Parameterizing the Faroe Bank Channel (FBC) and Denmark Strait (DS) Overflows
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Parameterizing the Faroe Bank Channel (FBC) and Denmark Strait (DS)
OverflowsG. Danabasoglu, B. Briegleb and W.Large
(NCAR)WHAT HAVE WE DONE ? OWG 07
DOES IT WORK ? OWG 07
DOES IT MATTER ??? Today
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Uncoupled OGCM (~3 deg) Coupled CCSM (*) (T31x3)
Experiments• CON (*) : 200 year, “resolved” overflows
• FBC : 200 year, parameterized FBC
• DSO (*) : 200 year, parameterized DSO
RESULTS : (Years 181 - 200)
CON (*) - OBS (biases) DSO (*) - CON
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Matter ?
Temperatureat 2000m
CON-OBS
DSO alone removes muchof the North Atlantic biasfrom the Labrador Sea tothe South Atlantic
DSO-CON
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Matters ?Temperature
at 2000m
CCSM biases much smaller
CON*-OBS
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Matters ?Temperature
at 2000m
As hoped DSO impact positive, but not too big.
CON*-OBS
DSO*-CON*
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Temperatureat 500m CON-OBS
DSO-CON
DSO alone removes muchNorth Atlantic bias between 30 and 75° N .
Prognostic INFLOWis east of Iceland inN. A. Drift, not locallyin Denmark Strait
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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
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THE END
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Faroe-Bank Channel
Denmark Strait
Latitude
Domain for the regional simulations of FBC overflow (Riemenschneider)
Multiple Entrainments + Path
from J.Price
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Surface
-z
ATLANTIC NORDIC SEAS
MS = g’ (hS)2 / 2f
MS
2100m
945m
686m
BOTTOM TOPOGRAPHY
ME
MP
ρS
(Source density based on 12 grid points)
ρO
(density based on 12 grid points)
g’ = g (ρS-ρO)/ρref
MP = MS + ME
Heat and salt conservation
+
ρE
gE’ = g (ρS-ρE)/ρref
Entrainment
MSBC (Price and Yang)
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Working ?
MS , ME (Sv) 200 year Spin Up
FBC
DSO
MS
MS
ME
ME
3--
3--
1--
1--
2--
2--
Acceptable drifts
Final assessmentwhen run together
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Working ?
North AtlanticIdeal Age (181-200) DSO
DSO - CON
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Ocean Model for CCSM4 +:
• 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)
June 08, CCSM
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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)
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ANN aice NH
CCSM3 Low Viscosity
CCSM3-Low
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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), (x10 20-30º )
• Resolved Tropical Instability Waves (viscosity)
COUPLED IMPACTS
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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)
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BSF and T’ @ 175m
Fully coupled
Ocean alone,
60 lvl
Ocean-ice,
60 lvl
Ocean-ice,
100 lvl
North Atlantic Current
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Temperatureat 2000m
CON-OBS
DSO-CON
DSO alone removes muchof the North Atlantic biasfrom the Labrador Sea tothe South Atlantic
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Temperatureat 500m
CON-OBS
DSO-CON
DSO alone removes mostNorth Atlantic bias between 30 and 75° N .
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CCSM3.5 (26) CCSM3.5 (31)ZONAL WIND STRESS
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Observed CCSM3.5 (26)
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Observed CCSM3.5 (31)
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THE END
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Add Monday
• Slides on NAC from Steve
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Interior Diffusivity
SST bias
SST colors
SLP contours
No change toOcean PBL
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Temperatureat 3000m
CON-OBS
DSO-CON
DSO alone reduces North Atlantic biases
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MOC
Global AtlanticGlobal Atlantic
DSO
DSO-CON
Both deep downstreamand shallow upstreamresponses
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FV2x1
Low Viscosity
Higher Viscosity
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Tropical rainfall
biases in T42x1.
Difference in
rainfall between
high mixing and
control.
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CCSM3.5 (26) UW (30)ZONAL WIND STRESS
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Observed CCSM UW (30)UWpbl (30)
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Faroe-Bank Channel
Denmark Strait
Latitude
Domain for the regional simulations of FBC overflow (Riemenschneider)
Multiple Entrainments + Path
from J.Price
Parameterized Overflows
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Ideal Age (181-200)
DSO
DSO - CON
Young DSO watergoes deeper to 4000m