Dissertation (PhD)--University of Stellenbosch, 2008. / Bibliography. Also available via the Internet.

Thesis (M.S.)--Naval Postgraduate School, 1975. / Includes bibliographical references (leaves 78-79).

Thesis (M.S.)--U.S. Naval Postgraduate School, 1964.

Thesis (M.S. in Applied Science (Physical Oceanography))--Naval Postgraduate School, June 2005. / Thesis Advisor(s): Thomas H.C. Herbers. Includes bibliographical references (p. 45). Also available online.

A free-fall oceanographic instrument has been used to measure vertical microstructure scale gradients of horizontal velocity, temperature and electrical conductivity. The velocity gradients, or shears, were measured at scales between 3 and 40 cm by an airfoil shear probe whose specifications and calibration procedure are discussed. Data collected in the equatorial Atlantic in July 1974 indicated a consistent pattern of turbulence near the velocity core of the Atlantic Equatorial Undercurrent. (The velocity core is the region of maximum speed. ) The most intense turbulence was found above the velocity core of the undercurrent. Turbulence in the velocity core was weak and intermittently spaced. Below the core, near the base of the thermocline, moderately intense turbulence was found. The rate of viscous dissipation of turbulent energy has been estimated from the shear measurements, and typical values were 3x10 ⁻³ cm² sec ⁻³ above the velocity core. Spectra of the shears have been computed. At small wavelengths the measured spectral coefficients fall below the universal Kolmogoroff spectrum. This discrepancy between the two spectra is attributed to spatial averaging of velocity fluctuations by the shear probe. The estimates of viscous dissipation include a correction for this spatial averaging. An energy balance has been determined for the turbulent velocity fluctuations. Above and below the core the basic balance is local production of turbulent energy equals local dissipation, and this balance gives a vertical eddy viscosity of order 10 cm² sec ⁻¹ above the core. The equation of the energy balance of the average motion has been vertically integrated at the equator where meridional terms are assumed small. In the South Equatorial Current the rate of energy gain from the average zonal wind stress is balanced by the rate of energy loss to the zonal pressure gradient plus the rate of dissipation. In the undercurrent, above the core, the rate of energy gain from the zonal pressure gradient equals the rate of dissipation within the uncertainty of the measurements, and the advection term is small but not negligible. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Call number: LD2668 .T4 1939 L41 / Master of Science

This research describes the position, strength and variability of the mixing front along the East Shetland coast and the geostrophic current associated with the front. Between 2004 and 2010, new current meter measurements have been made at two mooring sites on the East Shetland shelf. By combining the current meter datasets with other surface temperature and salinity observations, such as surface underway data from the ferry MV “Norröna” and existing hydrographic datasets, this research provides new insights into the seasonal variability of the currents on the east Shetland shelf. The results show that in this region of the northern North Sea the balance of heating-stirring results in a tidal mixing front close to a (log10( h/u3)) of 3.4. Along the steeply sloping shelf to the east of Shetland a mixing front is found in water around 100m depth and results in significant geostrophic currents of up to 20 cm/sec between June and August each year. Monthly volume transports associated with broad scale wind forcing are estimated to be between -0.27 and -0.51 Sv during the well mixed periods (December to March). During the summer months (June, July and August) wind driven transport reduced to an average of -0.27 Sv, at the same time the persistent southerly flow associated with the geostrophic transport contributes an equivalent transport (-0.24 Sv). Taking the east Shetland shelf as a whole (coast to 1.5°E) the maximum volume transport is estimated to occur in Autumn (September to October) when density driven currents remain significant and wind speeds begin to increase. In the narrow region close to the coast, however, monthly mean volume transport is observed to be highest during the summer months as a result of the strong jet-like currents that flow along the density front.

No description available.

In this thesis we determine the electromagnetic fields of a current distribution located, in free space, above a perfectly conducting plane earth. Then we consider the inverse problem of determining the source distribution from the fields. Formulae are obtained for the volume integral (dipole moment) of the current density of a small current source in terms of the fields and known functions. If field data are measured (from lightning over sea water for example) the dipole moment of the current density producing the fields may be found. The validity of the small source approximation used in this work is also established. Finally, a method is developed for determining the average current at points on a vertical line current source, a common model for a lightning return stroke. We treat the source as a string of dipoles and apply a method of constrained inversion.

No description available.