When exactly is a spring tide?

[Midnight Drifter]

Useful' practical boat owners generally speak in terms of 'springs' being the 3 or 4 days around the biggest tides, 'neaps' being the 3 or 4 days of smallest tides and various words for the other two quarters of the fortnight.
I think anyone from Dover would call each of the 4 tides on the 26th and 27th 'a neap tide'.
Sailors I know don't generally go around arguing 'today is not spring tide , tomorrow is THE spring tide'.

Agreed. That's what I do. And anyway, as others have said, at a particular place the actual time and height of tide is affected by factors such as wind and air pressure. However, my question is not about the practicalities - it is about understanding how the timing of springs and neaps in relation to the moon's phases varies from month to month, and to do that I need to be able to say when springs and neaps occur.

 

[Midnight Drifter]

Spring/Neaps are related to amplitude, not levels of single HW or LW. A time series of amplitudes is not a continuous line, giving a local maximum/minimum which you could choose to get your istantaneous hh:mm "time" of springs, it's more like a bar chart with the bars spanning from every LW to HW to LW etc.

So, instead of thinking about the envelope of the tidal curve, I should think about a graph of tidal range. Springs occur at the maximum of this graph. To draw such a graph, the time of a particular range would have to be taken as midway between LW and HW.
My hypothesis is that, although the times of LW and HW vary from place to place, the maximum of the graph of tidal range should be at roughly the same time everywhere, and that it should be possible to produce a graph that shows the average range across the world and therefore the time of global spring tide.

 

[MontyMariner]

And anyway, as others have said, at a particular place the actual time and height of tide is affected by factors such as wind and air pressure

And that is why you can't definitely say when a maximum / minimum Spring / Neap occurs. You might calculate that it occurs 2.3485 days after the F/NM but the 'other factors' might advance or delay it by a few hours.

 

[MontyMariner]

If you want a true head scratcher, try and work out HW for Poole quay!

 

[Midnight Drifter]

And that is why you can't definitely say when a maximum / minimum Spring / Neap occurs. You might calculate that it occurs 2.3485 days after the F/NM but the 'other factors' might advance or delay it by a few hours.

The same applies to the time of HW, but the tide tables that we all use predict HW to the nearest minute. It is common for the actual tide to be different by a few minutes, but not by a few hours.

 

[B27]

Agreed. That's what I do. And anyway, as others have said, at a particular place the actual time and height of tide is affected by factors such as wind and air pressure. However, my question is not about the practicalities - it is about understanding how the timing of springs and neaps in relation to the moon's phases varies from month to month, and to do that I need to be able to say when springs and neaps occur.

If you want to disappear down some mathematical modelling rabbit hole, you would probably do better to look at the whole model of harmonic coefficients which can predict tidal height as a function of time.
Then you could have a solid, well defined frame of reference.

We talk about how 'springy' or 'neapy' the tides are, but there is no rigorous definition of 'springiness' which you could determine the peak of.

You could invent some definition of 'spring tide' such as 'when the tidal energy in the oceans of the world is at a peak' but no tow people will measure it in the same way, if you could measure it at all.

 

[B27]

If you want a true head scratcher, try and work out HW for Poole quay!

You might as well try and predict the height at Chew Valley Lake!

 

[MontyMariner]

It is common for the actual tide to be different by a few minutes, but not by a few

You would have to draw a graph of the spread of the time difference between several Springs to see what amount of time you are concerned about. It's something that has never bothered me.

 

[MontyMariner]

If you want to disappear down some mathematical modelling rabbit hole, you would probably do better to look at the whole model of harmonic coefficients which can predict tidal height as a function of time.
Then you could have a solid, well defined frame of reference.

He will need a copy of NP159 Admiralty Method of Tidal Prediction
https://www.google.com/url?sa=t&sou...QQFnoECBwQAQ&usg=AOvVaw1xk32pRTA-lc1XPKBOLKGy
PS I've also seen this https://mdnautical.com/tidal-publications/101-np-160-tidal-harmonic-constants-european-waters.html

 

[Humblebee]

Some will never be fully satiated but have a read here Types and Causes of Tidal Cycles - Tides and Water Levels: NOAA's National Ocean Service Education
and at the associated tabs (on the right) then please report back.

Interesting link, thanks.

 

[winch2]

del

 

[Roberto]

My hypothesis is that, although the times of LW and HW vary from place to place, the maximum of the graph of tidal range should be at roughly the same time everywhere, and that it should be possible to produce a graph that shows the average range across the world and therefore the time of global spring tide.

There cannot be a global spring tide across the world. There are a few different types of tides, the two extremes are semidiurnal (where the moon influence is greatest), and diurnal (where the sun influence is greatest), in between there are all sorts of mixed tides. Add to these the local fictive harmonic constants. A spring/highest amplitude tide in a semidiurnal tide area will happen when the moon influence is at its maximum; a spring tide in a diurnal tide area will happen when the sun influence is at its maximum. Moon and sun maximum influences do not happen (except very occasionally) at the same time, so spring times in the two areas will be mostly unrelated. Mixed tides will combine the two influences (plus others of course) and provide all sorts of different "spring time"

 

[B27]

There cannot be a global spring tide across the world. There are a few different types of tides, the two extremes are semidiurnal (where the moon influence is greatest), and diurnal (where the sun influence is greatest), in between there are all sorts of mixed tides. Add to these the local fictive harmonic constants. A spring/highest amplitude tide in a semidiurnal tide area will happen when the moon influence is at its maximum; a spring tide in a diurnal tide area will happen when the sun influence is at its maximum. Moon and sun maximum influences do not happen (except very occasionally) at the same time, so spring times in the two areas will be mostly unrelated. Mixed tides will combine the two influences (plus others of course) and provide all sorts of different "spring time"

Is there anywhere in the world where 'spring tides' are not close to 1 day after a full moon +/- 24 hours or so?

In as far as I've tried to understand this, full moon/new moon is when the action of Earth/Moon/Sun system is putting the most energy into tides?

So it's unlikely anywhere would be grossly different, without a very long, loss free delay line?

 

[Roberto]

Is there anywhere in the world where 'spring tides' are not close to 1 day after a full moon +/- 24 hours or so?

In as far as I've tried to understand this, full moon/new moon is when the action of Earth/Moon/Sun system is putting the most energy into tides?

So it's unlikely anywhere would be grossly different, without a very long, loss free delay line?

Interesting question out of curiosity I have drawn the graph of four primary tidal stations, Dover (semidiurnal), Galveston TX (diurnal), Rio (mixed), Muroran Japan (mixed), same dates interval, they images are aligned so hopefully moving the window side cursors one can check what happens in the various graphs at given different dates.
Say Dover springs in the middle of the image: Galveston springs seem a coupe of days later, Rio springs 4-5 days earlier, Muroran in the same cycles around those dates has very "springy" tides alterned with very "neapy" ones: are they springs or neaps?
Dover neaps (left of image) is definitely springs at Galveston, Rio neaps were about 4 days earlier, in Muroran the moon infulence is so low there is basically only one diurnal cycle (2 very near HWs) left.
The graphs cover only about 5-6 weeks, maybe stretching the charts to a longer interval (say 1year) other peculiarities might appear.