Wind surface stress

Wind stress is calculated according to a quadratic friction law:

$\overrightarrow{{\tau_w}} = C_D \cdot \rho_a \cdot \overrightarrow{W}|\overrightarrow{W}|$

where $C_D$ is a drag coefficient that is function of the wind speed, $\rho_{a}$ is air density and $\overrightarrow{W}$ is the wind speed at a height of 10 m over the sea surface.