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Curious Facts About the Tides
Visitor: “I have always been told that the tides come an hour later each day, but from my observation it would appear that this is not always so. Can you tell me about this? Also, I am curious as to why sometimes the morning is higher than the afternoon tide, and why sometimes it is the other way round?”
Cape Codder: “Well, it’s like this: The tides, roughly reckoning them, do come in an hour later each day. Actually, as you have observed, we have two tides every day, or more accurately, every 24 hours, 50 minutes, and 38 seconds. Of course, the time of each tide and its height can both be somewhat affected by the existing local weather conditions. If there is a powerful onshore wind blowing as the tide comes in, the wind will help to build up a somewhat higher and perhaps somewhat earlier tide. If the wind is blowing against the tide, that may check the height of the tide.”
“The chief force that governs our tides is the mighty attraction of the moon. The sun of course plays a part in producing them, but the sun is 93,000,000 miles away and the moon only 240,000 miles away, so the lunar (moon-caused) tides are far more resultful than the solar (sun-caused) ones.”
Visitor: “But why do we have a high tide, and a low tide?”
Cape Codder: “The strongest tides are the high tides. The high tides alternate with the low tides once with each rotation of the earth. When the sun and the moon are in a line on the same side of the earth, a very strong tide is produced. The tides are weakest when the sun and the moon are in opposite positions. The strong tides so produced are called spring tides; the weak ones are called neap tides. It is the varying positions which the sun and the moon assume from day to day which account for our high and low tides.”
Visitor: “Can sailors at sea notice the high tide and the low tide?”
Cape Codder: “No, for tides are quite unnoticeable in open water; ships rise or fall with the great mass of water without the sailors’ ever being conscious of tides. Although in some areas the flooding and ebbing tide can cause a significant tidal current which can affect the speed and drift of a vessel at sea. But along shore it is very different looking.”
Visitor: “What should I call a tide that is coming in, or going out?”
Cape Codder: “When a tide is coming in (before high tide), it is known as the flooding or flood tide. When the tide is going out (before low tide), it is called the ebbing or ebb tide.”
Visitor: “How high do tides make up?”
Cape Codder: “The difference, vertically, between the crest of a rising tide and the trough (depression) of a low tide is usually only two or three feet, but in certain broad open bays the differences may be very great, as much even as fifty-four feet. There are rip tides, too, which have a choppy surface as they come in, and the bore, which rushes in like a river over mud flats.”
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Categories: Boating, Nature
Keywords: boating, maritime, nature, tides, high tide, low tide, tidal current
Comments:
I was in Truro last week, while watching the sunset over P.Town, one of my fellow vacationers said the sun sets in the East in Cape Cod, one of only 2 places known. Is this true, it looked North (and west) to me?
Posted by Kerri from Albany, NY on 08/18/08 at 03:51 PM | #
Kerri, you are right.
The sun sets in the West. It rises in the East. One your fellow vacationers is sadly misinformed.
I’m doing a research project about the tides. I have to find out why the tides come in farther on either sides of the canal. Do you know why or anywhere I could find this information?
Posted by Evan on 11/01/09 at 10:38 PM | #
Evan,
Try this:
Tides in marginal seas and bays cannot be directly forced; they are co-oscillation tides generated by tidal movement at the connection with the ocean basins. Depending on the size of the sea or bay they take the shape of a seiche or rotate around one or more amphidromic points.
If the tidal forcing is in resonance with a seiche period for the sea or bay, the tidal range is amplified and can be enormous. This produces the largest tidal ranges in the world ocean
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Very interesting and informative! I never knew this about tides! I’ve always been fascinated with the ocean and everything about it, especially tides! My husband was a Merchant Marine Engineering Officer retiring after almost 30 years.
Thank you!