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Improved modeling of the Arctic halocline with a sub-grid-scale brine rejection parameterization

Improved modeling of the Arctic halocline with a sub-grid-scale brine rejection parameterization. Nguyen, An T., D. Menemenlis, R. Kwok, submitted to JGR Oceans. AOMIP results. [Holloway, 2007]. b ~ 200m. z ~ 40m.

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Improved modeling of the Arctic halocline with a sub-grid-scale brine rejection parameterization

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  1. Improved modeling of the Arctic halocline with a sub-grid-scale brine rejection parameterization Nguyen, An T., D. Menemenlis, R. Kwok, submitted to JGR Oceans AOMIP workshop #12 Jan 14-16, 2009 WHOI

  2. AOMIP results [Holloway, 2007] AOMIP workshop #12 Jan 14-16, 2009 WHOI

  3. b~200m z~40m Fig.4:Numerical result of salt rejected into a density-stratified fluid. The salt plume of horizontal extent b reaches the neutral buoyancy depth z before spreading out horizontally. Figure is taken from [Smith, 1998]. Previous Works Duffy et al. [1997, 1999] in the Southern Ocean: Antarctic Intermediate Water AOMIP workshop #12 Jan 14-16, 2009 WHOI

  4. b z Previous Works [Helfrich, 1994] [Smith and Morison, 1998] AOMIP workshop #12 Jan 14-16, 2009 WHOI

  5. b~200m z~40m Fig.4:Numerical result of salt rejected into a density-stratified fluid. The salt plume of horizontal extent b reaches the neutral buoyancy depth z before spreading out horizontally. Figure is taken from [Smith, 1998]. Brine Rejection • Sea-ice retains 33% of salt • 67% of salt rejected back to the ocean • Rejected salt s(z) is distributed down to bottom of mixed layer z=D according to: A: constant of normalization n, D: parameters to be determined AOMIP workshop #12 Jan 14-16, 2009 WHOI

  6. 04 Feb 1992 b~200m z~40m Fig.4:Numerical result of salt rejected into a density-stratified fluid. The salt plume of horizontal extent b reaches the neutral buoyancy depth z before spreading out horizontally. Figure is taken from [Smith, 1998]. Brine Rejection • Density structure: • dr/dz in mixed layer: 10-6 to 10-4 kg/m3/m • dr/dz @ top of halocline ~ 10-2 to 10-1 kg/m3/m AOMIP workshop #12 Jan 14-16, 2009 WHOI

  7. ECCO2: High- Resolution Global- Ocean and Sea-Ice Model b~200m z~40m Fig.4:Numerical result of salt rejected into a density-stratified fluid. The salt plume of horizontal extent b reaches the neutral buoyancy depth z before spreading out horizontally. Figure is taken from [Smith, 1998]. MITgcm • Ocean model: • ~ 18km horizontal, 50 vertical levels • volume-conserving, C-grid • Surface BC’s: ECMWF / ERA-40 based • Initial conditions: optimized • bathymetry: GEBCO • KPP mixing [Large et al., 1994] • Sea ice model: • C-grid, ~ 18km • 2-catergory zero-layer thermodynamics [Hibler, 1980] • Viscous plastic dynamics [Hibler, 1979] • Initial conditions: Polar Science Center • Snow simulation: [Zhang et al., 1998] AOMIP workshop #12 Jan 14-16, 2009 WHOI

  8. b~200m z~40m Fig.4:Numerical result of salt rejected into a density-stratified fluid. The salt plume of horizontal extent b reaches the neutral buoyancy depth z before spreading out horizontally. Figure is taken from [Smith, 1998]. ECCO2 Arctic Solution AOMIP workshop #12 Jan 14-16, 2009 WHOI

  9. b~200m z~40m Fig.4:Numerical result of salt rejected into a density-stratified fluid. The salt plume of horizontal extent b reaches the neutral buoyancy depth z before spreading out horizontally. Figure is taken from [Smith, 1998]. ECCO2 Arctic Solution AOMIP workshop #12 Jan 14-16, 2009 WHOI

