Talk:Tide/Archive 2

Assessment comment
Substituted at 08:44, 30 April 2016 (UTC)

The Schematic Drawing
This widely used drawing is misleading. It implies that the mid-ocean high tide (away from the influence of continental shorelines) should occur when the moon is overhead. This would be true only if the moon were in geostationary orbit, in fixed position over a single meridian of longitude. Since the earth rotates 28 times faster than the moon orbits, the tides are about 45 degrees out of phase with the sublunar and antipodal positions.

When I lived in Honolulu, I noticed that high tide came about three hours after the moon passed overhead, or underfoot. Even though the maximum lifting force comes when the moon is overhead, or underfoot, water is heavy, and tidal currents have momentum. At a given meridian, water continues to pile up after the moon has passed on (actually, after the earth has rotated that location out from under the moon). This distinction is important, because it explains why the moon is slowly getting farther away.

Since the high-tide bulge of open-ocean water is always about 45 degrees of longitude east of the sublunar position, it tends to pull the moon forward, thereby raising it into a higher orbit.

The oversimplified diagram may be easier to understand, but it is wrong enough to cause confusion. I suggest a modification.



HowardMorland (talk) 08:54, 30 October 2016 (UTC)


 * You're right that the drawing is misleading. It, or an approximation to it, would only work if the planet had no appreciable land masses - a sort of Waterworld.  Consider the "bulge" sweeping across the Pacific: how does it jump to the Atlantic without climbing the Rockies and Andes?  A couple of hours later the tides will have to vault over the Eurasia/Africa landmass!
 * The lifting force is tiny (from memory a few cm). What is more significant is the tractive force which derives from the differential gravity.  This starts up oscillations which can either appear as E-W "sloshes" (the bathwater effect) or more commonly as large rotary systems.  In the Pacific there are around 6 "amphidromic points" or centers of the rotary systems: see the M2 map in the Physics section.  Judging by eye, Hawaii is in an interesting position being on the junction of the influences of the north Pacific and the Tahiti systems.  One tidal bulge will sweep southwards due to the system centered to the east, another westwards due to that in  the south.  What the combined tidal pattern will be is far to complex for such a simple map and analysis.
 * It actually gets a lot more complex than this though, there are many smaller systems superimposed upon the M2 system depending upon the shape and bottom profile of the basins. Martin of Sheffield (talk) 11:59, 30 October 2016 (UTC)


 * I see from sources in the above discussion that the tidal bulge supposedly lags the sublunar longitude meridian by only 3 degrees, or 12 minutes time, not 45 degrees and 3 hours as my diagram depicts (and as I have observed anecdotally). I gather the small 3 degree lag is, in fact, what drives the moon into an ever higher orbit, getting farther away at the rate of fingernail growth.


 * However, if there is anywhere on earth where this 3 degree lag can be observed, a tropical island in the mid-Pacific, like Wake Island, should be the place. I am mystified as to why the tidal bulge arrives at Wake Island 3 hours late. We know it travels at over 1000 miles per hour, to keep pace with the moon at the equator, and that the actual movement of water toward the sublunar meridian, which causes the water to pile up into the tidal bulge, is not very fast in the open ocean.  The inertia explanation for a significant time lag seems to make intuitive sense.


 * I have found global color-coded contour maps showing the tidal amplitude around the world. Has anybody made such a map for time lag between the sublunar meridian and the tidal bulge?  It would be helpful.


 * There are many conflicting explanations about how the tides work -- and lots of people explaining how every theory but their own is incorrect. The Wikipedia policy of requiring citations breaks down here, because every theory comes with ample citations, from articles, textbooks, and the like. HowardMorland (talk) 02:54, 31 October 2016 (UTC)


 * See the pages leading up to and following for a start.  The first paragraph of  points out the continental problem for the simple twin bulge model, it's from NOAA, the official US maritime agency.  The page  is the entry point to NOAA information about tides.   shows how NOAA predicts tides for Hawaii, you'll notice that the predictions are either "weak and variable" or else "harmonic".  Harmonic analysis is derived from an understanding of the tractor effect and the large rotary systems (see works by Doodson and others, particularly [if you can get a copy] the UK Admiralty's handbook of tides).  Page  lists the components for Honolulu.  You'll notice how complex they are.  Tide-predicting machine is also worth a quick read, you'll see again that it is driven by an understanding of harmonic constants, not a simple bulge model.
 * So, the answer to your question about why "the tidal bulge supposedly lags the sublunar longitude meridian" is that it doesn't. The oscillations are excited by lunar and solar gravitation but are not the simple twin bulges racing round the world.  I urge you to look again at the M2 map in the article, it is the replacement for "a map for time lag between the sublunar meridian and the tidal bulge" reflecting the complete model. Martin of Sheffield (talk) 10:16, 31 October 2016 (UTC)

