Monday, August 16, 2010

Sea Level

Sea level.

Everyone is familiar with the term "sea level." We all know what it means. Or do we?

Of course sailors know that the sea isn't really level. There are waves and tides and wind surges and storm runoffs and all sorts of other factors that affect the level of the sea. So we use "mean sea level", the average height of the ocean, often measured as the halfway point between the mean high tide and the mean low tide. Then we can measure tides and surges in relation to mean sea level, usually only a few feet up and down.

So mean sea level is.... ummm level. The same height all over the earth. Right?

Well, not exactly. It all depends on what you mean by "height". The variation in the distance of the mean sea level of the ocean as measured from the center of the earth varies by many miles from place to place. Yes... miles.

It's all because of the earth's rotation. The earth isn't a perfect sphere. It's an oblate spheroid. It bulges at the equator. You knew that, right?

The land bulges. The sea bulges. So what if we could magically make the seas and oceans really level? For example, what would happen if the earth stopped spinning one day? No more centrifugal force. No more bulging. Over time, the earth’s shape would approximate a perfect sphere, but the most immediate readjusting would be done by the oceans which currently bulge as much as 5 miles at the equator.

The picture at the top of this post (shamelessly stolen from Strange Maps) shows what the map of the earth's continents and oceans would look like if the earth stood still and the seas leveled themselves out. Goodbye Canada, Russia and Europe. Hello to an equatorial megacontinent ringing the globe and two polar oceans.

You could drive around the world on land. I guess some record breaking circumnavigators would eventually bike it, walk it or run it. Leaving aside the issue of what wind patterns there might be on a non-rotating earth, you couldn't do a sailing circumnavigation any more, at least not in the sense of a route that crosses the equator and crosses every meridian. The best you could do would be to sail a circuit of the Southern Ocean or a similar route crossing every meridian in the new Northern Ocean at the latitude of the USA/Canadian border.

How strange is that possum?


JP said...

If the Earth wasn't rotating a day would take a year, and hence you'd have long periods of very bright & hot and very cold & dark times.

The face away from the Sun would be deep winter that would last 6 months. Brrr!!!

So sailing around the world would be impossible unless you ice-sailed the frozen dark side of the Earth.

Tillerman said...

Exactly JP.

It could be, of course, that one side of the earth would always face the sun (a bit like the moon with respect to the earth.) Or in your scenario perhaps sailors would plan a "circumnavigation" to take a year so that they could always be sailing in the sun (and on liquid water.)

And then there's the whole issue of what kinds of winds would be generated on an earth where the earth and its atmosphere aren't warmed and cooled on a daily basis. And with no rotation there's no Coriolis force so presumably no circulation around high and low pressure areas.

This could be a whole other post...

JP said...

I wonder if on the boundary the wind would be like sea breezes.

Just much MUCH stronger!

JP said...

ps like the new graphic.

I feel like falling in (or was it out) and saluting.

Tillerman said...

Well I guess there would be a sea breeze effect at the land/sea boundaries. But then there would probably be an even stronger effect caused by the different temperatures between the light and dark sides of the planet. How would those two winds interact?

Venus, although not exactly analogous due to the high density of its atmosphere, has a very slow rotation rate. It has very strong (370 km/hr) winds from East to West at the top of the atmosphere, less strong at the surface of the planet, with an immense vortex at each pole. I haven't seen an explanation of why this should be so. Any theories?

O Docker said...

If you want to do frostbite races, you'll need to move to the dark side.

Some things never change.

Dennis @ Marine Electronics said...

Tillerman: What an interesting post. I like the map. Never thought of the Oceans being the same height, seems like an impractical notion given the winds/waves.

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