water mass transformations in the indonesian throughflow ariane koch-larrouy, gurvan madec, robert...
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Water mass transformations in the Indonesian Throughflow
Ariane Koch-Larrouy, Gurvan Madec, Robert Molcard
Parameterization in an OGCM of the mixing in the ITF : Effect on Water masses
> Only low latitude passage between two oceans Only low latitude passage between two oceans => key region for circulation and climate=> key region for circulation and climate
> fresh and cool water flow from Pacific Ocean to Indian Oceanfresh and cool water flow from Pacific Ocean to Indian Ocean
1. Introduction
In situ Observations (Gordon 2005)
1. Cruise> Only low latitude passage between two oceans Only low latitude passage between two oceans => key region for circulation and climate=> key region for circulation and climate
> Cruises to understand variability and characteristics of this Cruises to understand variability and characteristics of this flow : JADE, ARLINDO, INSTANTflow : JADE, ARLINDO, INSTANT
INSTANT (2004-2007), R. Molcard, A. Atmadipoera at the LOCEAN (+ 300 Indonesian CTD recovered)
1. Water masses transformation
Mixing is necessary but where ?
Advection diffusion model -> Kz ~ 1-2 cm2/s Ffield & Gordon 92
WODB 2001 data
makassar
banda
ceram
halmahera
WHERE ? WHERE ?
WHY ? WHY ?
because of what because of what
phenomenaphenomena
is the ITF transformed is the ITF transformed
1. Objectives Tools
OPA-NEMO (OGCM) OPA-NEMO (OGCM)
1/4th degree 1/4th degree
open boundaries open boundaries
tke (wind & shear param)tke (wind & shear param)
2d internal tides generation model2d internal tides generation model
Results from tidal modelResults from tidal model
1. Results
Mixing may occur preferentially above rough topography
Solve the explicit tides ? Schiller 2004 & Robertson
2006
Show that internal tides could and must be responsible for the mixing
Did not look precisely at the effect on water masses Hard to link the breaking to the mixing
Our strategy :
Parameterization of the effects of the tides
1. What do we know ?
60 cm2/s 0.1 cm2/s
2D internal tides model
Microstructure measurement
Alford et al.Hatayama 2004
Where ? Why ?
bottom friction
Internal tide generated
1. Internal tides
Internal wave drag
2 sinks of the tidal energy
Energy transfered to barotropic tides to baroclinic tides
bottom friction
Internal tide generated
Internal wave drag from tidal model
Le provost & Lyard 2002
1. Internal Tides
Internal wave drag
This energy transfer is 20 times more concentrated in the ITF than over the global ocean
Lyard & Le Provost
bottom friction
Internal tide generated
1. Internal Tides
Internal wave drag
ITF = unic region in the world
- 20 times more concentrated than for global ocean - semi enclosed sea => all the energy is avalaible for dissipation
0.11 TW
1.1 TW
1. parameterization
St Laurent 2002
E(x,y)
F(z)
Where on the horizontal ?
Where on the vertical ?
q
How much is dissipated ?
ITF specificities
E(x,y)
F(z)
1. parameterization
St Laurent 2002
Where on the horizontal ?
Where on the vertical ?
q
How much is dissipated ?
q tidal dissipation efficiency
All the energy available for mixing q = 1
Complex topography, series of semi enclosed sea.Once generated internal tides remain confined
E(x,y)
F(z)
Highly heterogeneous Maximum of energy in Maluku and Halmahera Seas
1. parameterization
St Laurent 2002
Where on the horizontal ?
Where on the vertical ?
q = 1
How much is dissipated ?E(x,y) drag coefficient from tidal model
2 tests - E(x,y) averaged - E(x,y) apply locally
Maximum of energy in the thermocline
E(x,y)
F(z)
1. parameterization
St Laurent 2002
Where on the horizontal ?
Where on the vertical ?
q = 1
How much is dissipated ?
T. Gerkema &P. Bouruet AbertotInternal tidal model 2D
F(z)~N
F(z)~N2
F(z) vertical structure of the energy to be dissipated
1. Results
1. Results
- ITF strong internal tides, trapped in the different semi-enclosed seas
- build a parameterization of 3d varying kz
- average kz = 1.5 cm2/s, independently agrees with the estimates inferred from observations, suggesting that tides are a major phenomenon for the water masses transformation.
- the parameterization improves the water masses characteristics in the different Indonesian seas, suggesting that the horizontal and vertical distributions of the mixing are adequately prescribed.
- Role of Dewakang sill and Halmahera and Seram seas in mixing
1. Conclusion parameterization
4. Conclusion parameterization development of a new parameterization taking into account internal tides in an OGCM specific to Indonesian region that reproduce well the water masses and their transformations.
mixing due to internal tides is a major phenomenon explaining the strong transformation of water masses in the ITF
Inter-annual Variability G70 DRAKKAR, comparison with data (INSTANT, …)
Impact of the mixing on a coupled model. Does it modify the atmospheric convection ?
Questions ?Questions ?