7.1 Tidal forces and tidal patterns
3 min read•july 24, 2024
Gravitational forces from the Moon and Sun create Earth's tides, causing water to rise, fall, and flow horizontally. These forces result in different tidal patterns: spring tides during new and full moons, and neap tides during quarter moons.
Tidal patterns vary globally, with diurnal, semidiurnal, and mixed types. Factors like coastal topography, continental shelf width, latitude, and resonance affect and currents, creating unique conditions in different locations worldwide.
Gravitational Forces and Tidal Patterns
Gravitational forces of tides
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- Moon's gravitational pull primarily influences Earth's tides creates two tidal bulges facing the moon and opposite side of Earth
- Sun's gravitational pull secondarily influences tides enhances or diminishes lunar tides depending on alignment (new moon, full moon)
- Effects on Earth's oceans include vertical movement of water (rise and fall) and horizontal movement of water (tidal currents)
- Tidal range measures difference between high and low tide levels varies globally (Bay of Fundy, Nova Scotia: 16m)
Spring vs neap tides
- Spring tides occur during new and full moon phases when Sun, Moon, and Earth align (syzygy) resulting in higher high tides and lower low tides
- Neap tides occur during first and third quarter moon phases when Sun and Moon form right angle with Earth resulting in lower high tides and higher low tides
- Lunar phase relationship links spring tides to new moon and full moon (0° and 180°) and neap tides to first quarter and third quarter moon (90° and 270°)
Types of tidal patterns
- feature one high tide and one low tide per day in approximately 24-hour cycle common in Gulf of Mexico and parts of Southeast Asia (Thailand)
- have two high tides and two low tides per day in approximately 12-hour cycle most common globally prevalent along Atlantic coasts (East Coast USA)
- combine diurnal and semidiurnal patterns with two high tides and two low tides of different heights common along Pacific coasts of North America (California)
Factors influencing tidal range
- Coastal topography affects tidal range narrow bays and estuaries amplify range (Bay of Fundy) while wide, open coastlines have smaller ranges (Florida)
- Continental shelf width impacts tidal range broad shelves increase range (North Sea) narrow shelves decrease range (West Coast Africa)
- Latitude generally correlates with tidal range higher latitudes experience larger ranges (Alaska) compared to lower latitudes (Caribbean)
- Resonance effects in enclosed basins can amplify tidal range when natural period of oscillation matches tidal forcing (Gulf of Mexico)
- Bathymetry influences tidal currents shallow areas experience stronger currents (English Channel) while deeper areas have weaker currents
- deflects currents to the right in Northern Hemisphere and to the left in Southern Hemisphere affecting tidal circulation patterns
- Coastal geometry modifies current patterns headlands and bays create complex flow structures (San Francisco Bay)
- Tidal range generally correlates with current strength larger ranges produce stronger currents (Strait of Magellan)
- Location-specific influences:
- Bay of Fundy experiences extreme tidal range due to resonance and funnel shape
- Mediterranean Sea has minimal tides due to narrow connection to Atlantic Ocean
- Cook Strait, New Zealand features strong tidal currents due to narrow passage between islands
Key Terms to Review (21)
Centrifugal force: Centrifugal force is an apparent force that acts outward on a mass moving in a circular path, caused by the inertia of the mass itself. In the context of tides, this force, in conjunction with gravitational pull from celestial bodies like the moon and sun, contributes to the creation of tidal patterns in oceans. It helps explain why there are two high tides and two low tides each day as the Earth rotates and these forces interact.
Coriolis Effect: The Coriolis Effect is the apparent deflection of moving objects, such as air and water, due to the rotation of the Earth. This phenomenon influences large-scale patterns of movement in the atmosphere and oceans, affecting everything from wind patterns to ocean currents, ultimately playing a significant role in climate and weather systems.
Diurnal Tides: Diurnal tides are a type of tidal pattern characterized by a single high tide and a single low tide each lunar day, typically occurring approximately every 24 hours. This tidal behavior is most commonly observed in certain coastal regions where the gravitational pull of the moon and sun creates a distinct and predictable rhythm of water movement. The uniqueness of diurnal tides influences local marine ecosystems, navigation, and coastal activities.
Gravitational Force: Gravitational force is the attractive interaction between two masses, determined by their mass and the distance separating them. In the context of celestial bodies, this force is primarily responsible for the movement of planets, moons, and other astronomical objects. It plays a crucial role in creating tidal forces that affect oceans and create patterns of tides on Earth.
Harmonic analysis: Harmonic analysis is a mathematical technique used to decompose complex periodic functions into simpler components, often represented as sines and cosines. This method is crucial for understanding tidal forces and patterns, as it allows scientists to model and predict the behavior of tides based on various influencing factors such as the positions of the moon and sun, and the Earth's rotation.
Intertidal zone: The intertidal zone is the coastal area that is exposed to air during low tide and submerged under water during high tide. This unique environment is characterized by its dynamic conditions, which create a habitat where marine organisms must adapt to fluctuating levels of salinity, temperature, and moisture. These adaptations are crucial for survival, making the intertidal zone a rich area for studying the interaction between tidal forces and marine life.
