3.1 Tidal Phenomena and Driving Forces

Tides are driven by gravitational forces from the Moon and Sun, with the Moon's influence being stronger due to its proximity. These forces create complex patterns of high and low tides, varying in timing and magnitude based on celestial positions and Earth's rotation.

Tidal patterns can be semidiurnal, diurnal, or mixed, influenced by factors like latitude and coastline shape. Spring and neap tides occur due to Moon-Sun alignments, while tidal analysis uses harmonic components to predict future tides accurately.

Astronomical Influences

Gravitational Forces and Celestial Bodies

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• Tides primarily driven by gravitational forces exerted by the Moon and Sun on Earth's oceans
• Moon's gravitational pull has a stronger influence on tides due to its proximity to Earth compared to the Sun
• Gravitational force varies inversely with the square of the distance between two objects, explaining the Moon's dominant role in tidal phenomena
• Sun's gravitational force on Earth's oceans is about 46% that of the Moon, still significant in shaping tidal patterns

Lunar Cycles and Tidal Variations

• Lunar cycles, particularly the lunar month (29.5 days), strongly influence tidal patterns
• Moon's orbital position relative to Earth and Sun determines the timing and magnitude of tides
• Lunar phases (new moon, first quarter, full moon, last quarter) affect tidal ranges
• Lunar declination, the Moon's position above or below Earth's equator, influences diurnal inequality in tidal heights

Coriolis Effect on Tidal Currents

• Earth's rotation produces the Coriolis effect, deflecting moving objects to the right in the Northern Hemisphere and left in the Southern Hemisphere
• Coriolis force affects tidal currents, causing them to rotate clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere
• Coriolis effect influences the formation of tidal gyres and amphidromic systems
• Magnitude of the Coriolis force depends on latitude, with stronger effects at higher latitudes and negligible impact near the equator

Tidal Patterns

Semidiurnal and Diurnal Tides

• Semidiurnal tides exhibit two high tides and two low tides of approximately equal height each lunar day (24 hours and 50 minutes)
• Diurnal tides feature one high tide and one low tide per lunar day, with significant differences in height between successive high or low tides
• Tidal pattern at a location depends on its latitude and the shape of the coastline or basin
• Mixed semidiurnal tides occur in areas with unequal heights of the two high tides or two low tides in a lunar day

Spring and Neap Tides

• Spring tides occur during new moon and full moon phases when Earth, Moon, and Sun align, resulting in higher than average tidal ranges
• Neap tides happen during first quarter and last quarter phases when Moon and Sun are at right angles to Earth, leading to lower than average tidal ranges
• Tidal range is the difference in height between high tide and low tide, with spring tides having larger ranges than neap tides
• Spring and neap tides alternate approximately every 7.4 days (half a lunar cycle) due to the changing relative positions of Earth, Moon, and Sun

Tidal Analysis

Tidal Constituents and Harmonic Analysis

• Tidal constituents are the individual harmonic components that make up the complex tidal pattern at a given location
• Each constituent represents a specific astronomical or hydrodynamic factor influencing the tides (lunar semidiurnal, solar semidiurnal, lunar diurnal)
• Tidal constituents have unique periods, amplitudes, and phases determined by the motions of Earth, Moon, and Sun
• Harmonic analysis is a mathematical technique used to decompose a tidal record into its constituent components, enabling accurate tidal predictions

Tidal Prediction and Modeling

• Tidal prediction involves forecasting future tidal heights and currents based on the understanding of tidal constituents and their interactions
• Tidal models use mathematical equations and numerical methods to simulate tidal dynamics in coastal and oceanic regions
• Accurate tidal predictions are essential for various applications (navigation, coastal engineering, renewable energy)
• Tidal analysis and prediction consider factors such as bathymetry, coastline geometry, and meteorological conditions in addition to astronomical forces