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Monday, November 4, 2013

Campobello In November

Yes, yes, yes…it’s getting colder but boy the sun is shining on this little piece of paradise. A wide blue sky made for a great fall day today. And even after the storm, there are still a lot of leaves on the trees. Some trees are still showing green. Our biggest maple tree has lost all leaves though, but it’s neighbour tree is still in fall mode.
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High tide                                                                    Low tide
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We still have northerly winds which brought the measured temperature of –1C (30F) to a wind chilled temp of ……well …way down.

Yet the afternoon was so nice that we took Molly on a walk along the south side of the island. It’s largely protected from the northern winds and with the sun shining it was downright warm. What en enjoyable walk.
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Bea had taken pictures of the tide up to it’s top and when it was way down. Looking at the beach we understand what enormous amounts of water is moving around on a daily basis. It’s nature’s way to contribute to clean waters, and making feed available to all the sea creatures.
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Herring Cove Beach                                                           Having a word with Molly 

For those of you who are not living by the sea or never have seen the tide move in or out here is an explanation of how this is actually  happening:
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A mossy patch along the path                            and Mountain Ash berries fallen down

Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon and the Sun and the rotation of the Earth.

Some shorelines experience two almost equal high tides and two low tides each day, called a semi-diurnal tide. Some locations experience only one high and one low tide each day, called a diurnal tide. Some locations experience two uneven tides a day, or sometimes one high and one low each day; this is called a mixed tide. The times and amplitude of the tides at a locale are influenced by the alignment of the Sun and Moon, by the pattern of tides in the deep ocean, and by the shape of the coastline.

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Tides vary on timescales ranging from hours to years due to numerous influences. To make accurate records, tide gauges at fixed stations measure the water level over time. Gauges ignore variations caused by waves with periods shorter than minutes. These data are compared to the reference (or datum) level usually called mean sea level.

While tides are usually the largest source of short-term sea-level fluctuations, sea levels are also subject to forces such as wind and barometric pressure changes, resulting in storm surges, especially in shallow seas and near coasts.

In most locations, the largest constituent is the "principal lunar semi-diurnal", also known as the M2 tidal constituent. Its period is about 12 hours and 25.2 minutes, exactly half a tidal lunar day, which is the average time separating one lunar zenith from the next, and thus is the time required for the Earth to rotate once relative to the Moon. Simple tide clocks track this constituent. The lunar day is longer than the Earth day because the Moon orbits in the same direction the Earth spins. This is analogous to the minute hand on a watch crossing the hour hand at 12:00 and then again at about 1:05½ (not at 1:00).

The Moon orbits the Earth in the same direction as the Earth rotates on its axis, so it takes slightly more than a day—about 24 hours and 50 minutes—for the Moon to return to the same location in the sky. During this time, it has passed overhead (culmination) once and underfoot once (at an hour angle of 00:00 and 12:00 respectively), so in many places the period of strongest tidal forcing is the above mentioned, about 12 hours and 25 minutes. The moment of highest tide is not necessarily when the Moon is nearest to zenith or nadir, but the period of the forcing still determines the time between high tides.

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Typical tide calendar, this one being for Vancouver, B.C. showing fluctuations in daily occurring tides. Our own tidal calendar shows a lot more regularity from tide to tide. (See below)

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Because the gravitational field created by the Moon weakens with distance from the Moon, it exerts a slightly stronger than average force on the side of the Earth facing the Moon, and a slightly weaker force on the opposite side. The Moon thus tends to "stretch" the Earth slightly along the line connecting the two bodies. The solid Earth deforms a bit, but ocean water, being fluid, is free to move much more in response to the tidal force, particularly horizontally. As the Earth rotates, the magnitude and direction of the tidal force at any particular point on the Earth's surface change constantly; although the ocean never reaches equilibrium—there is never time for the fluid to "catch up" to the state it would eventually reach if the tidal force were constant—the changing tidal force nonetheless causes rhythmic changes in sea surface height.

Why is the tide higher in Newfoundland than here on Campobello?

Land masses and ocean basins act as barriers against water moving freely around the globe, and their varied shapes and sizes affect the size of tidal frequencies. As a result, tidal patterns vary. As the Bay of Fundy narrows in the north the moving tidal waters have to “squeeze in” a tighter space. Measurements made in November 1998 at Burntcoat Head in the Bay of Fundy recorded a maximum range of 16.3 meters (53 ft) and a highest predicted extreme of 17 meters (56 ft), while Campobello experiences up to 28ft of tide. Tides are also less noticeable in the south.  Extremely small tides also occur for the same reason in the Gulf of Mexico.

 

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