Integrated Marine Informations System - IMIS
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The response of southern North Sea elevations to oceanographical and meteorological forcing
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| Trefwoord |
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| Author keywords |
sea levels; currents; air-sea interaction; meteorological data; geodesy; North Sea |
| Abstract |
Relationships between the daily mean sea levels, air pressure, wind, density and currents of the southern North Sea are examined, using data recorded during September and October 1973 as part of the Joint North Sea Data Acquisition Programme. The sea level fluctuations are highly coherent through space. Principal component analysis shows that 88% of the variance can be accounted for by changes in the overall level of the southern North Sea. Seven per cent of the variance can be accounted for by an east-west tilting of sea level. Variations of the overall level are negatively correlated with air pressure changes. Cross-spectral analysis shows that the response of Southend sea level (i) lags the inverted barometer effect by 14 h and (ii) depends on the frequency of air pressure forcing. A qualitative explanation for these results is given. Wind stress is the most important influence on the daily mean surface topography of the southern North Sea, causing slopes in excess of 80 cm (100 km)-1. The largest slopes due to bottom stress, Coriolis acceleration and advection are 59 cm (100 km)-1, 34 cm (100 km)-1 and 13 cm (100 km)-1 respectively. The contributions of the equilibrium tide, local acceleration density and air pressure are small. It is shown that the sea surface topography, computed for a quiet period of several days, may be used to define accurately an equipotential surface at the tide gauge sites. A procedure for the estimation of depth-mean currents from sea level, air pressure and wind data is described. Reasonable agreement is obtained between observed and estimated currents at one position in the southern North Sea. |
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