CSIRO ScienceImage 10726 The effects of a king tide on Queenslands Gold Coast

A king tide is an especially high

spring tide Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables ...

, especially the

perigean spring tide A perigean spring tide is a tide that occurs three or four times per year when a perigee (the point nearest Earth reached by the Moon during its 27.3-day elliptic orbit) coincides with a spring tide (when the Sun, the Moon, and Earth are nearly ...

s which occur three or four times a year. King tide is not a scientific term, nor is it used in a scientific context. The expression originated in

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

New Zealand New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...

and other

Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is bounded by the cont ...

nations to describe especially high tides that occur a few times per year. It is now used in North America as well, particularly in low-lying

South Florida South Florida, sometimes colloquially shortened to SoFlo, is the Regions of the United States#Florida, southernmost region of the U.S. state of Florida. It is one of Florida's three most commonly referred to directional regions; the two others are ...

, where king tides can cause tidal flooding. In Vancouver, Canada, king tides are a growing problem along its seawall.

Definition

King tides are the highest tides. They are naturally occurring, predictable events. Tides are the movement of water across

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

's surface caused by the combined effects of the

gravitation In physics, gravity (), also known as gravitation or a gravitational interaction, is a fundamental interaction, a mutual attraction between all massive particles. On Earth, gravity takes a slightly different meaning: the observed force b ...

al forces exerted by the

Moon The Moon is Earth's only natural satellite. It Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

, and the rotation of Earth which manifest in the local rise and fall of sea levels. Tides are driven by the relative positions of the Earth, Sun, Moon, land formations, and relative location on Earth. In the lunar month, the highest tides occur roughly every 14 days, at the new and full moons, when the gravitational pull of the Moon and the Sun are in alignment. These highest tides in the lunar cycle are called spring tides. The proximity of the Moon in relation to Earth and Earth in relation to the Sun also has an effect on tidal ranges. The Moon moves around Earth in an

elliptic orbit In astrodynamics or celestial mechanics, an elliptical orbit or eccentric orbit is an orbit with an eccentricity of less than 1; this includes the special case of a circular orbit, with eccentricity equal to 0. Some orbits have been referre ...

that takes about 29 days to complete. The gravitational force is greatest when the Moon is at

perigee An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. The line of apsides (also called apse line, or major axis of the orbit) is the line connecting the two extreme values. Apsides perta ...

closest to Earthand least when it is at

apogee An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. The line of apsides (also called apse line, or major axis of the orbit) is the line connecting the two extreme values. Apsides perta ...

farthest from Earthabout two weeks after perigee. The Moon has a larger effect on the tides than the Sun, but the Sun's position also has an influence on the tides. Earth moves around the Sun in an

that takes a little over 365 days to complete. Its

gravitational force Newton's law of universal gravitation describes gravity as a force by stating that every particle attracts every other particle in the universe with a force that is proportional to the product of their masses and inversely proportional to the sq ...

is greatest when the Earth is at perihelionclosest to the Sun in early Januaryand least when the Earth is at aphelionfarthest from the Sun in early July. The king tides occur at new and full moon when the Earth, Moon and Sun are aligned at perigee and

perihelion An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. The line of apsides (also called apse line, or major axis of the orbit) is the line connecting the two extreme values. Apsides perta ...

, resulting in the largest tidal range seen over the course of a year. So, tides are enhanced when the Earth is closest to the Sun around January 2 of each year. They are reduced when it is furthest from the Sun, around July 2. The predicted heights of a king tide can be further augmented by local weather patterns and ocean conditions.

References

General references

tidesandcurrents.noaa.gov

Definition

References

General references

Inline citations

External links