Tides and latitudes
Why is the tidal amplitude greater in the higher latitudes than at the equator? 65.166.78.66 14:38, 6 March 2005‎ (UTC)


 * Is it? Probably because the Moon's orbit is inclined with respect to Earth's equator. You'll probably find the equinoctial tides (when Sun and possibly Moon are in Earth's equatorial plane) are highest at the equator.
 * Urhixidur 15:37, 2005 Mar 6 (UTC)


 * Clearly the forces causing tides are biggest at points on the line through the earth's and moon's centres. So the hight can also be expected to be more. Since the moon's orbit is practically in the ecliptic, the forces are highest between the tropics. &minus;Woodstone 19:02, 2005 Mar 6 (UTC)


 * It may look like the tidal amplitude is greater in regions in the higher latitudes of the earth but there's no causal relation between the two.
 * The inclination of the moon's orbit to the ecliptic is slightly over 5°. Depending on the position of the moon's nodes, the inclination of the moon to the earth's equator (and the maximum tidal force) is at some point between 28.5°N and 28.5°S when the ascending node of the moon's orbit coincides with the vernal equinox (like it will do at about the summer solstice of june 2006; you'll notice at that time that at the days around new moon, the moon wil be very high above the horizon round midday). The inclination of the moon to the earth's equator (and the maximum tidal force) will be at some point between 18.5°N and 18.5°S when the ascending node of the moon's orbit coincides with the autumnal equinox (like it will do in about 9.3 years after june 2006). This is what is often called the 18.6 year cycle of the moon's orbit. You'll have noticed that the maximum inclination of the moon to the earth's equator varies from 18.5° (N or S) to 28.5° (N or S) over time.
 * The maximum tidal force due to the moon's gravitation will be between these boundaries. At present the maximum tidal force due to the moon will be between 28.5° N and 28.5° S. In about 9.3 years the maximum tidal force will be between the boundaries of 18.5° N and 18.5° S. But the actual tidal amplitude depends on many more factors than just the tidal force. Most important is the depth of the ocean basin. If a tidal wave travels from deep water into a shalow basin, the wave is slowed down but the amplitude increases. Also if the wave travels into a funnel shaped basin (like the English Channel or the Bay of Fundy) the amplitude increases much. It's only a coincidence that sea basins that fulfill such conditions are found in the higher latitudes. To think that the tidal amplitude is only a function of tidal force would be an enormous simplification of this quite complicated fenomenon. Wikiklaas 23:32, 13 March 2006 (UTC)

Amplitudes do not follow a definite pattern with latitude. For example the semi-diurnal range in the Gulf of Carpentaria is some 8m. Long period tides Mf and Mm do show a lat dependency, though. The analytic solution by Kelvin is larger at greater lats. The cutoff lat for M2 is 71N/S, as the inertial period (half pendulum day) is shorter than the tidal frequency. Mf and Mm can exist at such low frequencies since they are mixture of long and short Rossby waves (Wunsch et al, Progr Oceanogr, 1997). — Preceding unsigned comment added by 27.33.243.64 (talk) 10:30, 14 December 2015 (UTC)

Tidal forces are extremely small, typically a millionth of a newton and cannot 'lift' the water significantly. The effect is strongest at the periphery of a spherical cap centered on the Moon's nadir point, where the force is horizontal, causing the water there tp flow toward the nadir point from all azimuths. This is why the effects are stronger at higher latitudes. Angiras — Preceding unsigned comment added by 2601:704:0:9010:2D50:1613:CE78:53C (talk) 03:08, 4 October 2017 (UTC)

Basic Physics of all Tides
The article is quite poor, IMHO. No mention is made of the ocean's internal tides, ie as in Marsigli's principle (1681). The earth tides are barely discussed, and Mm and Mf and the 18.6yr cycle are not mentioned at all. A better ref to the solid earth tides is required, and I suspect the quoted amplitudes are a bit too small. Cartright's crustal loading has not been mentioned. It reduces the ocean's external amplitudes by 15%; an interaction between the ocean and solid earth.

