Environmental forces acting on oil at sea surface

[loupote]

Hi!

I’m trying to configure an oil drift simulation and need to understand what data to import. However, after spending some time reading the literature, I’ve become confused about the environmental effects on an oil particle.

From what I understand, wind at the sea surface generates waves that lead to a net mass transport — this is known as the Stokes drift. I read that it is the main reason for the strong velocity that decreases with depth, but is it correct to call it a current?

When x_sea_water_velocity data are measured, do they refer to the Stokes drift? Do they include it, or is it a separate current?

In other words, in the calculation of a particle’s velocity U = U_current + alpha*U_wind + U_Stokes, are U_current and U_Stokes really different ?

Thanks!

[AndresSepulveda]

Hi,

It all depends if the calculated U_current was done using a model that inclued wave forcing. Most models results don't. In that case it would be useful to add the wave effect with U_Stokes

[knutfrode]

Yes, if ocean model is coupled to a wave model, the Coriolis-Stokes effect may influence the current calculated.

However, this is not the same as the Stokes drift itself, which is not a Eulerian current, but a Lagrangian effect.

Thus x_sea_water_velocity/x_sea_water_velocity may implicitly contain the Coriolis-Stokes effect, but never the Stokes drift.
The Stokes drift must be added explicitly, and also in addition to an empirical 2% windage at surface.
Or, what is very common, one can omit the Stokes drift (and the need for a wave model), and instead increase the windage to ~3.5%
The surface Stokes drift is to a good approcimation 1.5% of the wind at the very surface.