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Statistics of low frequency currents over the western Norwegian shelf and slope I: current meters

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Abstract

We examine records from current meters deployed over western Norwegian shelf and slope during the period of 1976 to present. Though many of the records are shorter than six months, when taken together they yield a coherent picture of the field. The mean flow is dominated by the Norwegian Atlantic Current (NwAC) near the shelfbreak, with surface velocities of order 60 cm/sec. The variance is surface-intensified and increases with water depth over the shelf, but is more homogeneous on the slope and just offshore. The variability is strongly seasonal over the shelf but much less so over the slope. Autocorrelations suggest short temporal (1–3 days) and spatial (10–20 km) scales, consistent with deformation-scale eddies. There is evidence for a long range (O|100|km) correlation at the shelfbreak, in the core of the NwAC; otherwise the variability is strongly localized.

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Notes

  1. We know however that topography exerts a strong influence on the time-varying currents here (Isachsen et al. 2003), and this may in turn affect the path of the mean flow.

  2. In the shallowest regions, only instruments in the upper half of the water column were used for the shallow statistics, to avoid overlap with the deep instruments.

  3. The projection was made onto the etopo5 topographic data set, smoothed to remove scales smaller than about 15 km. As such, the along-isobath direction will differ somewhat from reality, depending on the location.

  4. The PDF is normalized. To evaluate the actual strength of the currents, one must know the standard deviation, as shown in Fig. 6.

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Acknowledgments

The work was supported under a grant from the Norwegian Deep Water Program (NDP) by Norske Shell and by the Ormen Lange license by Norsk Hydro. Further support was provided by the NOCLIM program, funded by the Norwegian Research Foundation. The data were collected and archived under NDP, except for the Svinøy data, which were graciously provided by K.A. Orvik, University of Bergen. C. Mauritzen provided useful input on the local circulation and commentary from two anonymous reviewers helped improve the manuscript.

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  1. Norwegian Meteorological Institute, P.O. Box 43, Blindern, 0313, Oslo, Norway

    J. H. LaCasce

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  1. J. H. LaCasce
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Correspondence to J. H. LaCasce.

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LaCasce, J.H. Statistics of low frequency currents over the western Norwegian shelf and slope I: current meters. Ocean Dynamics 55, 213–221 (2005). https://doi.org/10.1007/s10236-005-0021-6

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  • DOI: https://doi.org/10.1007/s10236-005-0021-6

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