why? Summer low-low tides near noon, winter near midnight

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carlk3
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why? Summer low-low tides near noon, winter near midnight

Post by carlk3 »

Looking at the Tidelog book and http://PlanYourDive.com, it looks like the lowest tides of the summer (for example, today's -3.1 ft) are near Noon. In the winter, the lowest-low tides seem to be near mid-night. (I looked at Seattle and for 2014 and 2013 and 2020).

I understand why the lowest low tides will be with near full or new moon, but not why they seem to depend this way on the time of day.

Thanks,
Carl
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60south
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Re: why? Summer low-low tides near noon, winter near midnigh

Post by 60south »

[Good question!] Just a guess...

It's probably related to the axial tilt of the Earth.

The northern hemisphere is tilted towards the Sun in the summer and away from it in the winter. The tilt puts us more in-line with the ecliptic (our rotational plane around the Sun) at noonish in the summer and midnight during the winter. That's when the Sun's and Moon's gravity will have the strongest influence on the tides.

If there's a physical oceanographer on the board perhaps they can confirm or recalibrate me on this. ; )
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oldsalt
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Re: why? Summer low-low tides near noon, winter near midnigh

Post by oldsalt »

60south wrote:[Good question!] Just a guess...

It's probably related to the axial tilt of the Earth.

The northern hemisphere is tilted towards the Sun in the summer and away from it in the winter. The tilt puts us more in-line with the ecliptic (our rotational plane around the Sun) at noonish in the summer and midnight during the winter. That's when the Sun's and Moon's gravity will have the strongest influence on the tides.

If there's a physical oceanographer on the board perhaps they can confirm or recalibrate me on this. ; )
You nailed it. I'm not a physical oceanographer, but I remember they covered this in one of my classes at the Naval Academy (navigation? oceanography?). The earth's inclination and the resulting seasonal effect was one of the harmonic constituents, along with the elliptical orbits of the earth about the sun and the moon about the earth (perigee/apogee, perihelion/aphelion), the earth's rotation and revolution, phases of the moon, and so on which contribute to the cyclical nature of tides. That is why tides repeat themselves every 19 years or so. Of course, this is all complicated by the geography of the tidal basins. But you've probably noticed that our greatest range of tides occur near the solstices. I am fascinated by all of this stuff.
-Curt :rawlings:
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Norris
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Re: why? Summer low-low tides near noon, winter near midnigh

Post by Norris »

Can't explain it
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