Reanalysis of the Iceland-Faroe inflow

Bogi Hansen, Karin Margretha H. Larsen,Hjálmar Hátún and Svein Østerhus

NACLIM CT2, Hamburg, January 2015

Iceland-Faroe inflow

Old methodin situ CTD and ADCP (Hansen et al, 2003)

New method Combining Altimetry with CTD and ADCP

)(ˆ)(ˆ tuUtU kkk

Isoline(combined thermo and halo)

CTD stations

Altimetry points

ADCPs

Velocity profile

Average surface velocities

Geostrophy

Altimetry

ADCP

The depth of the 4°C isotherm

• Temperature field is linked to the velocity field (Hátún et al, 2004)

• EOF analysis of the altimetry SLA– Modes 1 and 2 explain 95% of the variability

• Tried regression of observed isotherm depth on various combinations of surface velocities and PC1 and PC2– Between 42 and 65% of variability explained by Uk

+ PC1

Calculating transports

),()(ˆ),( tztUtzU kk

7

2

500

0

)(),()(k z

kkTot zWtzUtQ

),0(/),(),( tutzutz ADCPADCP

)(),( ztz

)500()0(

)500()()(

AvgAvg

AvgAvgg ugug

ugzugz

)(zWk

Total transport: Konstant (to bottom or 500m)

AW transport: To bottom or average isoline

AW transport: To bottom or simulated isoline),( tzWk

AW transport 1993 - 2013

Average transport: 3.9 Sv

12 week avg

1 week avg

Simulating the temperature distribution

),,(365/),(2cos),(),(),,( Re msMaxmAmpAvm tikTikDtikTikTtikT

Tres: variance mainly associated with thermocline movement

Tres simulated by multiple regression on:

• AW temperature and 4°C isotherm depth (N04 – N11)

• AW temperature and altimetry principal component (N02 – N03)

Explained var.Using observed AW tmp and isotherm depth

Using simulated AW tmp and isotherm depth

Heat transport (relative to 0°C)

6

2

500

0

)(),(),()(ˆ)(k z

kkkk zWtzTtztUtH

AW v

olum

e tr

ansp

ort (

Sv) 1 yr avg

3 yr r.avg

Increase in Relative Heat Transport ≥ 10%

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