Læg også mærke til at der står beskrevet at det er ved 45 grader nordlig / sydlig breddegrad at tidevands kræfterne er størst.
Dette er naturligvis ikke rigtig, Paul! ;-)
Tidevandet skyldes mest månens tiltrækningskraft og noget solens (ca 46 procent af månens tiltrækning). Det betyder at tidevandsbølgen ude på det store dybe hav er størst under månens bane som varierer mellem ca 28 grader nord og syd. Denne tidevandsbølge kan så forstærkes lokalt, af lavbundethed (tsunamieffekt) og kontinenternes vige, odder og sunde, hvor bølgen kan vokse op til 50-100 gange størrelsen på det uforstyrrede dybe hav. De 45 grader der henvises til, skyldes altså rent lokale forhold!
Hej John!
Interessant spørgsmål som måske er mere kompliceret at svare på end som så.
Det er korrekt at månen hiver mest i vandet der og når den er nærmest jorden.
http://www.fhsu.edu/biology/Eb...html
"Tides
The gravity of the moon exerts the greatest pull on water in the oceans closest to it. The moon also pulls the Earth and pulls the oceans on the opposite side of the planet to progressively lesser degrees. Thus, bulges of high water levels are created in the oceans closest to and farthest away from moon = high tides. Depressions of low water levels are created on Earth at 90° angles to the position of the moon = low tides. The gravity of the sun also exerts gravitational pull on the water and the planet, but to a lesser degree than moon.
Generally there are 2 high tides and 2 low tides per day as the Earth rotates under the bulges and depressions, but the heights of the 2 low tides or the 2 high tides are not equal to each other. The orbital plane of the moon is not the same as the rotational plane of the earth, so the gravitational pull varies. As a result, the general sequence of the 2 high and 2 low tides during a 24-hour period is: 1) higher high tide, 2) lower low tide, 3) lower high tide, and 4) higher low tide. The lower low tides we will encounter will be early in the morning.
"Spring Tides" have nothing to do with seasons; they are the highest and lowest tides that occur when the sun and moon form a roughly straight line with the Earth. During a new moon, the sun and moon are pulling from same side. During a full moon, the sun and moon are pulling from opposite sides. "Neap Tides" (moderate tidal changes) occur when the sun and moon are at right angles to the Earth (during quarter moons).
The greatest differences in tides are during June and December, because these are when the Earth is closer to the sun during its elliptical orbit. Tides also vary with surface winds, atmospheric pressure, and other local phenomena (i.e., we want light winds and high atmospheric pressure when we visit the tidepools). Thus, tide tables offer only predicted tide levels. In the USA, tide heights are reported relative to the mean lower low tide (= 0 feet). The best low tides for viewing tidepools are below average levels (e.g., -1.6 feet).
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Hvilket også kan ses her.
http://www.youtube.com/watch?v...iDbg
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Men....
http://findarticles.com/p/arti...col1
"There are over 150 factors that can affect tide behavior along any given coast or ocean basin. The greatest influences on the tides are the Coriolis effect, landforms, and ocean depth.
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Så måske den samlede effekt er kraftigst ved 45 grader Nordlig og sydlig bredde?
Nogen der kan bidrage med mere info?
http://www.town.ststephen.nb.c...html
"The initial cause of this tidal phenomenon is the pull attraction on the worlds' oceans by the moon, sun, planets and stars. They exert their gravitational pull most in relatively narrow bands around the earth at about 45 degrees north and south latitude. This is because those are the areas tipped closest and furthest away from these celestial bodies. Although the gravitational pull on the earth by these bodies and particularly when the moon is strong, it is not enough to actually lift water but it can greatly influence its direction of the flow, thus creating ocean tides.
"
