Kinematic Subduction RateOf
Labrador Sea Water
Peggy Courtois
Xianmin Hu, Yarisbel Garcia, Paul Myers
Earth and Atmospheric SciencesUniversity of Alberta
Alberta, Canada
Subduction Rate
h : mixed layer thickness
wb : vertical velocity at the base of the mixed layer
v. h▽ : advection terms
Aσ : outcrop area between σ and σ + δσ
σh : instantaneous mixed layer density.
* Rui Xin Huang’s book (Ocean Circulation)
2
Subduction Rate
ML
MLD
wb
v. h▽σh
δh/δt
Surface
Aσ(t):= [σ ≤ σh(x,t) ≤ σ+δσ]3
Subduction Rate
Classes:
27.68 - 27.74 kg.m-3
27.74 - 27.82 kg.m-3
27.82 - 27.92 kg.m-3
ULSW(t)
CLSW(t)
τ: integration over a year
4
Subduction Rate
MLD
Obduction
MLD(winter)
S < 0
MLD MLDSubduction
(summer)
S > 0
5
Arctic and Northern Hemisphere Atlantic (ANHA)
Model: NEMO 3.4, with LIM2 and EVP
Resolution : 1/12 degree
(LS ~ 5 km, CAA ~ 4 km)
Mesh : 1632 x 2400, 50 levels
Model Configuration
km
ANHA12
Xianmin Hu
Initialization: 3D T, S, U and V (GLORYS1v1, Jan02) Sea Ice
Atmospheric forcing (CGRF, hourly): T2, Q2, U10, V10 Precipitation Radiation (SW & LW) Snow: CORE2 (IA)
Runof: Dai and Trenberth climatology
OBC: U, V, T and S (GLORYS1v1)
NO temperature & salinity restoring
Jan 2002 – 2010
CGRF: CMC GDPS reforecasts CMC: Canadian Meteorological Centre
GDPS: Global Deterministic Prediction System GLORYS: GLobal Ocean ReanalYses and Simulations 6
Mixed Layer Depth
MLDNEMO = 2080.3 m
MLDTS = 771.9 m
Position:57.0721°N54.1838°W
January, 5th 2008
Similar method toHolte and Talley,
2009
7
Mixed Layer Depth
MLDNEMO
January, 5th 2008
MLDTS
January, 5th 2008
ARGO floats
September 2007To
May 20088
Water MassesClasses:
27.68 - 27.74 kg.m-3
27.74 - 27.82 kg.m-3
27.82 - 27.92 kg.m-3
ULSW(t)
CLSW(t)
2004, January 1st
T
S
PV
9
Subduction RateMLDNEMO
MLDTS δh/δtwb graduh gradvh
January, 5th 2008
10
Subduction Rate January, 5th 2008
MLDNEMO MLDTS
δh/δt
v. h▽wb
11
Subduction Rate
MLDNEMO
MLDTS
Subduction rate versus the density averaged over
2002-2010
12
Subduction Rate
Ann. mean
-1.3 Sv
0.8 Sv
6.8 Sv
3.9 Sv
7.9 Sv
13
MLDNEMO
Subduction Rate
Ann. mean
-0.3 Sv
1.5 Sv
4.4 Sv
1.9 Sv
4.1 Sv
14
MLDTS
Subduction Rate27.68 - 27.74 kg.m-3
27.74 - 27.82 kg.m-3
27.82 - 27.92 kg.m-3
MLDNEMO
MLDTS
Annual mean
6.4 Sv
5.6 Sv
15
Conclusion
16
Paul's team:
Nathan, Laura G, Laura CG, Tilia, Vasco, Georg,
Yongxing, Natasha, Ting, Juliana, Clark
● Large impact on the MLD over the net subduction rate when different water masses are considered
● Not a large impact on the annual mean
● Labrador Sea Water formation of 5.6 Sv and 6.4 Sv depending on the MLD
● On going: Quantifying the impact of each component on the subduction rate
Thanks!
Subduction Rate
Subduction Rate
Subduction Rate
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