# Stokes's drift velocity

From AMS Glossary

## Stokes's drift velocity

To the order of the square of the wave amplitude, it is where <·> represents the average over a wave period, where

*t*is time,**u**is the local (Eulerian) velocity of the wave motion, and**x**is the position of the fluid particle at*t*=*t*_{0}. As an example, for surface gravity waves of a homogeneous ocean with a flat bottom,*a*is the wave amplitude,**k**is the wavenumber vector,*k*= , ω is the wave frequency,*z*is the vertical coordinate (negative below the ocean surface), and*H*is the depth of the ocean.