Introduction
Tides are among the most observable natural phenomena. They consist of rhythmic rises and falls of sea level. These tides shape coastlines, feed marine life, and dictate human activity along shores. Most people recognize the daily oscillation between high and low tide. However, few people understand the planetary mechanics that drive this cycle.
This article unpacks the science of tides through a rigorous “Harvard framework” approach, encompassing:
- Explanation of key concepts
- Supporting evidence and examples
- Critical evaluation
- Implications for society and the environment
We draw on leading sources such as NASA, NOAA, and peer-reviewed scientific literature to substantiate our insights (NASA, 2022; NOAA, 2023).
1. The Core Physics: Gravity, Inertia and the Earth–Moon–Sun System
1.1 Gravitational Attraction and Tidal Bulges
Tides are primarily the result of gravitational interaction. As per Newton’s law of universal gravitation, any two masses attract each other. Although the Sun has greater mass, the Moon—despite being only 1/81 the mass of Earth—exerts a stronger tidal influence due to its proximity. This gravitational tug stretches Earth’s oceans into two tidal bulges: one on the side facing the Moon and another on the opposite side, caused by centrifugal force resulting from Earth-Moon rotation. When these bulges align with coastal areas, high tide occurs (Bikos et al., 2024).
1.2 The Sun’s Supporting Role
The Sun, though nearly 400 times farther from Earth than the Moon, still contributes about 46% of the Moon’s tidal force. When Earth, Moon, and Sun align—during full and new moons—their combined gravities create more pronounced tides (spring tides). Conversely, when the Moon is at a 90° angle to the Sun relative to Earth, neap tides (weaker tidal ranges) occur (NOAA, 2023).
1.3 Rotation and the Lunar Day
Earth completes a rotation every 24 hours relative to the Sun (solar day) but every 24 hours and 50 minutes relative to the Moon (lunar day). Consequently, the tidal cycle is not precisely 12 hours but closer to 12 hours and 25 minutes, producing two high and two low tides per lunar day (Doodson & Warburg, 2019).
2. Spring, Neap and Extreme Tides
2.1 Spring Tides: Gravitational Synergy
Twice each lunar month, during full and new moons, Earth, Moon, and Sun align—a condition known as syzygy. This alignment intensifies tidal forces, producing the highest high tides and the lowest lows—spring tides (Cheng, 2021).
2.2 Neap Tides: Gravitational Opposition
Approximately one week after a spring tide, the Moon reaches its first or last quarter phase. At these points, the Sun’s and Moon’s gravitational forces act at right angles, partially cancelling each other out. The result is neap tides, marked by minimal differences between high and low tide (Pugh & Woodworth, 2019).
2.3 Perigean and Apogean Effects
The Moon’s elliptical orbit causes variations in its distance from Earth. At perigee (closest approach), the Moon’s gravitational pull is stronger, leading to slightly more extreme spring tides—sometimes called “supermoons”—that may be 5–15% stronger than average. At apogee (furthest point), tidal extremes diminish (NASA, 2022).
3. Topography and Regional Variability
3.1 Continental Geometry and Ocean Basins
If Earth were a smooth sphere, open-ocean tidal amplitudes would be uniform (~1 meter). However, real-world conditions—continental placements, basin shapes, and seabed topography—distort these waves. For instance, the Bay of Fundy in Canada experiences the world’s highest tidal range at 16 meters, while the Mediterranean Sea often shows less than 40 centimeters (Cartwright, 2020; Pugh & Woodworth, 2019).
3.2 Resonance and Funnel Effects
Certain bays and fjords resonate with the natural frequency of tidal waves. When this resonance matches the tidal forcing frequency, amplification occurs. Norway’s fjords and the English Channel exhibit this effect, whereas closed seas like the Baltic show weak tidal ranges due to poor resonance (Cheng, 2021).
3.3 Tidal Currents and Straits
Where oceanic water is forced through narrow straits, tidal currents accelerate dramatically. Norway’s Saltstraumen, one of the world’s fastest tidal currents, exceeds 8 meters per second and generates intense whirlpools. Such features play vital roles in nutrient mixing and ecosystem dynamics but pose risks to navigation (Bikos et al., 2024).
