1. Ocean surface currents and the Craig-Banner boundary condition Charles Tang Bedford Institute of Oceanography Dartmouth, Nova Scotia, Canada POM for the Labrador Sea and eastern Canadian shelves Simulations of circulation and winter convection Wind-driven currents on the Grand Banks Testing of the Craig-Banner boundary condition Wave-current interaction

5. Short-term forecasts of surface currents 2-day forecasts wind-driven currents no data assimilation comparison with surface drifter trajectories Questions: Representation of surface currents in POM Wave effects

7. Low -wind condition

8. Strong winds

10. Turbulence closure model in POM Forcing by constant wind stress

11. 25-day simulations red - original boundary condition black - Craig-Banner boundary condition

12. q2 - turbulent kinetic energy KmKm

13. Application of theories of wave-induced currents Weber, J., Steady wind- and wave-induced currents in the open ocean. JPO, 1983. Jenkins, A.D., A theory for steady and variable wind- and wave-induced currents. JPO, 1986. Jenkins, A.D., Wind and wave induced currents in a rotation sea with depth- varying eddy viscosity. JPO, 1987. Jenkins, A.D., The use of a wave prediction model for driving a near-surface current model. Dt.Hydrogra.Z, 1989. Weber, J. & A. Melsom, Transient ocean currents induced by wind and growing waves. JPO, 1993.

14. Wave effects on surface currents The Stokes drift Modification of diffusivity due to wave breaking Partition of wind momentum for generation of waves and currents

15. Representation of the Stokes drift (1) Single wave (Stokes, 1847) (2) Wave field (Jenkins, 1989) (3) Parameterization by wind speed (Wu, 1983)

16. Model currents with the Stokes drift

17. Momentum equation for the Ekman layer and boundary condition Equation for wave energy spectrum

18. Vertically integrated Ekman equation

19. Drifter data show surface currents in the direction of wind vectors during strong winds. The Craig-Banner boundary condition increases the turbulent kinetic energy and mixing intensity at the surface, and reduces surface currents. A formulation based on Jenkins’ theory of wave-current interaction is proposed to calculate surface currents. Summary POM simulates seasonal-scale variables in the Labrador Sea reasonably well, but produces surface currents not always in agreement with observations in short-term forecasts.