Etudes et évaluation de processus océaniques par des hiérarchies ...

194
20 CHAPTER 4. SURFACE FLUXES, THE FORCING OF THE OCEAN
This empirical formulas can at best be seen as a sophisticated rule of thump. Note that the
drag coefficient increases with wind speed. This is due to the larger roughness (waves) of the
ocean surface with higher winds.
Uncertainties in the determination of the wind stress are a major difficulty in modelling the
ocean dynamics.
Exercise 10: Search the Internet for a map of the wind shear of the world ocean.
4.4 What about tides?
tel-00545911, version 1 - 13 Dec 2010
The tidal dynamics varies on time scales that are very short compared to the large scale circulation
relevant for climate issues and has no direct dominant influence on the long-term
large-scale dynamics of the ocean. Tides do however substantially affect the large scale circulation
by increasing the vertical mixing of the ocean due to the interaction of tidal motion and
topographic features of the ocean basin. The tidal energy used to vertically mix the ocean is
however difficult to estimate, as are the locations where this mixing occurs. These questions
are actually an important subject of research in physical oceanography.