorial Current (SEC) to the west or the Leeuwin Current (LC) to the south. Gridded Argo data is used to track upper ocean heat content changes from the immediate outflow area into these two currents. The heat content anomaly timeseries in the region closest to the Indonesian Seas is well correlated with that at the easternmost section of the SEC with r = 0.8 at a 5 month lag. A notable exception occurs during 2011 when a positive heat content anomaly in the ITF outflow region is not later reflected in the SEC region, but rather expressed as an HCa increase the LC region. When compared to a previous HCa increase in the ITF outflow region during 2009, GODAS reanalysis shows that the velocity within the SEC was stronger eastward and the LC stronger southward during 2011. The Ningaloo Niño of 2011 was characterized by a low pressure anomaly off the west Australian Coast, which induced anomalous cyclonic circulation seen in NCEP/NCAR reanalysis winds at 1000 HPa. The positive zonal wind anomalies over the SEC and the reduction of southerly winds over the LC influenced these changes in current velocity. During the Ningaloo Niño of 2000 a similar pattern in atmospheric and oceanic circulation was identified. These results confirm the importance of the Ningaloo Niño in influencing the pathways of the ITF out of the Indo-Australian basin. Additionally, over the Argo time period, volume transport via the LC and SEC pathways appears anti-correlated, with increases in SEC outflow coupled with decreases in LC outflow. As the SEC is the major pathway for the ITF within the Indian Ocean, we examine the propagation of these low salinity waters within the SEC thermocline. Using gridded Argo data, we examine the salinity along the 24σ surface as a proxy for ITF propagation, and the depth of the 20°C isotherm (d20) to determine how changes in the thermocline depth may affect the flow. The d20 was correlated with the salinity (r=-0.5) in the region of the Seychelles Chagos Thermocline Ridge (SCTR), indicating that this region of upwelling, and the geostrophic currents that form around it, play a role in the westward propagation of the ITF. When examining the seasonal cycle, the effect of the SCTR is apparent as low salinity contours within the western portion of the basin show the furthest westward propagation during austral winter, when the SCTR is strong and most longitudinally expansive. On interannual timescales two years, 2010/11 and 2016/17, show anomalously high salinity in the SEC thermocline indicative of a reduction of ITF westward propagation. During late 2010 and 2016 anomalously strong upwelling regions are present at about 80°E and 10°S, out of the normal season for strong upwelling at this location. GODAS reanalysis velocity at 105 m shows cyclonic circulation developed around these upwelling centers, disrupting the normal zonal pathway of the SEC and reducing the amount of ITF able to propagate into the central Indian. As seen in the 34.8 salinity contour, both 2011 and 2017 show a reduction of 20 degrees of longitude of ITF westward propagation when compared to climatology. These upwelling regions were caused by both regional winds conducive to Ekman upwelling at that location, in addition to the absence of the annual westward propagating downwelling Rossby wave. This wave was absent during both late 2010 and 2016 due to positive zonal wind anomalies in the south east tropical Indian Ocean caused by a simultaneous occurrence of La Niña and a negative IOD.

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Thesis (M.C.E.)--University of Delaware, 2006. / Principal faculty advisors: Dominic M. Di Toro and James T. Kirby, Dept. of Civil & Environmental Engineering. Includes bibliographical references.