The identification and tracking of Agulhas rings using satellite altimetry

• Main Author: Taunton-Clark, John
• Format: Dissertation
• Language: English
• Published: University of Cape Town 2016
• Subjects: Oceanography
• Online Access: http://hdl.handle.net/11427/21515

Includes bibliographical references. === The methods of analysing, interpreting and computing surf ace geostrophic currents from GEOSAT altimeter data are explained. These methods were implemented in an examination of GEOSAT altimeter data for the period 12 July 1988 to 13 May 1989 with application to the identification and tracking of Agulhas rings in the southeast Atlantic Ocean. A population of as many circulation features of as five anticyclonic (and cyclonic) annular form consistent with that reported for Agulhas rings was identified from the altimeter data. The positive identification of the same feature in subsequent repeat cycles was, however, difficult. The Verna ring was identified as it travelled approximately along the ground track of GEOSAT pass A 158. Its horizontal (approximately 200 km diameter) and vertical (>30 cm sea surface elevation) dimensions confirmed its identity as an Agulhas ring. The translation speed of the Verna ring along pass A 158 was determined as 6.8 cm·s⁻¹ consistent with the speeds reported in the literature. Surface geostrophic speeds calculated from the altimeter-derived sea surface slopes showed maximum anticyclonic speeds of nearly 40 cm·s⁻¹ toward the SW at the northern rim and 25 cm·s-1 toward the NE at the southern edge of the ring.