No mention has been made of the closely related lunar nutation. The moon should have tides, like the earth, but since it does not have a liquid mantle it cannot deform without an excessive loss of KE. It is why the moon stopped rotating, and now one side of the moon always faces the earth. This was not discovered until 1960, by Munk and McDonald. The moon's KE of rotation was lost to internal tidal friction, while the total system momentum was conserved by the mood moving further away from the earth.

Since astronomical nodal frequencies are very precise and stable (well the important ones are) the tidal initial-value problem may be reduced to an elliptical boundary-value problem, by separation of variables. This implies that (assuming linearity) that the u and v components of velocity form a tidal vector ellipse. u=Ucos(omega*t-p1) and v=Vsin(omega*t-p1). This always traces an ellipse with eccentricity U/V and the major axis aligned along p1. Near boundaries one of U or V will be very small, and the flow is back and forth along a line. Away from boundaries, the Coriolis will cause the flow rotation to be clockwise in NH, and opposite in SH. Tidal vectors are usually quoted this way. (If non-linearity is to be included, such as modelling a storm surge at a flood tide, then it must be solved as an IV problem.) Heights are quoted by amp and phase, relative to UTC.

Laplace's great achievement of the cutoff latitude of the diurnal tides at the critical lat is not mentioned. All tides with periods shorter than a half pendulum day (12hrs/sin(lat)) are Poincare waves. Inertial oscillations in fact do have small height range due to Beta (the LTE solution is on an f-plane). All tides with longer periods than the inertial period must be planetary (Rossby) waves; Wunsch et al, progr oceanogr, 1997. This 1997 paper was the last "great leap forward" in the understanding of the tides.

The polar tide is not caused by planetary forcing. It's period is not fixed, and it causes the erratic Chandler wobble. It is believed to be the swapping of momentum between ocean and earth. There is also an equatorial tide in the Pacific of 3-days duration. It does not correspond to any astronomic nodal frequency.27.33.243.64 (talk) 23:48, 14 December 2015 (UTC)

The article could help clarify a widespread confusion - thus pointing out that centrifugal forces aren't involved in tides. Such forces apply to rotating objects and not to revolving ones. Tides would exist even if the Moon wasn't revolving around the Earth, but was in free fall instead. — Preceding unsigned comment added by 137.75.200.138 (talk) 18:05, 15 March 2018 (UTC)

External links modified (January 2018)
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WP:EASTEREGG
Hi guys. I've noticed a fair number of editors tend to forget about WP:EASTEREGG, and will often undo edits that repair articles with piped-link errors. If you're having trouble seeing the reasoning for this type of edit, it could be good to brush up on WP:EASTEREGG. InternetMeme (talk)
 * They are not errors. The very first guideline for when to use piped links is to use them when:
 * the wording of the exact link title does not fit in context
 * which is the case here. It’s the case in many technical fields, that the common properties of a subject, such as the times and sizes, have particular articles for that subject. We want to link to those articles. But in this context, to not scare readers with overly technical language in the lead we want to describe them in ways they will be familiar with. So the text says "the times ... of tides", but the link goes to tide table which describe how tide times are recorded.-- JohnBlackburne wordsdeeds 22:58, 25 March 2018 (UTC)
 * That's not what piped links are for: They're never used for translation of technical terms. If you want to use a technical term with a lay explanatory term, brackets are what you want.
 * What you're describing is a poster child example of WP:EASTEREGG: There's no way any normal person could guess that "timescales" would link to "Lunitidal interval". That's a complete Easter Egg.
 * Perhaps you could read WP:EASTEREGG again, just to make sure you can see why it's a problem.
 * InternetMeme (talk) 14:36, 26 March 2018 (UTC)

Move discussion in progress
There is a move discussion in progress on Talk:Ebb tide (disambiguation) which affects this page. Please participate on that page and not in this talk page section. Thank you. —RMCD bot 01:04, 2 May 2018 (UTC)

M4 needs an explanation
The M4 constituent of the tide appears suddenly in the "Timing" section, which says, without explanation, "Southampton in the United Kingdom has a double high water caused by the interaction between the M2 and M4 tidal constituents." The M2 constituent has been introduced (it is the twice-daily forcing due to the Moon). But what is the M4 constituent? There is a reference but it is not open access so it does not help. Perhaps the article previously had an explanation but it was removed. Wikipedia also has a table of constituents at Earth tide but this does not include M4. One has to go all the way to Theory of tides to find a description. Gdr 19:09, 21 May 2018 (UTC)


