High tides and low tides

[geordief]

I operate as a rule of thumb  that the time of high tide advances by about an hour from one day to the next.

Not exactly of course -a bit under the hour I think .

I don't understand ,though why  these time differences are irregular.

 

One day it might be around and hour and the next day it could  be about 45 minutes.

 

What causes this irregular pattern?

 

Are the tides are part of a  chaotic global maritime weather system?

[MigL]

If the Earth was a perfect sphere, and evenly covered in water, I suspect tides would be almost like clockwork.
IRL, tides are affected by geography, and water takes time to flow in and out of the 'nooks and crannies' that make up coastlines.

I would think ,,,

[studiot]

2 hours ago, geordief said:

I operate as a rule of thumb  that the time of high tide advances by about an hour from one day to the next.

Not exactly of course -a bit under the hour I think .

I don't understand ,though why  these time differences are irregular.

 

One day it might be around and hour and the next day it could  be about 45 minutes.

 

What causes this irregular pattern?

 

Are the tides are part of a  chaotic global maritime weather system?

The shape of the Moon's orbit is an ellipse with the Earth at one focus.

So the actual Earth - Moon distance varies over that orbit by about 13%.

https://oceanservice.noaa.gov/education/tutorial_tides/tides06_variations.html

[MigL]

I was only looking at one aspect of the problem, the Earth, and totally ignoring the other factor, the moon, in this problem, Studiot.
Thanks for always thinking clearly.

Just to expand my consideration even further, would the constructive/destructive interference of the much smaller solar tides, with their yearly ( as opposed to the moon's monthly ) cycle, also have some effect ?
( I hope that's not mentioned in your link or I'll look real foolish, as I haven't read it yet )
 

[studiot]

1 hour ago, MigL said:

I was only looking at one aspect of the problem, the Earth, and totally ignoring the other factor, the moon, in this problem, Studiot.
Thanks for always thinking clearly.

Just to expand my consideration even further, would the constructive/destructive interference of the much smaller solar tides, with their yearly ( as opposed to the moon's monthly ) cycle, also have some effect ?
( I hope that's not mentioned in your link or I'll look real foolish, as I haven't read it yet )
 

Yes I think there is a small solar component but I haven't done any harmonic analysis of tides since the 1970s.

But the result of the elliptical orbits of both the Earth rond the Sun and the Moon around the Earth is that the 'passing velocity' varies as the bodies go round.
Kepler's laws say equal areas swept out in equal times. Not constant cvelocity around the ellipse.

The 'equilibrium tide' therefore is not driven by a constant passing velocity gravitational pull.

However you are quite right to observe that local topography has a great influence on the actual wave that is observed at any tidal station.
Waters partly enclosed by land are subject to resonance and standing wave effects, just as the water surface in a bathtub laps back and fore.
Southampton (the Solent) for instance has a 'double maximum'  and the North Sea slops around just like the bathwater.

[geordief]

16 hours ago, studiot said:

The shape of the Moon's orbit is an ellipse with the Earth at one focus.

So the actual Earth - Moon distance varies over that orbit by about 13%.

https://oceanservice.noaa.gov/education/tutorial_tides/tides06_variations.html

So the irregularity  in the day to day advances in the times of the high tides would be down to the local topography?

Otherwise ,if it was just the supposition of the lunar and solar  effects  it would seem to me that the  changes would be smoother

I can still discern a pattern in the irregularity where I am in that the time interval between the  high tides seem to alternate between  a greater and a smaller amount (although the exact numbers do not repeat)

 

But that would presumably  be a different  pattern in different  areas

 

[studiot]

39 minutes ago, geordief said:

So the irregularity  in the day to day advances in the times of the high tides would be down to the local topography?

Otherwise ,if it was just the supposition of the lunar and solar  effects  it would seem to me that the  changes would be smoother

I can still discern a pattern in the irregularity where I am in that the time interval between the  high tides seem to alternate between  a greater and a smaller amount (although the exact numbers do not repeat)

 

But that would presumably  be a different  pattern in different  areas

 

That's not what I said.

There are seven variables involved.

Four of these are the independent driving and controlling factors and three are the dependent variables describing the results.

The three resultant or dependent variables are

1) The max and min heights of the tides at any particular location and day.

2) The shape of the wave peaks and troughs, plotted as tide height against time at any particular location.

3) The timing of these peaks and troughs at any one location. (That is the relationahip of the timing from one peak to the next and its variation, which is what you are asking about.)

 

The independent driving variables are

A) The gravitational pull of the Moon.

B) The gravitational pull of the Sun.

The independent modifying and controlling variables are

C) The local topography.

D) Meteorological modifications.  That is changes to any or all of the above dependent variables due to the local weather. These vary from day to day and are not cyclic.

 

The Moon's gravitational pull causes a bulge in the water surface that is dragged round the Earth as the Moon orbits.

As MIgL has already said if the Earth was a perfect smooth spherical water world this would result in a 'clockwork tide'. The height of this bulge above the mean level would be high water and travel round the earth at a regular daily rate.

However this height is modified by the interaction of the Sun's gravity which results in a periodic monthly variation of this height called 'spring and neap' tides.

But the story does not quite end there because the lunar orbital month is just a little bit shorter than the solar month, which means that the timing of the the interaction varies as the Earth-Moon system travels around the Sun. In other words the the Moon does not make a whole number of orbits of the Earth in the time it takes for the Earht to orbit the Sun.

This basic pattern is called 'the equilibrium tide' and is nearly sinusoidal in shape.

But the equilibrium tides faces two additional 'controllong' factors.

The local topography is neither smooth nor part of a perfect sphere and varies in depth.

This changes the general nearly sinusoidal shape to a more irregular pattern. But any modification to the timing is repeated daily as the topography does not change from day to day.

It does not induce the cyclic day by day slippage of the high tide around the clock over about a fortnight, that is generated by the phasing difference between the Moon's orbit and that of the Earth.
 

Finally, the weather (mostly wind) can hold back or push forward the timing of high tide by quite a few minutes and also hold its height down or pile it up.
This is a random day to day affair that has no cyclicity.