Kelvin Waves and their effect on Tidal Range.

[Mark-1]

I'm reading "The Walker's Guide to Outdoor Clues and Signs" by Tristan Gooley. (http://www.amazon.co.uk/gp/product/B00H4EPBWM?btkr=1)

In it he says:

West facing shores see bigger tidal ranges on average than east facing shores. This is because the direction of the rotation of the Earth sets up east-moving waves in the oceans, called Kelvin Waves.

To what extent is this true? Do west facing shores have bigger ranges than east? If so, is it largely due to Kelvin Waves?

 

[lpdsn]

I'm reading "The Walker's Guide to Outdoor Clues and Signs" by Tristan Gooley. (http://www.amazon.co.uk/gp/product/B00H4EPBWM?btkr=1)

In it he says:

West facing shores see bigger tidal ranges than east facing shores. This is because the Earth sets up east-moving waves in the oceans, called Kelvin Waves.

To what extent is this true? Do west facing shores have bigger ranges than east? If so, is it largely due to Kelvin Waves?

Aren't all waves at boundaries between fluids Kelvin Waves? Why should they be particularly east-moving?

 

[William_H]

I know very little about tides and why they are bigger in some places than others. However I live on a west facing shore of Oz (next stop S Africa) at 32 degrees south. We get remarkably small tide changes. Indeed prevailing winds and atmospheric pressure change seems to be as significant as the moon and sun. ie mostly .5 metre high to low.
Yet 2000km up the coast at Broome they get tides equalling UK tides. Or in Tasmania also exposed to Southerly Ocean to the west they get largish tides. It is all a mystery but certainly notr explained by west facing shore. olewill

 

[guernseyman]

Two types of Kelvin wave: equatorial and coastal.
The former travel eastwards i.e. towards a west coast but occur only at the equator.
The latter travel along a coast with the coast to the right in the northern hemisphere.

 

[Hydrozoan]

It’s very broadly true that west facing shores in the northern hemisphere have bigger tidal ranges, as the last map here (of the major ocean amphidromes and tidal ranges) shows: http://moocs.southampton.ac.uk/oceans/2014/11/09/amphidromic-points-tidal-spiders-in-a-real-world/. But on a local scale it may not be so because of the interaction of the tidal forcings with local basin topography, as the first diagram at that link shows for the North Sea.

Actually, the North Sea example is portrayed rather more clearly in colour here: http://gyre.umeoce.maine.edu/physicalocean/Tomczak/IntroOc/notes/figures/fig11a5.html, from which you can more easily see the larger tidal range along the east facing British coast and the smaller range along the west facing continental coasts. The dominant tidal effect over most of the North Sea is the tidal wave entering from the Atlantic in the north, rather than that through the Channel. The wave travels with the coast to the right as Guernseyman notes, propagating anticlockwise around the amphidrome and giving higher ranges on the British coast.

The first link gives broad descriptions of tidal evolutions in relation to topography, but it doesn’t mention Kelvin waves as such. Fundamentally, a Kelvin wave is a wave resulting from a balancing of rotation and a boundary, and as this short page http://web.vims.edu/physical/research/TCTutorial/dynamic.htm puts it: ‘Roughly speaking, you have a Kelvin wave – or a trapped wave as it is sometimes called - in your coffee cup when you swirl it to the left or right’. It goes on to link that simple description to the rotary waves in a tidal basin around an amphidromic point – which takes you back to the first link (which uses a rectangular tank, not a coffee cup, to represent a basin).

 

[Mark-1]

Thanks Hydrozoan!