Mixed Tide
Introduction
Mixed tides are a type of tidal pattern that features two high tides and two low tides of different heights per tidal day. They are common in many coastal regions around the world, particularly along the Pacific coast of North America. Mixed tides are a result of the complex interaction between the gravitational forces exerted by the moon and the sun, and the rotation of the Earth.
Understanding Tides
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon and the Sun, and the rotation of the Earth. Tides vary on timescales ranging from hours to years due to numerous factors. The primary factors are the gravitational force of the Moon and Sun, the rotation of the Earth, the Earth's position in its orbit around the Sun, and the depth and shape of the ocean floor.
Types of Tides
There are three main types of tides: diurnal, semidiurnal, and mixed.
Diurnal Tides
Diurnal tides have one high tide and one low tide each day. These tides occur when the moon is directly above or below the equator.
Semidiurnal Tides
Semidiurnal tides have two high tides and two low tides each day of approximately the same height. These tides occur when the moon is above or below the tropics.
Mixed Tides
Mixed tides, the focus of this article, have two high tides and two low tides each day, but the heights of the tides are different. These tides occur when the moon is above or below intermediate latitudes.
Characteristics of Mixed Tides
Mixed tides are characterized by significant variation in the height of successive high and low tides. The difference in height between successive high tides or low tides is known as the diurnal inequality. The diurnal inequality is greatest when the moon is furthest from the equator, and least when the moon is directly above or below the equator.
Causes of Mixed Tides
Mixed tides are caused by the interaction of two different tidal frequencies: the diurnal frequency, which is caused by the rotation of the Earth, and the semidiurnal frequency, which is caused by the gravitational pull of the Moon and the Sun. The combination of these two frequencies results in a complex tidal pattern with two high tides and two low tides each day, of different heights.
Locations of Mixed Tides
Mixed tides are most common along the Pacific coast of North America, but they can also be found in many other coastal regions around the world. The specific characteristics of mixed tides, including the degree of diurnal inequality and the timing of high and low tides, can vary widely from place to place.
Impact of Mixed Tides
Mixed tides can have a significant impact on coastal environments and human activities. They can affect the distribution of marine species, the formation of coastal landforms, and the operation of ports and harbors. Understanding the patterns and causes of mixed tides is therefore important for a wide range of scientific, environmental, and economic applications.