Comments on: Amphidromic Points: tidal spiders in a real World

By: STREEL

STREEL — Mon, 24 Aug 2020 09:55:56 +0000

Hello, is-it possible to receive the legend of Global distribution of amphidromic points with their cotidal lines and relative coranges ?

By: Clay Dumke

Clay Dumke — Tue, 05 May 2020 17:54:12 +0000

Hello,
Not sure I’ll get a reply as this post was entered a few years ago… The Gulfstream moves through the Atlantic in a ‘clock wise’ flow versus the tides circles going anticlockwise. Can you discuss any associations or correlations that may exist between these opposing forces?

By: James Balkwill

James Balkwill — Sat, 24 Aug 2019 07:08:22 +0000

Very good explanation but I am confused about one thing. The should be two waves originally,one gravitational and one centripeatal. Othrperwise the will only be one high tides a day and actual there are two. I can see how to get this because the superposition of two in the first diagram gives a total tidal that s flat. I think it must be caused by progressive waves that combine to spake a standing wave but can’t see how. Can you help !

By: Malcolm

Malcolm — Sun, 21 Apr 2019 11:45:30 +0000

Hi Martin VJ, How can we be certain that Sea Water is not the passive participant in daily tidal changes while the Earth’s Crust is the active participant? It seems that some of the amphidromic nodes in the North Sea are close to positive gravity anomalies e.g. off Hordaland SW Norway +40 mGal and off Great Yarmouth (52.40 N 2.40 E) +2mGal. It seems unlikely that fluid water has a memory that ‘knows’ where its amphidromic nodes are located and always respects those locations, regardless of seasonal changes and megatides.
Since GPS heights are calibrated from fixed stations nearby onshore, if the crust were the active participant, those stations would rise and fall simultaneously with observed tidal heights on the adjacent coast. An observer at the coast would see the water rise and fall without realising that the beach itself was falling and rising with respect to a fixed geoid.

By: Richard James

Richard James — Wed, 10 Apr 2019 11:01:12 +0000

I note that not all the nodes in the southern hemisphere rotate clockwise. Is that because the effect of the bigger adjacent rotations overides the coriolis effect in these smaller areas?

By: Martin VJ

Martin VJ — Sun, 12 Nov 2017 16:46:16 +0000

Edward, start with high water at the south, this will give a slope down to the north. The water wants to flow down this slope and as it does so it will be deflected to the right i.e East. When it reaches high water on the Eastern side it will want to flow down to the west, but again it will appear to be deflected to the right by the coriolis effect until high water is at the North side of the basin. When it has reached high water on the north side the slope is to the south so it is deflected to the right and high water occurs on the west side. Finally at high water on the west side the slope is to the east and the water wants to flow that way but instead gets deflected to the south. Hope that helps.

By: Martin VJ

Martin VJ — Sun, 12 Nov 2017 16:31:44 +0000

Dhanajay, the Coriolis effect applies to anything moving relative to our planet. Imagine that you throw something due east at say 30 degrees north latitude. Now you and the object thrown both had the same angular momemtum before you released it. After you released it the objects angular momemtum was greater than your angular momemtum at 30deg north. So in order to preserve its angular momemtum and it moves slightly south until it stops. Which iswhere it’s angular momemtum will eventually match that of the planet.
If you throw it in the opposite direction it will move to the north because it has less angular momemtum.

By: Catherine Bowles

Catherine Bowles — Tue, 15 Aug 2017 19:34:46 +0000

Hi. I’m wondering if you could tell me why there are several amphidromic systems in the North Sea and whether their position will be affected by storm surges. Thank you.

By: Dhananjay

Dhananjay — Wed, 19 Oct 2016 06:38:35 +0000

I have a query.When water is flowing from Europe to America and deflects rightwards (north) and when flowing from America to Europe and deflects rightwards (south) then this motion is cloclwise.
But in article it is mentioned counterclockwise.
Also does Coriolis effect deflects objects moving in East-West direction?

By: John Glasspool

John Glasspool — Mon, 25 Jan 2016 17:52:14 +0000

Fascinating! Especially as I had heard elsewhere that Tidal Nodes could be on land, and although seeming daft to laymen such as myself, I am glad you have stated it again wrt NZ.