metomodule13

• Tide - the alternate rising and falling of the surface of the ocean and of water bodies (such as gulfs and bays) connected with the ocean that occurs usually twice a day and is the result of differing gravitational forces exerted at different parts of the earth by another body (such as the moon or sun).
• High tides and low tides are stages of the tidal cycle. They happen in periods of around 6 hours between each other and represent both the highest and lowest level of water of a specific location along the coastline.
• Diurnal tide – 1 high water and 1 low water each tidal day.
• Semi-diurnal tide – 2 high water and 2 low water each tidal day but have small differences between the heights of 2 consecutive high and low water.
• Mixed Semi-diurnal tide – large difference between the heights of 2 consecutive high and low water.
• The observable rise and fall of the sea level is influenced strongly by shoreline topography, ocean currents and the distribution of the continents.
• The moon's gravitational force is the main influence of a tidal cycle. Whether it is a semidiurnal tide or diurnal tide the pull from the moon and proximity of the moon to the earth is the largest factor to why tides occur.
• Spring tide – tides with higher high and lower low. Occurs at the time of new moon and full moon (sun and moon are conjunction and at opposition with the earth.
• Neap tide - seven days after a spring tide—refers to a period of moderate tides when the sun and moon are at right angles to each other. Tides with lower high and higher low, occur at time of first and third quarters (sun and moon are in quadrature with the earth).
• PERIGEAN TIDE-When the moon is nearest to the earth in its orbit (at perigee), its tide-producing power is greater than average, resulting in perigean tides (lunar semidiurnal increase). These are 15-20 per cent greater than average.
• APOGEAN TIDE-When the moon is farthest from the earth (in apogee), the tides are called apogean tides, which are about 15-20 per cent less than average. Coincidence of spring and perigean tides results in an abnormally great tidal range, while when neap and apogean tides coincide the range is abnormally small.