4. Atmospheric Modulation: Weather and Storm Surge
4.1 Atmospheric Pressure
Barometric pressure influences sea level: a 1 hPa increase depresses sea level by about 1 cm. High-pressure zones can suppress tides, while low-pressure systems—often associated with storms—can elevate them (NOAA, 2023).
4.2 Wind Stress and Coastal Setup
Strong onshore winds can physically “pile” water against coastlines, a phenomenon known as storm surge. When such surges coincide with high spring tides or lunar perigee, the result—storm tide—can cause catastrophic flooding. Hurricane Katrina (2005) and Superstorm Sandy (2012) are textbook examples (FEMA, 2023).
5. Types of Tidal Regimes
- Semi-Diurnal: Two nearly equal high and low tides per lunar day (common on Atlantic coasts).
- Diurnal: One high and one low tide per lunar day (Gulf of Mexico, Java Sea).
- Mixed: A combination of both, with unequal highs and lows (Pacific and Indian Oceans) (Pugh & Woodworth, 2019).
6. Ecological and Societal Implications
6.1 Coastal Ecosystems
Tides structure intertidal zones that host biologically rich communities. Spring tides expand feeding habitats for shorebirds, while neap tides protect juvenile fish from predators. The cyclical immersion/exposure supports biodiversity from mangroves to mussels (Thompson et al., 2018).
6.2 Navigation and Shipping
Accurate tide tables are crucial for safe harbor operations, especially for large ships navigating shallow ports or under bridges. Historical maritime accidents often involved misjudged tidal windows (IMO, 2020).
6.3 Renewable Energy Potential
The predictability of tides makes them a valuable energy source. Tidal-stream and barrage systems, like France’s La Rance plant or the proposed Swansea Bay project in the UK, offer low-carbon energy solutions (IRENA, 2021).
7. Myths, Misconceptions and Human Biology
7.1 The “Lunar Effect” on Humans
Despite popular belief, the Moon’s gravitational force on individual humans is negligible—equivalent to the weight of a mosquito. Scientific reviews find no significant correlation between lunar phases and human behavior, though some studies suggest minor impacts on sleep cycles (Hough, 2019; Cajochen et al., 2013; Rotton & Kelly, 2022).
7.2 Werewolves and Folklore
Many cultures linked full moons with madness or supernatural transformations. These myths reflect humanity’s deep psychological and cultural ties to lunar rhythms, despite lacking scientific basis.
8. Forecasting and Measuring Tides
8.1 Tide Gauges and Satellites
Modern monitoring uses acoustic, radar, and satellite altimetry systems (e.g., Jason and TOPEX/Poseidon missions) to measure sea levels with millimeter precision (NASA, 2022).
8.2 Harmonic Analysis
Tidal predictions employ harmonic analysis, breaking sea-level signals into sinusoidal constituents (e.g., M2, S2, K1). The superposition of these allows accurate long-term forecasting (Doodson & Warburg, 2019).
9. Climate Change: A New Tidal Context
9.1 Sea-Level Rise
Global sea levels are rising at about 3.3 mm/year due to thermal expansion and melting ice sheets (IPCC, 2021). This elevates the baseline for high tides, increasing the flood risk even under regular conditions.
9.2 Changing Storm Patterns
Warming oceans intensify storm systems. The interaction of elevated sea levels with more potent storms could double or triple the frequency of extreme storm tides in many regions by 2100 (FEMA, 2023).
Conclusion
Tides are the result of a cosmic interplay between gravity, inertia, and planetary motion—a predictable ballet of celestial forces. Yet the expression of that ballet is shaped by Earth’s topography, atmospheric variability, and now, human-induced climate change. Understanding tidal dynamics is critical for coastal infrastructure, ecosystem conservation, maritime logistics, and the future of renewable energy. While myth and mystery still swirl around the Moon’s influence, the true story of tides is one of physics, mathematics, and the beautiful complexity of Earth’s systems.
Share this:
Discover more from Jarlhalla Group
Subscribe to get the latest posts sent to your email.