The tides are a timeless and fascinating spectacle! Twice a day, the waves retreat from the shore before inexorably rising again. This natural phenomenon is caused by 2 main factors: the rotation of the Earth and the gravitational interactions between the Earth, the Moon and the Sun.
Effects of the Sun and Moon on tides
Tides are greatest during the New Moon and Full Moon , when the effects of the Sun and Moon add together. We then speak of Spring Tides (tidal coefficients > 70).
Conversely, during the first and last quarter moon, the effects of the Sun and the Moon attenuate each other. We then speak of Neap Tides (tidal coefficients < 70).
What are the different types of tide?
There are 3 main types of tides: diurnal tides, semidiurnal tides and mixed tides.
- diurnal tides : they occur once a day, with a high tide and a low tide of different levels. This means that there is a complete tidal cycle approximately every 24 hours and 50 minutes. Diurnal tides are generally observed in regions near the equator.
- semidiurnal tides : this is the most common type of tide in the world. They occur when the region experiences two high tides and two low tides of relatively equal magnitude per day. The semi-diurnal tidal cycle lasts approximately 12 hours and 25 minutes, corresponding to half of a lunar day. Coastal regions of most of the world's oceans experience semidiurnal tides.
- mixed tides : mixed tides are a mixture of diurnal and semi-diurnal tides. They occur when the region experiences two high tides and two low tides. They are generally observed in coastal regions where local shoreline configurations, ocean depths and current interactions lead to variations in tidal amplitudes.
Where are semidiurnal tides found?
Semi-diurnal tides occur in many locations around the world, especially in coastal regions. These tides consist of two high tides and two low tides each day, with approximately equal intervals between them. Some areas known for experiencing semi-diurnal tides include:
- Atlantic Coast of North America: Places like the Gulf of Maine, the Bay of Fundy, and along the Eastern Seaboard
- British Isles: Around the coasts of the United Kingdom and Ireland
- Western Europe: Coastal areas along the North Sea and the English Channel
- Western Africa: Regions along the Gulf of Guinea and the Atlantic coast of Africa
- Australia: Many coastal areas around Australia, including the east, west, and southern coasts
- Southeast Asia: Coastal regions around the Indonesian archipelago, the Philippines, and other parts of Southeast Asia
A tide clock is configured to operate with this type of tide.
(See how a tide clock works )
Areas with semi-diurnal tides