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Wind driven seasonal variations in the transport of NAW through the Faroe-Shetland Channel

Wind driven seasonal variations in the transport of NAW through the Faroe-Shetland Channel. Toby Sherwin Scottish Association for Marine Science, Oban Acknowledgements: Bill Turrell, Sarah Hughes, Bee Berx (Marine Scotland), Bogi Hansen (FFL), Svein Ø sterhus (UiB). also acknowledge:

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Wind driven seasonal variations in the transport of NAW through the Faroe-Shetland Channel

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  1. Wind driven seasonal variations in the transport of NAW through the Faroe-Shetland Channel Toby Sherwin Scottish Association for Marine Science, Oban Acknowledgements: Bill Turrell, Sarah Hughes, Bee Berx (Marine Scotland), Bogi Hansen (FFL), Svein Østerhus (UiB) • also acknowledge: • European Commission (MOEN – ASOF EU-E, Framework V) based on: Sherwin, T.J., Hughes, S.L., Turrell, W.R., Hansen, B., Østerhus, S., 2008. Wind-driven monthly variations in transport and the flow field in the Faroe–Shetland Channel, Polar Research 27 (1), 7-22. Sherwin, T.J., Williams, M.O., Turrell, W.R., Hughes, S.L., Miller, P.I., 2006. A description and analysis of mesoscale variability in the Faroe-Shetland Channel. JGR 111, ISI:000235995000002 (C3).

  2. NSDW + MNAW NAW Bathymetry of the Faroe – Shetland Channel

  3. THE PROBLEM OF MESOSCALE VARIABILITY

  4. B C D E Velocities and transport in the NAW at 4 ADCPs Sv Hughes et al., (2006) cm/s From different methodologies: Hughes et al., (2006) mean NAW transport = 4.0 Sv (trend ~ -0.1 Sv per annum) Sherwin et al,. (2008) mean NAW transport = 3.5 Sv±0.1 Sv (2.1 Sv barotropic, 1.4 Sv baroclinic)

  5. 0423 h 19 May 1999

  6. 23 233 359 397 209 Surface drifter and ADCP EKE (cm2 /s2)

  7. SEASONAL VARIATION IN THE MEAN FLOW

  8. 2.0 Sv 5.3 Sv 3.8 Sv Mean surface drifter velocities (6000 days of data)

  9. Monthly mean velocities in the upper 500 m

  10. Correlation between monthly mean transport in the upper 500 and SW wind stress from NCAR/NCEP 4.1 Sv 2.3 Sv

  11. BAROCLINIC / BAROTROPIC BREAKDOWN

  12. 15 June 1997, Qgeo = 0.33 Sv 12 September 1999, Qgeo = 1.7 Sv MNAW NAW Examples of strong and weak geostrophic transport (from CTD sections)

  13. Mean ADCP Geostrophic Mode 1 Mean and mode 1 transports across the FSC

  14. HOW THOR IS ADDRESSING BOTH PROBLEMS (mesoscale variability and the shelf edge)

  15. In THOR we add 2 extra ADCPs

  16. Trawl proof frame for shallow mooring

  17. SUMMARY • Contrary to earlier shorter term analysis there does appear to be a seasonal variation in the transport of NAW of ~ 1.8 Sv (± 50%) • Identified some difficulties that limit the accuracy of absolute mean transport • Large mesoscale variability makes it difficult to determine means and trends with this configuration • After 15 years of observation it is difficult to argue for a relocation of the moorings

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