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    Re: Wind drift, was: DR thread from Nov-Dec '04
    From: Trevor Kenchington
    Date: 2005 Jan 24, 09:18 -0400

    You wrote:
    > Bill-
    > <<4.  By your definition of seiche, when the wind decreases/stops, gravity
    > once again prevails and the piled up water on the leeward side of the body
    > rushes to the former windward end to establish equilibrium (level off),
    > setting up a wave.
    > 5.  If the basin is sympathetic, this "sloshing" may be rather dramatic for
    > a tideless body of water.>>
    > Do you recall the recent reports of the tsunami, where the ocean rose, then
    > fell, then rose again?
    Invoking tsunamis really doesn't help. Those are progressive waves,
    whereas seiches are standing waves.
    > I suspect what the Annapolis Book is saying may be
    > called seiches in lakes, is not the current itself, but the repeated
    > sloshing of waves back and forth across the body of water, after the wind
    > falls or as it lulls. Once the water piled up "over here" is no longer being
    > wind driven, it will go "back there" and on reaching the opposite shore, it
    > will reflect back and forth again and again, many times, until the water has
    > expended the energy from all that wind.
    A point already made on this thread.
    > If the motion and the basin were
    > resonant, that would match the definition of seiche as I'd heard it.
    A point already refuted on this thread.
    Once the wind force is removed, the water is only subject to gravity and
    the natural period of the lake. That is: _All_ seiche motion is at the
    resonant frequency of the basin concerned.
    > Why
    > they'd associate a *current* with that...dunno.
    Perhaps because moving all of that water from one end of a lake to the
    other requires a current to flow? If you are near the node, around the
    middle of the length of the lake, all you will experience of a seiche is
    the horizontal movement of the water.
    But more likely because the editors of the textbook have got themselves
    quite confused between the effects of the wind driving water down the
    lake and the subsequent seiche which eventually restores a level surface.
    Trevor Kenchington
    Trevor J. Kenchington PhD                         Gadus@iStar.ca
    Gadus Associates,                                 Office(902) 889-9250
    R.R.#1, Musquodoboit Harbour,                     Fax   (902) 889-9251
    Nova Scotia  B0J 2L0, CANADA                      Home  (902) 889-3555
                         Science Serving the Fisheries

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