  10. b~200m z~40m Fig.4:Numerical result of salt rejected into a density-stratified fluid. The salt plume of horizontal extent b reaches the neutral buoyancy depth z before spreading out horizontally. Figure is taken from [Smith, 1998]. Sensitivity Experiments Table.1 1: Nansen Basin 2: Amundsen Basin 3: Makarov Basin 4: Canadian Basin 5: Chukchi Cap Data: SCICEX 1993-2000 BGEP 2003-2004 AOMIP workshop #12 Jan 14-16, 2009 WHOI

  11. b~200m z~40m Fig.4:Numerical result of salt rejected into a density-stratified fluid. The salt plume of horizontal extent b reaches the neutral buoyancy depth z before spreading out horizontally. Figure is taken from [Smith, 1998]. A02006 Results: mixed layer depth Table.1 A01992 A0 A0’ 2006 A0’ 0m 50m AOMIP workshop #12 Jan 14-16, 2009 WHOI

  12. Table.1 b~200m z~40m Fig.4:Numerical result of salt rejected into a density-stratified fluid. The salt plume of horizontal extent b reaches the neutral buoyancy depth z before spreading out horizontally. Figure is taken from [Smith, 1998]. Results: Amundsen Basin SCICEX, 2000 AOMIP workshop #12 Jan 14-16, 2009 WHOI

  13. Table.1 b~200m z~40m Fig.4:Numerical result of salt rejected into a density-stratified fluid. The salt plume of horizontal extent b reaches the neutral buoyancy depth z before spreading out horizontally. Figure is taken from [Smith, 1998]. Results: Canadian Basin BGEP 2003 AOMIP workshop #12 Jan 14-16, 2009 WHOI

  14. Blue: off Red: on b~200m z~40m Fig.4:Numerical result of salt rejected into a density-stratified fluid. The salt plume of horizontal extent b reaches the neutral buoyancy depth z before spreading out horizontally. Figure is taken from [Smith, 1998]. Results: AOMIP workshop #12 Jan 14-16, 2009 WHOI

  15. b~200m z~40m Fig.4:Numerical result of salt rejected into a density-stratified fluid. The salt plume of horizontal extent b reaches the neutral buoyancy depth z before spreading out horizontally. Figure is taken from [Smith, 1998]. Concern: Heat content [Holloway, 2007] AOMIP workshop #12 Jan 14-16, 2009 WHOI

  16. b~200m z~40m Fig.4:Numerical result of salt rejected into a density-stratified fluid. The salt plume of horizontal extent b reaches the neutral buoyancy depth z before spreading out horizontally. Figure is taken from [Smith, 1998]. Summary • brine rejection: • realistic MLD (compared to climatology) • best fit to CTD observations in all basins • reproduces halocline • improve vertical stratification in Eurasian Basin • background diffusivity n = 10-5 m2/s •  too much artificial vertical mixing • reduce n eliminates vertical mixing •  optimized n = 10-7 m2/s AOMIP workshop #12 Jan 14-16, 2009 WHOI

  17. Coordinated experiment AOMIP workshop #12 Jan 14-16, 2009 WHOI

  18. b~200m z~40m Fig.4:Numerical result of salt rejected into a density-stratified fluid. The salt plume of horizontal extent b reaches the neutral buoyancy depth z before spreading out horizontally. Figure is taken from [Smith, 1998]. Model: A0’ 2006 Brine Rejection: • A package in the MITgcm • Mixed layer depth (MLD): determined based on dr/dr • When sea-ice forms  salt rejected  buoyancy terms in KPP  distribute buoyancy down to MLD • KPP, back-ground diffusivity n = 10-7 m2/s • Forcings: ERA40/ECMWF • BCs: WOA05 or global solutions • IC: WOA05 • 1992-2006 AOMIP workshop #12 Jan 14-16, 2009 WHOI

  19. b~200m z~40m Fig.4:Numerical result of salt rejected into a density-stratified fluid. The salt plume of horizontal extent b reaches the neutral buoyancy depth z before spreading out horizontally. Figure is taken from [Smith, 1998]. Data: • SCICEX 1993-2000 • BGEP 2003-2005 • ASOF 1996-2004 AOMIP workshop #12 Jan 14-16, 2009 WHOI

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