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    Re: DR thread from Nov-Dec '04
    From: George Huxtable
    Date: 2005 Jan 19, 23:35 +0000

    Jared Sherman wrote-
    >The longer the wind has been blowing, and the longer the fetch is, the
    >stronger the impact on the water will be.
    My comment:
    Well, that's undoubtedly true as far as fetch and waves are concerned, but
    I've seen no evidence that it's the case for wind-drift, which is what we
    were talking about. Jared avoided committing himself on that point by using
    the equivocal word "impact".
    I can see no reason why wind-drift shouldn't apply to a village duck-pond,
    though suitably modified to account for its shallowness. I can't call to
    mind any body of research on village duckponds, however. In my younger days
    I used to race a dinghy on a reservoir, and we were always conscious (or
    perhaps just THOUGHT we were conscious) of some wind-driven surface current
    on a windy day.
    Because wind-drift is a rather local circulation, being balanced, in the
    oceans, by a return counter-current a few hundred feet below, there's no
    call for energy-transfer over thousands of miles, as there is for the
    buildup of wave energy.
    Jared's other point, about drift depending on how long the wind blows,
    seems more valid. It must take time for the friction of wind at the surface
    to transfer energy to the surface current. If the wind were suddenly
    switched off, how long would it take for the ocean wind-currents to come to
    rest? Hours? Days? Weeks? Your guess is as good as mine. Perhaps there's a
    time-lag to be seen between the global wind circulation patterns and the
    corresponding ocean currents, at times such as the monsoons.
    contact George Huxtable by email at george@huxtable.u-net.com, by phone at
    01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy
    Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.

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