 * The most important tidal factors are due to the Sun and the Moon. They are symbolised by S and M respectively.  The subscripts represent the approximate period.  For long periods these are a annual, m (lunar) monthly, f fortnightly.  For cycles of a day or less the subscript is a number indicating approximately the number of cycles per day, so the solar diurnal (daily) tide is S1 and the lunar semi-diurnal (half daily) tide is M2.  Where tides run over shallows the wave form starts to distort (roughly speaking the crests start to catch up with the troughs, watch waves approaching a shelving beach before they break for example).  Applying a harmonic analysis of the wave yields terms in a quarter day (M4), sixth (M6) and higher.  The higher the term the smaller it is and so the less important.  Around Southampton there is a substantial area of shallow water (the Solent), and the M4 term becomes important.  I don't have the details to hand, but it finds a 6 hr-resonance in the area, and so is sustained and added to the M2 main tide.  An analogy of this is the observed difference between morning and evening tides, particularly at springs.  In this analogy it is the S1 affecting the M2 (the influence of S2 being to create springs and neaps).
 * Returning to the M4/M2 interactions. M4 oscillations occur over a smaller area than the larger, slower M2 changes.  To the west of Southampton lies Portland and there the M4 is roughly in phase with Southampton whilst the M2 is out of phase.  The effect is that Portland experiences a double low water. Martin of Sheffield (talk) 20:58, 21 May 2018 (UTC)

Lowest astronomical tide says "Modern charts use this as the chart datum"
Seems incomplete to say "Modern charts use this as the chart datum". NOAA charts use MLLW Mean lower low water, the average height of the lowest tide recorded. Might be good to put a link to the Chart datum article.

Opening sentence
I tried to add "Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon and the Sun, the free fall of the Earth towards these objects, and the rotation of Earth.", but it was reverted. I changed it back, with the justification that the former version read: "Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon and the Sun and the rotation of Earth." The latter is imprecise: The tidal force does not equal the gravitational force of other celestial objects, as the article already made clear in the Physics chapter before my edits, but rather the difference in gravitational force at a particular location (e.g. at the ocean surface) in relation to the gravitational force exerted on the Earth as a whole. I think the simplest explanation of this is to include the concept of free fall in the lede. Narssarssuaq (talk) 23:08, 13 August 2018 (UTC)

Missing information
I had to search google to find out where Alma, New Brunswick is. Well it is in Canada. Can you add it to the two images on the top? רם אזרח מזרחי (talk) 18:48, 26 August 2018 (UTC)


 * ✅. Not really necessary, as hovering over the existing links immediately shows Canada... but done anyway: . - DVdm (talk) 18:58, 26 August 2018 (UTC)

COOK STRAIT
Concerning the text and diagram of tides in Cook Strait, Nelson is on the southern side, Wellington on the north ✅ Martin of Sheffield (talk) 09:57, 30 July 2019 (UTC)

Cook Strait ... again
The description belonging to the diagram was corrected, but the main body of text still has Nelson to the north and Wellington to the south. It is the other way around.
 * ✅ Since you can edit here, you can edit in mainspace and could therefore have done the corrections yourself. Martin of Sheffield (talk) 21:28, 3 August 2019 (UTC)

Cook Strait ... again ... again
There are still errors in the text saying Nelson is north and Wellington is south. I am not a registered Wikipedia user, and as a matter of principle I do not register with internet websites. I cannot therefore edit the text myself. Regards Alan Graham Robinson
 * You do not have to register with WP to edit, so you can edit yourself. I couldn't see where the problem is, so unless you make it clear (not just airy "There are still errors") any errors will go uncorrected.  Please ensure you sign all edits on the talk page with four tildes ( ~ ). Martin of Sheffield (talk) 22:27, 4 August 2019 (UTC)

When I open the page for editing I see this ... 'This page is currently semi-protected so that only established, registered users can edit it.' But seeing how you turn personal (not just an airy) might I just make this observation; I thought Wikipedia existed for the betterment of mankind by the dissipation of knowledge and fact. I should have thought that the Wikipedia community were keen to raise standards and enhance Wikipedia's reputation. I should have thought that whoever put these mistakes in the article would have welcomed them being pointed out. I should have thought that people participating in this talk page would have their facts straight before becoming huffy with those who come here, with the best intentions, to make improvements. But in retrospect, maybe I should have read the Wikipedia article on ego before made such assumptions.

