Internal tides in NEMO in the Indonesian seas. A. Koch-Larrouy, D. Nugroho, F. Lyard, D. Allain, B. Tranchant, P. Gaspar, J.

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1 Internal tides in NEMO in the Indonesian seas A. Koch-Larrouy, D. Nugroho, F. Lyard, D. Allain, B. Tranchant, P. Gaspar, J. Chanut

2 Indonesian archipelago = strong Internal tides mixing Advection diffusion model -> strong vertical mixing temperature Kz ~ 1-2 cm 2 /s Hautala et al 1996, Ffield et Gordon 1996 = 10 times > open ocean Best candidate : Internal tides salinity

3 How to take into account internal tides in an OGCM? Surface Barotropic tides Fond Topographie I. Generation II. Propagation III. Breaking IV. Dissipation Horizontal scale ~10000 km Barotropic tides km 10-1 km 10-1 m cm/mm Internal tides Non lineary waves Breaking waves Dissipation /Diffusion

4 Surface How to take into account internal tides in an OGCM? Parameterize Internal tides Barotropic tides Fond Topographie I. Generation II. Propagation III. Breaking IV. Dissipation 0.2 E(x,y) F(z) k z tides = N 2 St Laurent et al Horizontal scale ~10000 km Barotropic tides km 10-1 km 10-1 m cm/mm Internal tides Non lineary waves Breaking waves Dissipation /Diffusion

5 Parameterize Internal tides k z tides = 0.2 E(x,y) F(z) N GW Lyard et al. 2006

6 How to take into account internal tides in an OGCM? Explicite forcing Surface Internal tides Barotropic tides Fond Topographie I. Generation II. Propagation III. Breaking IV. Dissipation OGCM Horizontal scale ~10000 km Barotropic tides km 10-1 km 10-1 m cm/mm Internal tides Non lineary waves Breaking waves Dissipation /Diffusion

7 How to take into account internal tides in an OGCM? Explicite forcing Surface Internal tides Barotropic tides Fond Topographie I. Generation II. Propagation III. Breaking IV. Dissipation Partly Partly OGCM NOT RESOLVED Horizontal scale ~10000 km Barotropic tides km 10-1 km 10-1 m cm/mm Internal tides Non lineary waves Breaking waves Dissipation /Diffusion Need new param

8 of internal tides I. Generation Barotropic tides Baroclinic Tidal Energy Conversion Rate in Terra Watt Resolving explicite 1 90 % 80 % 75 % % Partly resolve GENERATION of internal tides /36 1/24 1/12 9km Grid Spacing ( x 1/60 Degree ) /4 30km 3 5 Niwa and Hibiya,2013

9 More and more studies includes explicit tidal forcing Indonesian Castruccio et al. (2013); Kartadikaria et al. (2011); Nagai and Hibiya (2015) Global Niwa and Hibiya (2001b); Jan et al. (2008); Wang et al. (2016); Alford et al. (2015) Niwa and Hibiya (2011); Arbic et al. (2012); Simmons et al. (2004); Shriver et al. (2012)

10 How the model reproduce mixing? >objectif : quantify sinks of tidal energy in the model > think of idea for future parameterization of dissipation of internal tides

11 Tools INDESO NEMO 9km / FES2014 COMODO NO friction TUGO-m 1km NEMO 1km Tides only : - Barotrope - Barocline Realiste NEMO Smagorinsky Momentum UBS (very diffusive) Vertical viscosity Tracer TVD (diffusive) TUGO (spectral) Non diffusive

12 Tools INDESO NEMO 9km / FES2014 NEMO Ocean General Circulation Model 50 vertical layers Tke turbulent closure FES TUGO-m Hydrodynamical model, shallow water Tides only : - Barotrope - Barocline Realiste

13 fig3 FES2014 NEMO M2 K1 Sea surface height amplitude (cm) for M2 (upper) and K1 (lower).

14 Barotropic flux Baroclinic flux

15 fig5

16 GENERATION NEMO FES % of the expected FES2014 generation

17 Estimation of dissipation h v Friction

18 Barotrope 542 GW Barocline 475 GW Realist 450 GW

19 FES2014 Self Attraction Loading Friction 294 GW 54 GW INPUT = 777 GW TOTAL energy loss = 745 GW NEMO Barotrope INPUT = 707 GW TOTAL energy loss = 542 GW Unquantified Energy loss of 150

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21 TOTAL LOCAL NEAR FAR 50% locally 35% Near ffield 15% Far field

22 Mettre carte avec station St2 St3 St4 St5 St1

23 COMODO Test case #2: uniform N, No friction time-averaged energy diagnostics (energy fluxes) barotropic energy flux Cliquez et modifiez le titre baroclinic energy flux barotropic energy flux divergence baroclinic energy flux divergence

24 Baroropic flux Baroclinic flux

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26 Conclusions (work in progress) NEMO 1/12 is able to reproduce 75% of generation Friction good agreement with FES2014 Vertical dissipation mainly bottom Horizontal dissipation in the interior, out of which 50% away from generation site INDOMIX Above strait : very good Far field : too much COMODO non diffusive Numerical dissipation for barotropic tides over the abyssal plain Baroclinic tides? Time stepping? Normal modes separation Better than classical averaged method

27 How to take into account internal tides in an OGCM? Explicite forcing Surface Internal tides Barotropic tides Fond Topographie I. Generation II. Propagation III. I. Breaking IV. Dissipation NEED NEW PARAMETRIZATION OGCM Horizontal scale ~10000 km Barotropic tides km 10-1 km 10-1 m cm/mm Internal tides Non lineary waves Breaking waves Dissipation /Diffusion

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29 Separate Barotrope / Barocline Classical averaged method Normal modes method Depth integrated Barotropic flux Depth integrated Baroclinic flux

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31 Amplitude Phase Methode projection en mode normaux Mode 0 TUGO-m Mode 1 NEMO Mode 2 Mode 3 Mode 4 Mode 5

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33 Eps_h Eps_z BT BC

34 Isopycnal Displacement layer 26, 200m, day 15, July(summer) (a) M2 (b) S2 (c) K1 (d) O1

35 Rate Of Work Rate Of Work Rate Of Work BAROCLINE BAROTROPE FES2014 Pot Astro Self Attraction Loading