Response of water temperature to surface wave effects: experiments with the coupled NEMO-WAM

Transcription

1 Response of water temperature to surface wave effects: experiments with the coupled NEMO-WAM Victor Alari (HZG), Joanna Staneva (HZG), Sebastian Grayek (HZG) and Oyvind Breivik (ECMWF/Norwegian Met. Institute) Baltic Earth Doctoral Conference, Tartu, Estland 11. August 2015

2 Outline Motivation and objective Model setup for the North Sea-Baltic Sea Physical processes forming wave-circulation interaction Wave impact to temperature Conclusions

3 Motivation and objective Traditionally ocean models and wind wave models have been applied separately. Separating wave and ocean models is pragmatic, but leads to violation of energy and momentum conservation. During EU-FP7 project MyWave a coupled global scale wave-circulation model was developed (Breivik et al, 2015). Applying the coupled model to World Ocean, a reduction of bias between modelled and measured SST was noted. The overall aim of our research is to study the impact of wind waves to the Baltic Sea and North Sea water dynamics.

4 Outline Motivation and objective Model setup for the North Sea-Baltic Sea Physical processes forming wave-circulation interaction Wave impact to temperature Conclusions

5 Model setup (1): geographical view Blue solid lines model open boundaries Blue dashed box our analysis area Red dashed lines vertical transects

6 Model setup (2) : key information EC-NEMO EC-WAM Modelling period Switched on at Horizontal grid 2 NM covering North Same Sea and Baltic Sea Vertical grid 21 s layers, emphasis on N/A Initial field Janssen climatology Zero for T & S Boundary condition OSU tides, Janssen periodic boundary No Atmospheric forcing German Weather Same Service (DWD), 1 h. Vertical diffusion GLS (k-eps) N/A scheme Ice LIM2 No ice Bottom friction coef Log-layer Const

7 Outline Motivation and objective Model setup for the North Sea-Baltic Sea Physical processes forming wave-circulation interaction Wave impact to temperature Conclusions

8 Physical processes forming wave-circulation interaction (1) 1) Stokes-Coriolis forcing 2) TKE due to breaking waves 3) Ocean side stress NEMO WAM Currents Breivik, O., Mogensen, K., Bidlot, J.- R., Balmaseda, M.A., Janssen, P.A.E.M. Surface wave effects in the NEMO ocean model: Forced and coupled experiments (2015) Journal of Geophysical Research C: Oceans, 120 (4), pp

9 Physical processes forming wave-circulation interaction (2): Stokes-Coriolis forcing For the calculation of vertical Stokes profile, see: Breivik, Ø., Janssen, P.A.E.M., Bidlot, J.-R. Approximate stokes drift profiles in deep water (2014) Journal of Physical Oceanography, 44 (9), pp

10 Physical processes forming wave-circulation interaction (3): TKE due to breaking waves In uncoupled NEMO, alfa is constant=100

11 Physical processes forming wave-circulation interaction (4): ocean side stress U t fv = gh ξ x + τ x τ xb V t + fu = gh ξ y + τ y τ yb

12 Physical processes forming wave-circulation interaction (5): ocean side stress U t fv = gh ξ x + τ x τ xb U t fv = gh ξ x + τ ocx τ xb V t + fu = gh ξ y + τ y τ yb V t + fu = gh ξ y + τ ocy τ yb

13 Physical processes forming wave-circulation interaction (6): ocean side stress

14 Outline Motivation and objective Model setup for the North Sea-Baltic Sea Physical processes forming wave-circulation interaction Wave impact to temperature Conclusions

15 Results (1): wave validation at NBP

16 Results (2): comparison to climatology

17 Results (3): Arkona basin, water temperature Black line BUOY Blue line NEMO without waves Red line NEMO with WAVES

18 Results (4): Gotland Basin

19 Results (5): Impact of waves to SST

20 Results (6): Impact of waves to bottom Temp.

21 Results (7): Impact of waves, vertical/meridional

22 Results (8): Impact of waves, vertical/zonal

23 Conclusions For the first time, a coupled NEMO-WAM model has been setup and applied for the North Sea-Baltic Sea. The absolute warming or cooling due to waves on a seasonal basis is up to 1 0 C, instantaneous differences reach 5 0 C. When waves are accounted for, the bias of SST reduces systematically. Our study is as a step towards further developing new coupled ocean forecasting systems for the Baltic Sea area. The coupled system paws the road to a more realistic simulation of long-term variability of the Baltic Sea.

24 Thank You for your attention