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    Re: Havnetid/hamntid
    From: Frank Reed
    Date: 2016 Oct 8, 11:02 -0700

    Yes, it's called the "establishment" of the tide (or port), but most people consider this a case where English does not have a common word, or has lost a common word for this property of the tides, and this word "establishment" has been supposedly been borrowed from the French in technical works on tides. It's a rather ugly word which provides no hint whatsoever of its meaning and one which could be ditched in a month if some other word caught on somehow.

    From a mathematical point of view, there are different "establishments" for the principal lunar and solar diurnal components of the tide. The lunar high tide might occur two hours after meridian transit of the Moon, for example, while the solar high tide might occur three hours after meridian transit of the Sun. These delays are equivalent mathematically to the phase lags of driven oscillators which can vary significantly for slightly different drivining frequencies. And since they have different "establishments" or phase lags, they do not match up when the positions of the Sun and Moon match up in the sky. This is the origin of the lag in the Spring tides, which by a naive model should occur exactly at New Moon and Full Moon, but in practice, thanks to this difference in the two phase lags, occur a day or two (or more) after the "syzygy". This is real, by the way. Spring tides do not occur at New Moon and Full Moon. In most locations they occur one to three days later.

    Frank Reed
    Conanicut Island USA

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