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{{short description|Average velocity of a fluid parcel in a gravity wave}}
{{Multiple image▼
| image1 = Deep water wave.gif▼
| direction = vertical▼
| width = 350▼
| caption1 = Stokes drift in deep [[water waves]], with a [[wave length]] of about twice the water depth.▼
| image2 = Shallow water wave.gif▼
| caption2 = Stokes drift in shallow water waves, with a wave length much longer than the water depth.▼
| footer = The red circles are the present positions of massless particles, moving with the [[flow velocity]]. The light-blue line gives the [[path (topology)|path]] of these particles, and the light-blue circles the particle position after each [[wave period]]. The white dots are fluid particles, also followed in time. In the cases shown here, the [[mean]] Eulerian horizontal velocity below the wave [[trough (physics)|trough]] is zero.<br>▼
Observe that the [[wave period]], experienced by a fluid particle near the [[free surface]], is different from the [[wave period]] at a fixed horizontal position (as indicated by the light-blue circles). This is due to the [[Doppler shift]].▼
}}▼
[[File:Driftwood Expanse, Northern Washington Coast.png|thumb|350px|right|An expanse of [[driftwood]] along the northern [[coast]] of [[Washington state]]. Stokes drift – besides e.g. [[Ekman drift]] and [[geostrophic current]]s – is one of the relevant processes in the transport of [[marine debris]].<ref>See [[#Kubota1994|Kubota (1994)]].</ref>]]
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==Mathematical description==
▲{{Multiple image
▲| image1 = Deep water wave.gif
▲| direction = vertical
▲| width = 350
▲| caption1 = Stokes drift in deep [[water waves]], with a [[wave length]] of about twice the water depth.
▲| image2 = Shallow water wave.gif
▲| caption2 = Stokes drift in shallow water waves, with a wave length much longer than the water depth.
▲| footer = The red circles are the present positions of massless particles, moving with the [[flow velocity]]. The light-blue line gives the [[path (topology)|path]] of these particles, and the light-blue circles the particle position after each [[wave period]]. The white dots are fluid particles, also followed in time. In the cases shown here, the [[mean]] Eulerian horizontal velocity below the wave [[trough (physics)|trough]] is zero.<br>
▲Observe that the [[wave period]], experienced by a fluid particle near the [[free surface]], is different from the [[wave period]] at a fixed horizontal position (as indicated by the light-blue circles). This is due to the [[Doppler shift]].
▲}}
The [[Lagrangian and Eulerian coordinates|Lagrangian motion]] of a fluid parcel with [[position vector]] ''x = '''ξ'''('''α''', t)'' in the Eulerian coordinates is given by<ref name=Phil1977p43>See [[#Phillips1977|Phillips (1977)]], page 43.</ref>
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