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The semiannual and 4.4-year modulations of extreme high tides

TitleThe semiannual and 4.4-year modulations of extreme high tides
Publication TypeJournal Article
Year of Publication2019
AuthorsRay R.D, Merrifield M.A
Date Published2019/08
Type of ArticleArticle
ISBN Number2169-9275
Accession NumberWOS:000490464200032
Keywordslevel; oceanography

In most places extreme high tides undergo a clear seasonal variation. It is well known that semidiurnal tides tend to peak during equinox seasons, and diurnals during solstice seasons. This is a consequence of the solar and lunar declinations, which when large maximize diurnal tides at the expense of semidiurnals. The semiannual range modulation of tidal extremes for a pure semidiurnal tide is determined mainly by the amplitude of the K-2 constituent; a pure diurnal is determined mainly by P-1. Mixed tidal regimes tend to experience maxima very roughly around the times of solstice, but not always, with the semiannual modulation generally a complicated function of constituent amplitudes and phases. These modulations are here mapped worldwide by analyzing tidal extremes predicted with a global tide model. The known 4.4-year modulation in extreme tides is a consequence of declinational and perigean effects coming in and out of phase. The phase of the 4.4-year modulation is controlled by the phase of the semiannual modulation, irrespective of whether the tide is diurnal, semidiurnal, or mixed.

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