Saturday, March 7, 2015

The amphidromic point, amphidromic systems

Good starting point - The dynamic theory of tides

1932 Bulletin of the National Research Council, Issues 77-80 (theorizes about multiple nodes for each harmonic)

Animation showing amphidromic systems and nodes - page where animation is from

Uni of Alaska

At and near the system's central point the tidal range is nil

The tidal range is zero at the amphidromic point and increases with distance from this point,

Principles of Tidal Sedimentology

Image from book

Elements of Marine Ecology

Essentials of Oceanography

Oceanography: An Invitation to Marine Science

Virginia Institute of Marine Science

page with many sources many no longer working

from an online Oceanography quiz

The center of an open-ocean tidal system is called a(n) __________.
(a) cotidal point
(b) amphidromic point
(c) ebb current
(d) tidal bore

(b) amphidromic point

The center of an open ocean tidal system is called a(n) __________.
(a) amphidromic center.
(b) cotidal center
(c) rotary center
(d) seiche
(e) tidal flux

(a) amphidromic center.

Due to the shape of the North Sea, it develops two amphidromic points.
(a) True
(b) False

(a) True

An amphidromic point is ____________.
(a) a "no tide" point in the ocean around which the tide crest rotates through one tidal cycle
(b) a place in the ocean where tides are highest
(c) a place in the ocean where tidal datum is displaced to the right (in the northern hemisphere),
or to the south (in the southern hemisphere)
(d) a "no tide" point at the coast where there is a daily high tide, but no low tide

(a) a "no tide" point in the ocean around which the tide crest rotates through one tidal cycle

New theory about currents (pdf)

The Tides, once more (perhaps the final word)

Just came across this on Physics Stack, excellent answer, and explanations of why there are no bulges moving under the moon.

Does Earth really have two high-tide bulges on opposite sides?

There is no tidal bulge.
This was one of Newton's few mistakes. Newton did get the tidal forcing function correct, but the response to that forcing in the oceans: completely wrong.
Newton's equilibrium theory of the tides with its two tidal bulges is falsified by observation. If this hypothesis was correct, high tide would occur when the Moon is at zenith and at nadir. Most places on the Earth's oceans do have a high tide every 12.421 hours, but whether those high tides occur at zenith and nadir is sheer luck. In most places, there's a predictable offset from the Moon's zenith/nadir and the time of high tide, and that offset is not zero.
One of the most confounding places with regard to the tides is Newton's back yard. If Newton's equilibrium theory was correct, high tide would occur at more or less the same time across the North Sea. That is not what is observed. At any time of day, one can always find a place in the North Sea that is experiencing high tide, and another that is simultaneously experiencing low tide.
Read the complete page for more info

(nor fair use to quote the entire article)

Archived here (let's all support

While there aren't actually two bulges, many many publications still show it, and teach it.
An example of a University course that teaches there are two bulges

Model of arctic tides

Hudson Strait tides (possibly the largest tides on the planet)

Earth tides

Earth tides and eartquakes

(edit June 27 2015)

Just found this blog post, I like his questions, ones anyone might ask when hearing the old (and wrong) explanation of the two bulges

Here is a 16 day animation from the TOPEX satellite that shows what tides actually look like worldwide.