Mean sea level: Mean sea level (MSL) is the average height of the ocean's surface, measured over a specific period and used as a baseline to determine elevation on land and water. It serves as a critical reference point for understanding tides, coastal processes, and sea-level rise, allowing scientists to track changes in ocean dynamics over time.
Mixed tides: Mixed tides refer to a tidal pattern characterized by the presence of both diurnal (one high tide and one low tide each lunar day) and semidiurnal (two high tides and two low tides each lunar day) tides within a single day. This results in variations in the height of the tides, with one high tide being noticeably higher or lower than the other. Mixed tides occur in areas where the gravitational forces from the moon and sun interact in complex ways, often influenced by geographical features and oceanic conditions.
Neap tide: A neap tide is a type of tide that occurs when the gravitational forces of the moon and sun are at right angles to each other, resulting in the lowest tidal range. During neap tides, the difference between high and low tides is minimized, leading to less extreme tidal movements. This phenomenon is closely related to the alignment of celestial bodies and plays a crucial role in understanding tidal patterns and forces in oceanography.
Newton's Law of Universal Gravitation: Newton's Law of Universal Gravitation states that every mass attracts every other mass in the universe with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers. This principle is crucial for understanding how celestial bodies, including Earth and the Moon, interact gravitationally, which is fundamental in explaining tidal forces and patterns.
Pierre-Simon Laplace: Pierre-Simon Laplace was a French mathematician and astronomer who made significant contributions to the fields of probability, statistics, and celestial mechanics in the late 18th and early 19th centuries. He is particularly known for his work on the mathematical theory of tides, where he explored how gravitational forces exerted by celestial bodies affect tidal patterns on Earth.
Satellite altimetry: Satellite altimetry is a remote sensing technique that uses satellites to measure the distance from the satellite to the ocean surface, allowing for the assessment of sea surface height and topography. This technology provides crucial data for understanding ocean dynamics, marine geology, and the Earth's climate system, as well as monitoring changes in sea level, which can be linked to global warming and tectonic activity.
Semidiurnal tides: Semidiurnal tides are a type of tidal pattern characterized by two high tides and two low tides occurring within a single lunar day, typically lasting about 24 hours and 50 minutes. This tidal cycle is influenced by the gravitational pull of the moon and the sun, as well as the geographical features of coastlines and ocean basins, leading to a regular rhythm in sea level changes.
Sir Isaac Newton: Sir Isaac Newton was a renowned English mathematician, physicist, and astronomer who is best known for his laws of motion and universal gravitation. His work laid the foundation for classical mechanics and greatly influenced our understanding of tidal forces and their patterns, making him a key figure in the study of oceanography and the behavior of tides.
Spring tide: A spring tide is a type of high and low tide that occurs when the Earth, the moon, and the sun are aligned in a straight line, resulting in the highest and lowest tidal ranges. This phenomenon typically happens during the full moon and new moon phases, leading to significant variations in sea levels and tidal forces, making them crucial for understanding tidal patterns.
Tidal Amplitude: Tidal amplitude refers to the height difference between the high tide and low tide levels in a specific coastal area. This measurement is crucial for understanding the intensity and variations of tides, which are primarily driven by the gravitational forces exerted by the moon and the sun. The tidal amplitude can vary significantly depending on geographical location, local topography, and the alignment of celestial bodies.
Tidal Cycle: A tidal cycle refers to the regular rise and fall of sea levels caused by the gravitational forces exerted by the moon and the sun on Earth's oceans. This cycle typically occurs in a pattern of two high tides and two low tides each day, influenced by the alignment of the Earth, moon, and sun. The timing and amplitude of tides can vary based on geographic location, the shape of coastlines, and other factors.
Tidal Range: Tidal range is the vertical difference in height between high tide and low tide at a specific location. This difference can vary significantly depending on various factors, including the alignment of the Earth, moon, and sun, as well as local geographical features. Understanding tidal range helps to explain tidal forces and patterns, as it provides insight into how these natural phenomena affect coastal environments and ecosystems.
Tidal wetlands: Tidal wetlands are coastal ecosystems that are influenced by the rise and fall of tides, consisting of salt marshes and mangrove swamps. These areas play a crucial role in protecting shorelines from erosion, providing habitat for wildlife, and filtering pollutants from water. The health and dynamics of tidal wetlands are closely tied to tidal forces and patterns, which shape their ecological functions and interactions with the surrounding environment.
Tide gauge: A tide gauge is an instrument used to measure the change in sea level relative to a datum, typically the land or a fixed reference point. These measurements are crucial for understanding tidal forces and patterns, as they help in observing how tides fluctuate due to gravitational pulls from celestial bodies and the influence of local geography.
Tide Tables: Tide tables are charts or schedules that provide predictions of the times and heights of tides at specific locations over a given period, usually spanning a month or a year. These tables are essential for understanding tidal patterns and tidal forces, as they allow individuals to anticipate tidal changes for activities such as fishing, boating, and coastal management.