Types Of Tides
Tides vary in their frequency, direction, and movement from place to place and also from time to time.
- Tides may be grouped into various types based on their frequency of occurrence in one day or based on their height.
Semi-Diurnal Tide:
- It is the most common tidal pattern, featuring two high tides and two low tides each day.
- The successive high or low tides are approximate of the same height.
Diurnal Tide:
- There are only one high tide and one low tide each day.
- The successive high and low tides are approximate of the same height.
Mixed Tide:
- Tides having variations in height are known as mixed tides.
- These tides generally occur along the west coast of North America and on many islands of the Pacific Ocean.
Tides based on positions of Sun, Moon, and Earth
- The height of rising water (high tide) varies appreciably depending upon the position of sun and moon with respect to the earth.
Spring Tide:
- When the sun, the moon, and the earth are in a straight line, the height of the tide will be higher. These are called spring tides.
- They occur twice a month, one on full moon period and another during the new moon period. Neap Tide:
- The sun and moon are at right angles to each other and the forces of the sun and moon tend to counteract one another. The Moon’s attraction, though more than twice as strong as the sun’s, is diminished by the counteracting force of the sun’s gravitational pull.
- Normally, there is a seven-day interval between the spring tides and neap tides. Thus neap tides also occur twice a month (during the first and last quarter moon).
- The tidal range is greater than normal at perigee (moon’s orbit closest to earth) and perihelion (earth is closest to the sun) while it is lower than normal at apogee (moon’ orbit farthest from earth) and aphelio (earth is farthest from sun).