TIDES

Tides  Tides are long period waves that move in the ocean in response to the gravitational force of the sun and the moon.  Tides originate in the ocean and progress towards the coastline.

High and Low Tides  When the highest part, or crest of the wave reaches a particular location, high tide occurs; low tide corresponds to the lowest part of the wave, or its trough.  The difference in height between the high tide and the low tide is called the tidal range.

The cause of tides.  Gravity is one major force that creates tides. In 1687, Sir Isaac Newton explained that ocean tides result from the gravitational attraction of the sun and moon on the oceans of the earth.  Newton’s law of universal gravitation basically states, the greater the mass of two objects and the closer they are to each other, the greater the gravitational force between them.

The cause of tides con’t  The moon has a greater effect even though, based on its mass, the suns gravitational force is 177 times greater than the moon to earth. But because the sun is 390 times further from the earth than the moon, the sun’s effect on tides is 46% as much as the moon’s.

The Two Bulges  The moon attracts the water closest to it which creates what we call a bulge. This happens because the moon’s force of gravity overcomes the earth’s gravitational force.  A bulge is also created on the other side of the earth because the earth is being pulled away from the water, towards the moon.

A lunar day and high and low tide  A lunar day is the period of time it takes for the earth’s moon to complete one full rotation on its axis with respect to the sun.  Because the earth rotates through two tidal bulges every “lunar day” we get 2 high tides and 2 low tides every 24 hours and 50 minutes.  It takes 12 hours and 25 minutes for a high tide to occur. The time between high and low tide is 6 hours, 12 minutes and 30 seconds.

Spring and Solar Tides  Spring tides are extra high tides and very very low tides.  They are caused when the sun, moon and earth are in alignment and the solar and lunar tides are added together.  Solar tides are about half as large as lunar tides and are expressed as a part of lunar tide patterns, not as a separate set of tides.

Neap Tides  Neap tides are created when the moon is at a right angle to the sun. The solar tide partially cancels out the lunar tide so moderate tides are produced.  There are 2 sets of spring tides and 2 sets of neap tides in a lunar month.

Tidal Cycles  A diurnal tides is when only one high and one low tide take place each day. You might experience a diurnal tide in the gulf of Mexico.  A semi diurnal tide is when 2 high and 2 low tides takes place, with both being roughly the same height. You might find these tides on the eastern coast of North America.  A mixed semi diurnal tide is when 2 high and 2 low tides take place but have differing heights. This type of tide is common on the western coast of North America.