Department of Geophysics University of Bergen Spin-up; monthly forcing; daily forcing; relaxation T and/or S Topics; • Variability guided by observed changes (mainly) in the Atlantic; particularly the gyre variability • Inflow to the Nordic Seas/Arctic • Water mass transformation in the Nordic Seas • AMOC variability • Physical forcing of the marine biota • Idealised experiments; role of the ocean preconditioning and atmospheric forcing Have used NCAR/NCEP and ERA40, error in implementation of CORE; will be rerun
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Spin-up; monthly forcing; daily forcing; relaxation T and/or S Topics;
Spin-up; monthly forcing; daily forcing; relaxation T and/or S Topics; Variability guided by observed changes (mainly) in the Atlantic; particularly the gyre variability Inflow to t he Nordic Seas/Arctic Water mass transformation in the Nordic Seas AMOC variability - PowerPoint PPT Presentation
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Department of GeophysicsUniversity of Bergen
Spin-up; monthly forcing; daily forcing; relaxation T and/or S
Topics;• Variability guided by observed changes (mainly) in the Atlantic; particularly the gyre variability• Inflow to the Nordic Seas/Arctic• Water mass transformation in the Nordic Seas• AMOC variability• Physical forcing of the marine biota• Idealised experiments; role of the ocean preconditioning and atmospheric forcing
Have used NCAR/NCEP and ERA40, error in implementation of CORE; will be rerun
Department of GeophysicsUniversity of Bergen
Spin-up … min full 4 cycles with daily forcing; usually 6 full cycles (ca. 300 yr)
Always start with (strong) SSS-relaxation; 30 days for 50 m thick ML; scales with ML depth; limited to |ΔSSS<0.5| everywhere; no relaxation under max sea ice extent
Diagnose SSS-nudging when model is steady (5th or 6th cycle); applying diagnosed SSS-fluxes for the production runs with very weak Newtonian relaxation (360 days time scale for 50 m ML and |ΔSSS<0.5| )
Temperature relaxation is not critical (in our system)
2) Increased salinity in thesubtropical gyre (STG)
1) Relative contributionfrom the two gyres
(Dynamics)
4) Enhanced Evaporation minus Precipitation (E-P)
Possible mechanisms causing the rapid increase in salinity (and temperature)
Hatun et al., Science (2005)
Department of GeophysicsUniversity of Bergen
Altimetry
MICOM
SSH EOF (Häkkinen and Rhines, Science, 2004)
I
I
F
F
R
R
Dynamical SPG influence
Department of GeophysicsUniversity of Bergen
RI
A longer term perspective,using the simulated Gyre Index
as a proxy for the circulation
Irminger Current (obs)
Rockall Through (obs)
Gyre index (model)
Department of GeophysicsUniversity of Bergen
NB: Relationship also valid for temperature
Department of GeophysicsUniversity of Bergen
Forcing mechanisms (I)
Hatun et al., in prep.
Department of GeophysicsUniversity of Bergen Hatun et al., in prep
Forcing mechanisms (II)
Department of GeophysicsUniversity of Bergen
Wind stress and NAO consistent with the Gyre Index before - but not after - 1995
Department of GeophysicsUniversity of Bergen
– SPG is of key importance for the decadal-scale variations in the Atlantic inflow to the Arctic Mediterranean and along the cost off South Greenland
– The strength of the SPG is governed by the Subpolar (winter) buoyancy forcing
– The latter follows, in general, the North Atlantic wind stress (NAO) forcing, but not after 1995/96
– The Subpolar Gyre Index, rather than NAO, should be used as a proxy for the variability of the marine climate in the North Atlantic region (can be deduced from observations or hind-cast model simulations)
Conclusions (1)
Department of GeophysicsUniversity of Bergen
Recent North Atlantic Warming and Some Consequences Thereof
Helge Drange, Katja Lohmann, Mats Bentsen, Hjalmar Hatun, Anne Britt Sandø and colleagues