The tidal range in a location depends on a number of factors, including the slope of the seafloor. Water appears to move a greater distance on a gentle slope than on a steep slope. So when the Sun and Moon are aligned, what do you expect the tides to look like? Waves are additive so when the gravitational pull of both bodies is in the same direction the high tides add and the low tides add Figure below. Highs are higher and lows are lower than at other times through the month.
These more extreme tides, with a greater tidal range, are called spring tides. Spring tides occur when the tidal bulges from the Moon and Sun are aligned. The Moon is full in this image; in the bottom image the Moon would appear as a new Moon. Neap tides are tides that have the smallest tidal range, and they occur when the Earth, the Moon, and the Sun form a 90 o angle Figure below.
How do the tides add up to create neap tides? At neap tides, the tidal range relatively small. Neap tides occur when the Earth, the Sun, and the Moon form a right angle; the Moon is in its first or third quarter. High tides occur about twice a day, about every 12 hours and 25 minutes. The reason is that the Moon takes 24 hours and 50 minutes to rotate once around the Earth so the Moon is over the same location 24 hours and 50 minutes later. Since high tides occur twice a day, one arrives each 12 hours and 25 minutes.
What is the time between a high tide and the next low tide? Some coastal areas do not follow this pattern at all. These coastal areas may have one high and one low tide per day or a different amount of time between two high tides. These differences are often because of local conditions, such as the shape of the coastline that the tide is entering. Skip to main content. The Ocean. Neap tides occur when the moon is in the first or third quarter - when the sun, earth and moon form a right angle.
The lunar high tide coincides with the solar low tide and they partly cancel out, giving a small total tide. The regular motion of the sun, moon and earth cause spring tides to occur roughly 36 to 48 hours after the full or new moon, and for any given location, always at roughly the same time of day. For example at Liverpool, the spring tides are generally around midnight and midday.
Not all spring tides are the same size. Springs nearest the equinoxes 21 March and 21 September — when day and night are of equal length all over the world are slightly bigger. The explanation for this is very complex and won't be given here. Back on earth, tides are affected by more mundane things, such as weather and the shape of the coastline.
In the upper reaches of estuaries the river bed and shape of the estuary can distort the tidal pattern, producing long flood times and short ebb times. Though the time from high tide to high tide is the same as usual — roughly 12 hours 25 minutes — low tide is not half way between them. At some places, the flood tide rises quickly after a period of low water lasting maybe four or five hours. This kind of geographical effect is very important, and because of it you should use local tide tables available from local newsagents and tackle shops when possible.
Cromer, Lowestoft and Aldeburgh are fairly close to each other on the East Anglian coast. However, high tide is hours apart at these places. This is precisely the opposite to Southend and Herne Bay, which face each other across the mouth of the Thames. Their tides differ by only a few minutes. Without detailed geographical information, it is impossible to predict these differences, so keep to local tide tables.
Geography also affects the tidal range. Tides are greatly influenced by the gravitational pull from the moon and sun. The moon's elliptic orbit means that twice a month, the moon, sun and Earth are in direct alignment and create a combined gravitational force.
In the open ocean, the tidal force of the moon will appear as bulges of water facing the moon whereas around land mass the water can spread out onto land creating tides.
There are two main tides that are higher or lower than average. They occur twice monthly and are called neap and spring tides. When there is a low tide, the Moon faces the Earth at a right angle to the Sun so the gravitational force of the Moon and Sun work against each other.
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