the retroflection of the faroe current into the faroe-shetland channel karin margretha h. larsen,...

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

Karin Margretha H. Larsen,Bogi Hansen and Hjálmar Hátún

Reykjavík, ICES ASC 2013

Iceland

Scot- land

NordicSeas

ArcticOcean

Greenland

North Atlantic

Greenland-Scotland Ridge

ReykjavíkFAROES

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?

N

E

S

Z

Observations:

Standard CTD sections

ADCP moorings

Altimetry (AVISO MSLA)

ADCP Mooring sites

NB – 164 months

EB, EC – 14 months

SA(36), SX(12), SB(122) - months

ZA – 10 months

N

E

S

Z

EB

SXSASB

ZA

NB

Along track altimetry at site EB (Hátún, Thesis 2004)

Altimetry

The retroflection has a seasonal variability and steadily flows across section E

AVISO gridded altimetry (MSLA)

EOF analysis Mode1 (Prior to analysis:Area average removed)

PC1: timeserie of Mode1

PC1 is negative during winter

LOW

HIGH

EOF analysis: PC1

Seasonal analysis: minimum in late January

PC1 and velocity at 200m

Along topographyNB: R = -0.62EB: R = -0.78SX: R = -0.86

Across topographyNB: R = -0.41EB: No correlationSX: No correlationSA: R = -0.37 (5% level)

SA: R = -0.44 (1% level)

N

E

S

Z

NB

EB

SXSA

MSLA – EOF Mode1A low SSH over the Norwegian Sea strengthens along-topography flow at the slopes

LOW

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

E

S

Z

??

The retroflected FC reaches section S in some years...

...but perhaps site SB is not at an optimal location

SXSB

Interannual variability

SB

No mooring

data

SB

Mode1 and the NAO index

NAO winter index and the PC1 winter average are negatively correlated

Ongoing work

• 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

Atmospheric forcing

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