AOMIP workshop #12 Jan 14-16, 2009 WHOI
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
AOMIP results
[Holloway, 2007]
AOMIP workshop #12 Jan 14-16, 2009 WHOI
Previous Works
Duffy et al. [1997, 1999] in theSouthern Ocean: AntarcticIntermediate Water
AOMIP workshop #12 Jan 14-16, 2009 WHOI
Previous Works
z
b
[Smith and Morison, 1998][Helfrich, 1994]
AOMIP workshop #12 Jan 14-16, 2009 WHOI
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
Dz
DzAzzs
n
,0
,)(
AOMIP workshop #12 Jan 14-16, 2009 WHOI
Brine Rejection
• Density structure: d/dz in mixed layer:
10-6 to 10-4 kg/m3/m d/dz @ top of halocline
~ 10-2 to 10-1 kg/m3/m
04 Feb 1992
AOMIP workshop #12 Jan 14-16, 2009 WHOI
MITgcm
ECCO2: High- Resolution Global- Ocean and Sea-Ice Model
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
ECCO2 Arctic Solution
AOMIP workshop #12 Jan 14-16, 2009 WHOI
ECCO2 Arctic Solution
AOMIP workshop #12 Jan 14-16, 2009 WHOI
Sensitivity Experiments
Table.1
1: Nansen Basin2: Amundsen Basin3: Makarov Basin4: Canadian Basin5: Chukchi Cap
Data:SCICEX 1993-2000BGEP 2003-2004
AOMIP workshop #12 Jan 14-16, 2009 WHOI
Results: mixed layer depth
A0’
0m 50m
A0
Table.1
A0’2006
A02006
A01992
AOMIP workshop #12 Jan 14-16, 2009 WHOI
Results: Amundsen Basin
Table.1
SCICEX, 2000
AOMIP workshop #12 Jan 14-16, 2009 WHOI
Results: Canadian Basin
Table.1
BGEP 2003
AOMIP workshop #12 Jan 14-16, 2009 WHOI
Results:
100
0
]'2'0,21[0
A
AA
SSQ
SSQSSQI
Blue: offRed: on
AOMIP workshop #12 Jan 14-16, 2009 WHOI
Concern: Heat content
[Holloway, 2007]
AOMIP workshop #12 Jan 14-16, 2009 WHOI
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 = 10-5 m2/s too much artificial vertical mixing
• reduce eliminates vertical mixing optimized = 10-7 m2/s
AOMIP workshop #12 Jan 14-16, 2009 WHOI
Coordinated experiment
AOMIP workshop #12 Jan 14-16, 2009 WHOI
Model:
KPP, back-ground diffusivity = 10-7 m2/s Forcings: ERA40/ECMWF BCs: WOA05 or global solutions IC: WOA05 1992-2006
Brine Rejection: A package in the MITgcm Mixed layer depth (MLD): determined based on d/dr When sea-ice forms
salt rejected buoyancy terms in KPP distribute buoyancy down to MLD
A0’2006
AOMIP workshop #12 Jan 14-16, 2009 WHOI
Data: SCICEX 1993-2000 BGEP 2003-2005 ASOF 1996-2004
