Ocean eddies off southern Norway Ingerid Fossum Avslutningskonferanse MARE, Scandic Hotell Edderkoppen, Oslo, 12-13 oktober 2005
Main questions: Does MI-POM reproduce the circulation pattern in Skagerrak? Where do we find instability in Skagerrak? What kind of instability is it? Skagerrak Norway Lista Is there a connection between instability and anticyclonic eddies off Lista? Denmark
Motivation: An area of high biological production One of the most difficult and hazardous waters to navigate To give better predictions about where to expect extreme current velocities
Satellite image SST (contrast enhanced) Lista
Current from MI-POM Lista
Energy diagnostics: K t M + ( F F ϕ K + R ) = CM + C M ME + S KM ϕ + ( F + P) t = C ϕ ϕ M CE + S ϕ K t E + F K = C ϕ E C ME + S E K E
Potential vorticity analysis Charney-Stern criterion: A jet is baroclinically stable if the gradient of Ertel s PV does not vanish across the jet If the gradient does vanish it constitutes a necessary condition for baroclinic instability
Mean kinetic energy (K M ) B A October May B A
Eddykineticenergy(K E ) B A October May B A
Conversion of energy between K M and K E (C ME ) B A October May B A
Conversion of energy between Φ and K E ( Φ ) C E B A October May B A
Upstream of Lista (point marked A ) Energy components Conversion terms 15000 K M K E 0.3 0.2 C ME C E Φ J/m 2 10000 5000 0.1 0 0.1 W/m 2 0.2 0 0 100 200 300 Days 0 100 200 300 Days
Off the southern tip of Norway (point marked B ) Energy components Conversion terms 15000 K M K E 0.3 0.2 C ME C E Φ J/m 2 10000 5000 0.1 0 0.1 W/m 2 0.2 0 0 100 200 300 Days 0 100 200 300 Days
PV and 30 days mean current at 50 m 12 May 2001 B A 7 October 2001 B A
Current and salinity at 30 m 17 October 2001
Conclusions: MI-POM reproduces the circulation pattern in Skagerrak The NCC veers offshore east of Lista Barotropic and baroclinic instabilities are highly active east of Lista Only weak instability off Lista Seasonal variation of the instability Strong instability east of Lista anticyclonic eddies off Lista
Major implication: A new method is developed to forecast anticyclonic eddies off the southern tip of Norway
The end
Future work: Determine the cause of the anticyclonic eddies off Lista Determine why the NCC veers offshore east of Lista Calculate all the terms in the energy equations Study the effect of variation in fresh-water inflow Study the effect of changing wind conditions
Skagerrak topography Oksøy Hanstholm
Skagerrak salinity and current 04.11.2001 Norway Lista Denmark
Skagerrak Norway Lista Denmark