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Re: Big Full Moon and Perigee Spring Tides
From: Robert Eno
Date: 2011 Mar 20, 11:26 -0400

Spring tides result in a very interesting phenomenon in my part of the world where the sea freezes over from about November up until mid-June. It is also worth mentioning that we have a tidal range of up to 38 feet (11 meters).

Twice per month, the spring tides cause water to seep up from under the ice in the near-shore tidal zone resulting in a substantial layer of liquid water on top of the ice. This in turn, creates a solid wall of fog along the shore. Accessing the sea ice at this time becomes problematic. When the tide recedes, the layer of water quickly freezes over in the minus 30 to 35 C temperature. By the time break up arrives we have very thick layer of ice from the shore out to about 50 yards.

Another interesting aspect of this phenomenon is how it affects poor hapless and lazy small boat owners who simply leave their boats a few yards up from the high water mark in the fall. These boats become encased in ice with only the tip of the bow and part of the engine visible by about February. You can imagine what the salt water does to their engines.

Back in 1999, a company left a string of 9 barges here. They were ordered into port by the Coast Guard who didn't believe that they would survive the perilous journey down the storm-ridden Labrador Coast. The barges were stacked, one on top of one another in threes. The company beached the barges in October of that year and by the time they returned in June 2000 to prepare to take them to their home port, the barges were sitting on top of a 5 foot-thick pinnacle of ice that had built up layer by layer over the previous 8 months. The ice melted unevenly under the barges which resulted in one of them becoming punctured (from the sheer weight of the barge resting on an increasingly narrower pinnacle of ice) and releasing oil into the sea.

Robert

----- Original Message -----

From: Frank Reed

To: NavList@fer3.com

Sent: Sunday, March 20, 2011 7:22 AM

Subject: [NavList] Re: Big Full Moon and Perigee Spring Tides

John H, you wrote:
"I'm at Cape Cod today, and we do have some big tides today, so that much is interesting."

Also note that there is a lag of about a day for Spring Tides on the Atlantic coast of the US. The ocean tides are like a big set of coupled, driven harmonic oscillators. The driving force has numerous frequencies. The most important frequencies, of course, are the daily rates for the Sun and the Moon to pass over any point on the Earth. Since they're different frequencies, they generate different responses in the driven oscillators with slightly different phases. That yields the delay in the Spring Tides. This delay is different in different parts of the world. As I said, here on the Atlantic coast of the US, it's about a day. In northwest Europe, two days or more. On the Pacific coast of the US, close to zero, and there are even a few spots around the globe where the Spring Tides lead the phase of the Moon by a couple of days. This lag was one of the first things that I brought up on NavList way back in December of 2003. I was interested because early editions of Bowditch still described European conditions and back then there were ZERO 19th century editions of Bowditch available online. Now there are dozens.

-FER

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