Importance of Geography and Topography
The distance between continents as well as the depth and shape of the ocean are key factors in determining seawater level along the shores. In areas where the continents are close together, such as the northern parts of North America, Europe and Asia, the difference between high and low tide is huge compared to areas down south, where the continents are farther apart.
Average and Extreme Tides
Mid-ocean has an average tidal range around 3 feet or 1 meter. However, the tidal range in some coastal areas can be ten times higher than most extreme regions. Because of how the tidal range varies from place to place, it is not sensible to give an average for tidal range along coastlines on Earth.
The Bay of Fundy in Canada holds the record for the world’s highest tide; in this region, the difference between low and high tide is about 16.3 meters (53.3 feet). In the United States, the highest tides can reach 12.2 meters (40 feet) close to Anchorage, Alaska. The tidal range varies along the coast of the UK; it can vary from as low as 0.5 meters (1.6 feet) to as high as 15 meters (50 feet).
Tidal range is also influenced by the Moon’s phase. And the greatest difference between low and high tide take place around New Moon and Full Moon. During these phases, both the solar and lunar tide coincides because the Moon and Sun are aligned with the Earth, and both the Sun and Moon’s gravitational forces combine in pulling the ocean’s water in the same direction. This term is referred to as Spring tides or king tides, and it has no relationship with the season of spring, instead, the term is a synonym for jump or leap or is derived from the concept of the tide “springing forth”.
An equinoctial spring tide is when a spring tide coincides with the March or September equinox. We can expect the largest tidal range of the year during this period because the Moon and Sun are aligned with the equator at the equinoxes.
Perigean and Apogean Spring Tides
A perigean spring tide occurs several times in a year; it is also called a proxigean spring tide. This happens when the Moon, either New or Full, is close to the earth – perigee. This is commonly referred to as a Supermoon, and it causes a greater variation between high tides and low tides. However, in a typical spring tide, the difference is about 5 cm or 2 inches.
An apogean spring tide is the opposite of perigean spring tide, during this period, the Moon, either New or Full Moon, is farthest from the Earth resulting in smaller lunar tide. This is referred to as apogee or Micromoon. The apogean spring tides are around 5cm or 2 inches less than the normal spring tides.