The mean dynamic topography (MDT) of the ocean is closely related to the mean surface
circulation. The objective of this thesis is to produce estimates of the MDT for the North
Atlantic using newly available data from ocean and gravity observing systems, to evaluate
these new estimates and so improve our understanding of the circulation.
Oceanographic estimates of the MDT are based on the mean temperature and salinity
(TS) fields of the ocean. These are typically averages from sparse observations collected
over many decades. The ocean is a non-stationary system so it is more appropriate to define
the mean for shorter, specific periods. Whilst the Argo observing system has increased the
frequency and resolution of in situ oceanographic measurements, high frequency (eddy)
variability remains. A new technique is described for removing this variability using
satellite altimeter measurements of the sea surface height. A new TS mean is produced,
relating to the period from 2000 to 2007, and this is used to map a new oceanographic
estimate of the MDT using an ocean circulation model.
New geodetic estimates of the MDT are produced using geoid models that incorporate
gravity measurements from the ongoing GRACE and GOCE satellite missions. These
are compared with the new oceanographic estimate and validated against independent
observations such as drifter speeds. The geodetic method produces realistic estimates of
the mean surface circulation, thereby realizing the long time dream of oceanographers to
observe the ocean circulation from space. The new oceanographic estimates are not as
accurate, but the new TS mean contributes to improvements in the performance of ocean
models, a necessary step in understanding and predicting the oceans.
Coastal tide gauges can provide an accurate estimate of the alongshore tilt of the coastal
MDT and this has been used to evaluate the above estimates. Temporal variability of the tilt
along the coast of the South Atlantic Bight is used, with statistical methods and an ocean
circulation model, to identify the processes contributing to the tilt. A new opportunity to
use tide gauges as part of an observing system for the ocean circulation is discussed.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:NSHD.ca#10222/14866 |
| Date | 07 May 2012 |
| Creators | Higginson, Simon |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
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