Master Thesis by Jon Saabye – Niels Bohr Institute - University of Copenhagen

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Master Thesis by Jon Saabye

Inter-Annual Sea level Variations Forced by Wind Stress in the Subtropical North Arlantic

(this talk will be in Danish)

This master thesis is the result of an investigation in how wind stress influence the variability of the Sea Surface Height (SSH) in the north Atlantic, in the period 1993-2008. A Reduced Gravity Model (RGM) has been used to compare the variability of the pycnocline to the SSH measured by the satellites TOPEX/Poseidon and Jason-1.

The RGM is a two layer model, with a motionless lower layer, also referred to as an 1½-layer model. The model neglects thermodynamics and bathymetry effects, but includes real coast lines. The RGM is discretized on an Arakawa C-grid and solved with a standard leap-frog scheme. Empirical Orthogonal Functions (EOFs) have been used to decompose the satellite altimetry, RGM output, and the curl of the wind stress into statistically independent spatial and temporal patterns.

After using a box-car filter, the first EOF from the satellite altimetry decribes 50.3% of the variability, with a dominating signal in the Gulf Stream system and in the tropics. The principal component shows a decrease from 1994-2004. This was found to be related to the first baroclinic mode and the adjustment time of the Rossby waves in the RGM. The second EOF describes 17.1% of the variability, with a dominating signal in the Sargasso Sea. The principal component had a period of 3-5 years, which was in good agreement with the wind stress curl

Supervisors: Niels Kristian Højerslev, NBI, University of Copenhagen
Torben Schmith and Ole Krarup Leth, Danish Meteorological Institute