Anyway, seeing how you haven't read the article carefully and for your guidance, as I read the article this morning it says ' only one of the two spring tides at the north end (Nelson) has a counterpart spring tide at the south end (Wellington), so the resulting behaviour follows neither reference harbour.' And if we really want to be fussy, Wellington is in fact on the EAST side of Cook Strait, situated on NORTH Island. Nelson isn't on Cook Strait at all, but on South Island and some 100 km to the WEST of Cook Strait. I am not a registered user and therefore cannot correct this tripe.85.80.224.22 (talk) 04:49, 5 August 2019 (UTC) Alan Graham Robinson
 * Right, first an apology. I hadn't seen that the article was one of the few that has had to be semi-protected.  Basically this means there has been a lot of vandalism in the past and the normal rules have had to be suspended to stop the vandals.
 * I'm not too familiar with NZ geography (we did in at school in 1966/7), so do tend to check things up before making changes. The Cook strait runs roughly NW to SE, and Wellington is at the SE according to Bing maps.  There does appear to be a Nelson in the middle of the Cook straight, see Nelson, New Zealand.  By the way, the article mentions Napier, but the only Napier I  have found is Napier, New Zealand which certainly is not on the Cook Strait, but is on the East side of North Island, and so I assume it only gets one cycle of springs/neaps per month.  I've amended "south end" to be "south east end" and "north (Nelson)" to "north west end of the strait near Nelson".  Is this satisfactory?
 * Moving on, please have a read of Request edit. Whilst you don't have to use the template, the page does give guidance at point 3 as to what information is needed.  Please remember that editors are volunteers who are interested in particular topics and points that are important in themselves may be peripheral to the particular page.  That's why we need a collaboration bringing in this case your knowledge of NZ to my interest in tides. BTW, thanks for using the signature mechanism. Martin of Sheffield (talk) 12:02, 5 August 2019 (UTC)

Metric Consistency
I don't mind the use of either English or Metric systems, but we should be consistent in each article (as we do with BE and AE, Serial Commas, etc).

In the section Lake Tides, the first measurement is in metric, converted to English parenthetically. The next sentence has English, converted to metric...followed by a FRACTIONAL measurement instead of decimal. I would make the changes myself, but I'm not certain which way to go.

Thanks, WesT (talk) 18:20, 14 August 2019 (UTC)


 * ✅ as best as I can; kept the fraction since that's what's given in the source and I'm hesitant to convert to a decimal giving a false sense of measurement precision; units are now given in metric-first. –Deacon Vorbis (carbon &bull; videos) 03:39, 15 August 2019 (UTC)


 * Thanks! That's what I would have opted for, but I wasn't bold enough to try. WesT (talk) 17:09, 19 August 2019 (UTC)

Origin of the recognition of tidal physics in India
Hi, I'm not aware of every reference to the effects of the diurnal cycle on the tides in Indian literature/sciences, however it should be noted that the Ramayana, the ancient Indian epic, in the section Sundara Kanda talks of this effect and perhaps deserves a note in the "History of tides" section. http://www.hindupedia.com/en/Sundara_Kanda This section narrates Hanuman, one of the characters, observing the moon.

"Then he saw the moon, which destroys the sorrows of the world, which increased the levels of the great sea and which traveled by giving light to all beings."

Wrong explanation and opposite effect?
I've read before that the moon and sun do not attract the water like it says here (sorry, can't find the article). The moon and sun actually attract the earth, that is not solid, so the water flows down in the other direction, making the tides. I just checked the tide and moon positions for my city and it's consistent. I'm in Quebec City, the full moon was on the horizon around 6am (May 7th 2020), and it was a high tide, and at 2pm the moon will be at nadir (down) and the sun up, making a low tide (I checked the moon position with the SkyMap app and the tides here: www.tide-forecast.com/locations/Quebec-City-Quebec/tides/latest). I googled a bit and it seems that most webpages are consistent with wikipedia, but it's not what I just observed when looking at the actual data. Someone care to tell me if I'm disastrously wrong? Thanks! Ccvieira (talk) 13:51, 7 May 2020 (UTC)
 * Here we can only discuss the article, not its subject — see wp:Talk page guidelines. You can try asking at our wp:Reference desk/Science. Good luck. - DVdm (talk) 14:15, 7 May 2020 (UTC)
 * The section on tidal physics explains that the driving force is the differing lunar (and to a lesser extent solar) gravitational force over the Earth's surface. This produces a oscillating tractive force that operates on ocean basins (see bathymetry) to sustain resonant patterns of movement.  The timing of high water at any given point is dependent upon the movement of masses of water around an amphidromic point.  As the mass sweeps past there is high tide, when the mass is missing there is low tide.  I'm sorry to say that on both points you make you are wrong, possibly not disastrously though :-).  If you need more help, look for books designed for sailors, not schoolkids, or as  says take this to the reference desk. Martin of Sheffield (talk) 15:14, 7 May 2020 (UTC)
 * Gravity and inertia affect all matter with mass. Solid or liquid does not matter, except that liquid flows, solid not so much. &middot; &middot; &middot; Peter Southwood (talk): 15:43, 24 August 2020 (UTC)


