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The tide is the regular rising and falling of the ocean's surface caused by changes in gravitational forces external to the Earth. The primary changing gravitational field is due to the Moon while the secondary field is caused by the Sun.
The maximum water level is called high tide; the minimum level is low tide. At any given point on the ocean, there are normally two high tides and two low tides each day. On average, high tides occur 12 hours 24 minutes apart. The 12 hours is due to the Earth's rotation, and the 24 minutes to the Moon's orbit. The 12 hours is half of a solar day and the 24 minutes is half of a lunar extension, which is 1/(29-day lunar cycle).
The height of the high and low tides (relative to mean sea level) also varies. Around new and full Moon, the tidal forces due to the Sun reinforce those of the Moon. The tide's range is at its maximum: this is called the spring tide, or just springs. When the Moon is at first quarter or third quarter, the forces due to the Sun partially cancel out those of the Moon. At these points in the Lunar cycle, the tide's range is at its minimum: this is called the neap tide, or neaps.
The relative distance of the Moon from the Earth also affects tide heights: When the Moon is at perigee the range increases, and when it is at apogee the range is reduced. Every 7˝ lunations, perigee and (alternately) either a new or full Moon coincide; at these times the range of tide heights is greatest of all, and if a storm happens to be moving onshore at this time, the consequences (in the form of property damage, etc.) can be especially severe ( surfers are aware of this, and will often intentionally go out to sea during these times, as the waves are more spectacular than ever).
In most places there is a delay between the phases of the Moon and its effect on the tide. Springs and neaps in the North Sea, for example, are two days behind the new/full moon and first/third quarter, respectively. The reason for this is that the tide originates in the southern oceans, the only place on the globe where a circumventing wave (as caused by the tidal force of the Moon) can travel unimpeded by land.
The resulting effect on the amplitude, or height, of the tide travels across the oceans. It is known that it travels as a standing wave northwards over the Atlantic. This causes relatively low tidal ranges in some locations (knots) and high ones in other places. This is not to be confused with tidal ranges caused by local geography, as can be found in Nova ScotiaNova Scotia ( In Detail) ( In Detail) Motto: Munit Haec et Altera Vincit (One defends and the other conquers Capital Halifax Largest City Halifax Area Total % fresh water 12th largest(9th lgst prov. 55 284 km˛ 3. 5% Population Total (2001) Density Ranked, BristolThis article is about the English city of Bristol. For other uses please see Bristol (disambiguation). Bristol is a city in south-western England, on the River Avon. It borders on the Unitary Districts of Bath and North East Somerset, North Somerset and S, the Channel IslandsAlternative meaning: Channel Islands (California The Channel Islands are a group of islands off the coast of Normandy, France, in the English Channel. They comprise two separate bailiwicks: the Bailiwick of Guernsey and the Bailiwick of Jersey. History Ma, and the English ChannelThe English Channel is the part of the Atlantic Ocean that separates the island of Great Britain from northern France, and joins the North Sea to the Atlantic. In French it is called La Manche ("the sleeve"). It is about 350 miles long and at its widest i. In these places tidal ranges can be over 10 metres.
The Atlantic tidal wave arrives after approximately a day in the English Channel area of the EuropeFor the band of the same name, see Europe (band . Europe is a continent forming the westermost part of the Eurasian supercontinent. Europe is bounded to the north by the Arctic Ocean, to the west by the Atlantic Ocean, to the south by the Mediterranean Sean coast and needs another day to go around the British islands in order to be effective in the North Sea. Peaks and lows of the Channel wave and North Sea wave meet in Dover Strait / Pas de Calais at about the same time but generally favour a current in the direction of the North Sea.
The exact time and height of the tide at a particular coastUnited States postal stamp. A coast is that part of an island or continent that borders an ocean, gulf, sea, or large lake. In geology and geography, the coast extends inland from the shoreline. The terms coast and coastal refer to the condition of beingal point is also greatly influenced by the local topography. There are some extreme cases: the Bay of Fundy, on the east coast of Canada, features the largest tidal range in the world, 16 metres (53 feet), because of the shape of the bay. Southampton in the United Kingdom has a double high tide caused by the flow of water around the Isle of Wight, and Weymouth, Dorset has a double low tide because of the Isle of Portland. Also there is only a slight tide in the Mediterranean due to the narrow connection with the ocean.