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