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Ann. Geophys., 23, 1977-1986, 2005
www.ann-geophys.net/23/1977/2005/
© European Geosciences Union 2005
Vertical structure of extreme currents in the Faroe-Bank Channel
C. Carollo1, I. Astin2, and J. Graff3
1The University of Chicago, Dept of the Geophysical Sciences, Chicago, IL 60637, USA
2The University of Bath, Dept of Electronic and Electrical Engineering, Bath, BA2 7AY, UK
3British Maritime Technology Ltd., Teddington, Middlesex, TW14 8LZ, UK
Abstract. Extreme currents are studied with the aim of understanding their vertical and
spatial structures in the Faroe-Bank Channel. Acoustic Doppler Current
Profiler time series recorded in 3 deployments in this channel were
investigated. To understand the main features of extreme events, the
measurements were separated into their components through filtering and tidal
analysis before applying the extreme value theory to the surge component. The
Generalized Extreme Value (GEV) distribution and the Generalized Pareto
Distribution (GPD) were used to study the variation of surge extremes from
near-surface to deep waters. It was found that this component alone is not
able to explain the extremes measured in total currents, particularly below
500 m. Here the mean residual flow enhanced by tidal rectification was found
to be the component feature dominating extremes. Therefore, it must be taken
into consideration when applying the extreme value theory, not to
underestimate the return level for total currents. Return value speeds up to
250 cm s–1 for 50/250 years return period were found for deep waters,
where the flow is constrained by the topography at bearings near
300/330° It is also found that the UK Meteorological Office FOAM
model is unable to reproduce either the magnitude or the form for the
extremes, perhaps due to its coarse vertical and horizontal resolution, and
is thus not suitable to model extremes on a regional scale.
Keywords. Oceanography: Physical (Currents; General circulation;
General or miscellaneous)
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