Semidiurnal

Definition

Semidiurnal refers to a tidal pattern that experiences two high tides and two low tides each day, with a period of approximately 12 hours and 25 minutes between consecutive high or low tides. This tidal cycle is closely linked to the Moon's influence on the Earth's oceans.

5 Must Know Facts For Your Next Test

1. The semidiurnal tidal pattern is the most common type of tidal cycle, occurring in many coastal regions around the world.
2. The two high tides and two low tides each day are caused by the Moon's gravitational pull on the Earth's oceans, which creates a bulge of water on the side of the Earth closest to the Moon and on the opposite side.
3. The period of approximately 12 hours and 25 minutes between consecutive high or low tides is due to the Moon's orbital period around the Earth, which is slightly longer than a 12-hour cycle.
4. Semidiurnal tides are influenced by the relative positions of the Sun and Moon, with the highest tides (spring tides) occurring when the Sun and Moon are aligned, and the lowest tides (neap tides) occurring when the Sun and Moon are at right angles to each other.
5. The tidal range, or the difference between high and low tide, can vary significantly depending on the phase of the Moon and the location, with some coastal areas experiencing very large tidal ranges and others experiencing relatively small tidal ranges.

Review Questions

• Explain how the Moon's gravitational pull contributes to the semidiurnal tidal pattern.
  • The Moon's gravitational pull on the Earth's oceans creates a bulge of water on the side of the Earth closest to the Moon and on the opposite side. This results in two high tides and two low tides each day, with a period of approximately 12 hours and 25 minutes between consecutive high or low tides. The semidiurnal tidal pattern is directly linked to the Moon's orbital period around the Earth, which is slightly longer than a 12-hour cycle.
• Describe how the relative positions of the Sun and Moon affect the tidal range in a semidiurnal tidal system.
  • The tidal range, or the difference between high and low tide, is influenced by the relative positions of the Sun and Moon. When the Sun and Moon are aligned (during new moon or full moon), their gravitational forces combine, resulting in the highest tides, known as spring tides. Conversely, when the Sun and Moon are at right angles to each other (during the first and third quarters), their gravitational forces partially cancel out, leading to the lowest tides, known as neap tides. This variation in tidal range is a key feature of the semidiurnal tidal pattern.
• Evaluate the significance of the semidiurnal tidal pattern in the context of coastal ecosystems and human activities.
  • The semidiurnal tidal pattern plays a crucial role in shaping coastal ecosystems, as the regular fluctuations in water levels and exposure to air can significantly impact the distribution and survival of marine organisms. Additionally, the semidiurnal tidal cycle has important implications for human activities in coastal regions, such as navigation, fishing, and the operation of coastal infrastructure like harbors and marinas. Understanding the predictable nature of the semidiurnal tidal pattern allows for the planning and scheduling of various coastal activities, highlighting the importance of this phenomenon in the interaction between the Earth, the Moon, and human societies.

Related terms

Diurnal:

A tidal pattern that experiences one high tide and one low tide each day, with a period of approximately 24 hours between consecutive high or low tides.

Tidal Range:

The vertical distance between the high tide and the subsequent low tide, which varies depending on the position of the Moon and Sun relative to the Earth.

Neap Tide:

A tide with a relatively small tidal range, occurring when the gravitational pull of the Moon and Sun are at right angles to each other, partially canceling out their effects.