The retroflection of the Faroe Current into the Faroe-Shetland Channel

1. The retroflection of the Faroe Current into the Faroe-Shetland Channel Karin Margretha H. Larsen, Bogi Hansen and Hjálmar Hátún Reykjavík, ICES ASC 2013

2. Arctic Ocean Nordic Seas Greenland Reykjavík FAROES Iceland Greenland-Scotland Ridge Scot- land North Atlantic

3. Monitoring of inflow The Faroe Current north of the Faroes One branch is retroflected into the Faroe-Shetland Channel How far does it progress into the channel? Observations: Standard CTD sections ADCP moorings Altimetry (AVISO MSLA) N E S Z

4. ADCP Mooring sites NB – 164 months EB, EC – 14 months SA(36), SX(12), SB(122) - months ZA – 10 months N NB EB E SA SX SB S ZA Z

5. Along track altimetry at site EB(Hátún, Thesis 2004) Altimetry The retroflection has a seasonal variability and steadily flows across section E

6. AVISO gridded altimetry (MSLA) PC1 is negative during winter EOF analysis Mode1 (Prior to analysis: Area average removed) PC1: timeserie of Mode1 LOW HIGH

7. EOF analysis: PC1 Seasonal analysis: minimum in late January

8. LOW PC1 and velocity at 200m Along topography NB: R = -0.62 EB: R = -0.78 SX: R = -0.86 Across topography NB: R = -0.41 EB: No correlation SX: No correlation SA: R = -0.37 (5% level) SA: R = -0.44 (1% level) N MSLA – EOF Mode1 A low SSH over the Norwegian Sea strengthens along-topography flow at the slopes NB EB E SA SX S Z

9. Variability in the FSC How far does the current progress into the FSC? Longterm mooring site SB has weak correlation with PC1 Individual years: 1999/00 and 2007/08 are correlated with PC1 N The retroflected FC reaches section S in some years... ...but perhaps site SB is not at an optimal location E SX SB ? S ? Z

10. Interannual variability SB SB No mooring data

11. Mode1 and the NAO index NAO winter index and the PC1 winter average are negatively correlated

12. Ongoing work Atmospheric forcing • Can we estimate the fraction of the retroflected Faroe Current? • Calculate volume flux, by combining in situ measurements and altimetry (Berx et al, 2013) • Atmospheric forcing and how it affects the retroflection

13. The research leading to these results has received funding from the European Union 7th Framework Programme (FP7 2007-2013), under grant agreement n.308299 NACLIM www.naclim.eu