 * Ref desk discussion: WP:Reference desk/Science. -- ToE 22:47, 9 May 2020 (UTC)


 * I figure this article is, in large part, designed for future physicists and oceanographers, who are splendid people but not ones who most need to look up tides in a general encyclopedia. Jim.henderson (talk) 18:00, 12 May 2020 (UTC)

Please look again at the explanation
I am a professional engineer with a scientific (Physics) education. I visited this site in the hope of finding an explanation for the two opposite tidal bulges, but found that the explanation given ('Forces' section) was completely impenetrable. God knows what a layman would make of it. I have gone away no better informed that I started. PLEASE try again to give an explanation which is to the point, and which can be followed by an intelligent reader. We want to know why the oceans rise on opposite sides of the earth. — Preceding unsigned comment added by 92.238.4.160 (talk • contribs) 07:00, 28 June 2020 (UTC)
 * The short answer is that there aren't – that is the schoolbook explanation. Even the Venerable Bede in AD 725 realised that the water was surging around the sea: he explains that the tide "deserts these shores in order to be able all the more to be able to flood other [shores] when it arrives there".  Consider for a moment if there were simply two bulges chasing around the planet.  As the bulge sweeps across the Pacific it encounters the Americas and must either stream past Cape Horn at an incredible velocity, or simply jump over the whole continents.  Three hours later it hits Europe and Africa so has to find its way around the Cape of Good Hope at hypersonic speed or else jump the whole of Europe and Asia.  Perhaps that's why the British Isles get a lot of rain? :-)  Where you are correct is that a rewrite is needed.  I suspect that there is a lot of timidity here, attempting to debunk the two bulge analysis always results in shouts from those who learnt it at school and know that it's right, even when they can see it is wrong. Martin of Sheffield (talk) 09:18, 28 June 2020 (UTC)
 * More a sloshing around in the basins, I would have said. Gravitational/centrifugal effects each give the water a bit of a kick as they move through on their schedule, and the water in a basin sloshes according to how well the water in each basin resonates to each influence. Seeing these combinations in action is quite an experience for someone who has lived with basically mild M2+S2 all their life.&middot; &middot; &middot; Peter Southwood (talk): 15:28, 24 August 2020 (UTC)
 * That's a pretty good qualitative description, far better than the two bulge water world approach. It can be quite amusing seeing the surprise on trainees from the Mediterranean (a foot or two tides only) being confronted with tides of 3m (10') neaps and 6m (20') springs!  Then they discover the tidal stream is over 2kts at springs in the river which for a 6kt boat is the difference between under 4kts to over 8kts. :-)  Martin of Sheffield (talk) 15:56, 24 August 2020 (UTC)
 * IMO there would be nothing wrong with the "two bulge" picture if you change the caption to call it an illustration of the forcing function that causes the water to slosh about in the world's tidal basins. A link to this video, or a recreation of what the video shows would illustrate how the water sloshes about in response to that forcing function. 74.111.99.101 (talk) 17:38, 24 October 2020 (UTC)

Six components in graph, only two mentioned in text
In the figure showing components of the tide, there are 6 waves. M2 = lunar semidiurnal, S2 = solar semidiurnal, so far good. Then N2 = what? another semidiurnal? but from what influence? and K1, O1 and P1, presumably diurnal, but caused by what? Cheers, &middot; &middot; &middot; Peter Southwood (talk): 15:16, 24 August 2020 (UTC)
 * I've provided a wikilink to Theory of tides which should help. Martin of Sheffield (talk) 21:42, 24 August 2020 (UTC)