Southern Ocean circulation and frontal dynamics from Cryosat-2 a long-track radar altimetry

The Southern Ocean is a climatically important region, and its large-scale circulation in uences climate and climate change globally. Through the uptake of carbon and heat from the atmosphere, and through its in uence on the Antarctic Ice Sheet, the Southern Ocean circulation plays a pivotal role in regulating the global climate system, and impacts global mean sea level rise. This thesis uses Dynamic Ocean Topography (DOT) to investigate the largescale circulation and dynamics of the Southern Ocean and the Antarctic Circumpolar Current (ACC). DOT is the di�erence between the sea surface height and the Earth's geoid, both of which can be measured remotely using Earthorbiting satellites. A novel along-track DOT dataset is calculated and presented, by applying a direct along-track DOT calculation to radar altimetry measurements from Cryosat-2, thus exploiting its increased spatial coverage of the Southern Ocean in combination with the high resolution measurements inherent in the alongtrack data. The use of di�erent geoid models in this calculation is also investigated. The new along-track DOT dataset is then used to investigate inter-annual and seasonal variability in the DOT and currents of the Southern Ocean, revealing relationships with the large-scale climate modes of the El Ni~no Southern Oscillation and the Southern Annular Mode. The physical drivers behind these relations are shown to be linked to variability in wind forcing and the timevariable ocean mass signal. Bathymetry is also investigated as an important factor in setting the path of the ACC. The frontal structure of the ACC is analysed by applying two distinct frontal detection methods to the novel along-track DOT, and comparing inter-annual variability of frontal positions obtained through the two methods. Signi�cant inter-annual variability is observed in regions unconstrained by bathymetry, while frontal locations remain �xed in regions of constrained bathymetry such as ridges or plateaus, where the fronts converge.

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