1. Parameterizing the Faroe Bank Channel (FBC) and Denmark Strait (DS) Overflows
G. Danabasoglu, B. Briegleb and W.Large
(NCAR)
WHAT HAVE WE DONE ? OWG 07
DOES IT WORK ? OWG 07
DOES IT MATTER ??? Today

2. Uncoupled OGCM (~3 deg) Coupled CCSM (*) (T31x3) Experiments
CON (*) : year, “resolved” overflows
FBC : year, parameterized FBC
DSO (*) : year, parameterized DSO
RESULTS : (Years )
CON (*) - OBS (biases)
DSO (*) - CON

3. Matter ? Temperature at 2000m
CON-OBS
DSO alone removes much
of the North Atlantic bias
from the Labrador Sea to
the South Atlantic
DSO-CON

4. Matters ? Temperature at 2000m
CON*-OBS
CCSM biases much smaller

5. Matters ? Temperature at 2000m
CON*-OBS
As hoped DSO impact
positive, but not too big.
DSO*-CON*

6. Temperature at 500m CON-OBS DSO alone removes much
North Atlantic bias between
30 and 75° N .
DSO-CON
Prognostic INFLOW
is east of Iceland in
N. A. Drift, not locally
in Denmark Strait

7. Conclusion : These positive results justify ;
Generalization for multiple overflows, higher resolution, SE standards
Evaluate coupled climate impact of parameterized overflows by comparing CFC uptake to observations
Effect on North Atlantic Circulation & Sea-Ice
Include Antarctic shelves

8. THE END

9. Denmark Strait Faroe-Bank Channel Latitude from J.Price
Multiple Entrainments + Path
Latitude
Domain for the regional simulations of FBC overflow (Riemenschneider)
from J.Price

10. MSBC (Price and Yang) ATLANTIC NORDIC SEAS Surface ρO ρS MS-z ρO
(density based on 12 grid points) ρS
(Source density based on 12 grid points)
686m MS
g’ = g (ρS-ρO)/ρref
945m
gE’ = g (ρS-ρE)/ρref ρE ME
MS = g’ (hS)2 / 2f
Entrainment
MP = MS + ME +
Heat and salt conservation MP
BOTTOM TOPOGRAPHY
2100m

11. Working ? MS , ME (Sv) 200 year Spin Up
FBC
3-- MS
2-- ME
1--
Acceptable drifts
Final assessment
when run together
DSO
3-- MS
2-- ME
1--

12. Working ? North Atlantic Ideal Age (181-200)
DSO
DSO
- CON

13. Ocean Model for CCSM4 +: Ocean Carbon Cycle (ecosystem)
June 08, CCSM
Ocean Carbon Cycle (ecosystem)
Reduced sea ice extent in Arctic margins
Improved equatorial ocean physics (ENSO)
Slower Antarctic Circumpolar Current
Cooler coastal SSTs (eastern boundaries)
Deeper North Atlantic Overturning
Warmer North Atlantic SST (Gulf Stream)

14. Review CCSM3 to CCSM3.5 Ocean BGC, Carbon-cycle
Extension of GM90 eddy parameterization to mixed-layers with a strong depth dependency
( CLIVAR Eddy-Mixed Layer CPT )
Increase vertical levels from 40 to 60
Greatly reduced lateral viscosity
(Key to CCSM3 & FV excess sea-ice problem)

15. ANN aice NH
CCSM3
Low Viscosity
CCSM3-Low

16. Equatorial physics (coupled)
Extend observationally based tidal mixing to shallow seas (e.g. Banda Sea)
Latitudinal dependent internal wave mixing in the ocean interior (1/10 tropics and Arctic), (x º )
Resolved Tropical Instability Waves (viscosity)
COUPLED IMPACTS

17. Ongoing to CCSM4 and beyond
Final decisions will depend on CAM (PBL) !!!
Optimizing 60 levels. 
Parameterization of sub-mesoscale re-stratification. 
Consistent PBL (atm, ocn) and flux (air-sea, air-ice, air-land) stability functions. 
Diurnal cycle of SST. (prototyped)
Parameterized deep overflows. (generalizing)
Nested regional models (coasts, ITF). (1 way)
Coastal ecosystems at higher trophic levels. (planning)

18. North Atlantic Current
BSF and 175m
North Atlantic Current
Fully coupled
Ocean alone,
60 lvl
Ocean-ice,
60 lvl
Ocean-ice,
100 lvl
Water columns which are destabilized by an upper ocean salinity gradient are conducive to the phenomenon of convective spice injection, which is discussed in detail in a paper that was published last year. This is a cartoon from that paper which demonstrates the essential aspects of the mechanism. We start with an early winter water column which is destabilized by salinity, so that it has a negative slope when plotted in salinity-density coordinates. Salinity is high at the surface (and mixed layer which is a singularity indicated by the square) and decreases with increasing density. The slope in these coordinates defines the Turner angle… a horizontal profile would correspond to Tu=45, indicating that the stratification is purely a function of temperature. A vertical profile in these coordinates would indicate a perfectly density-compensated water column with zero stratification, but with a large salinity gradient. When penetrative convective mixing driven purely by surface heat loss acts on such a water column, with a level of buoyancy entrainment consistent with observations and large eddy simulations, the resulting profile will rotate as shown as the sea surface density increases. The latter profile corresponds to late winter which we’ll define as the time of maximum SSD. In the results which follow, the early winter profile will correspond to a time roughly two months prior to the time of maximum SSD. So, the essential aspects of the mechanism are summarized here. Each of these bullets is in fact saying the same thing… diapycnal fluxes in such a profile rotate the profile, increase Tu, and inject spice. Injection of positive spice is evident as a positive increase in S (and T!) on a range of subducted isopynals in the transition layer.
S* = g[S - S1(0)]/(N12h1)
* = -[B - B1(0)]/(N12h1)
In S- coordinates, the generation of the strongly density compensated layer results in a clockwise rotation of the profile which reflects the higher Turner angles of the water column. Note that a vertical profile in these coordinates would indicate perfect density compensation.
Spice injection on subsurface isopycnals is evident as increases in salinity (and hence temperature) on a range of density surfaces which have not outcropped (vertical change in S1 to S2)

19. Temperature at 2000m CON-OBS DSO alone removes much
of the North Atlantic bias
from the Labrador Sea to
the South Atlantic
DSO-CON

20. Temperature at 500m CON-OBS DSO alone removes most
North Atlantic bias between
30 and 75° N .
DSO-CON

21. ZONAL WIND STRESS
CCSM3.5 (26)
CCSM3.5 (31)

22. Observed
CCSM3.5 (26)

23. Observed
CCSM3.5 (31)

24. THE END

25. Add Monday
Slides on NAC from Steve

26. Interior Diffusivity SST colors SLP contours No change to Ocean PBL
SST bias

27. Temperature at 3000m CON-OBS DSO alone reduces North Atlantic biases
DSO-CON

28. MOC DSO Both deep downstream and shallow upstream responses Atlantic
Global
Global
Atlantic
DSO-CON

29. FV2x1
Low Viscosity
Higher Viscosity

30. Tropical rainfall
biases in T42x1.
Difference in
rainfall between
high mixing and
control.

31. ZONAL WIND STRESS
CCSM3.5 (26)
UW (30)

32. Observed
UWpbl (30)
CCSM UW (30)

33. Parameterized Overflows
Denmark Strait
Faroe-Bank Channel
Multiple Entrainments + Path
Latitude
Domain for the regional simulations of FBC overflow (Riemenschneider)
from J.Price

34. Ideal Age ( )
DSO
Young DSO water
goes deeper to 4000m
DSO - CON