Tide

Tide
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Name	Tide
Field	Oceanography
Related	Isaac Newton, Pierre-Simon Laplace, James Cook, Royal Navy (United Kingdom)

Tide

Tides are the periodic rise and fall of sea level observed along coasts and in enclosed basins, driven primarily by the gravitational interactions among the Moon, the Sun, and the Earth. They manifest as predictable cycles that influence navigation, fisheries, coastal engineering, and cultural practices across regions such as the Bay of Fundy, the North Sea, and the Pacific Ocean. The scientific explanation of tides was advanced by figures including Isaac Newton and formalized in mathematical treatments by Pierre-Simon Laplace; modern operational forecasting integrates observations from satellites like TOPEX/Poseidon and modeling centers such as the National Oceanic and Atmospheric Administration.

Overview

Tidal phenomena occur on coasts, estuaries, and in the open ocean, producing recognizable features like tidal ranges, tidal currents, and tidal bores in locales such as the Amazon River and the Severn Estuary. The interplay of celestial mechanics and terrestrial geography causes regional variations exemplified by semidiurnal tides in the Atlantic Ocean and diurnal tides near parts of the Gulf of Mexico. Longstanding institutions such as the Royal Observatory, Greenwich and the US Coast Survey contributed to tide measurement and charting critical to maritime powers including the British Empire and the United States Navy.

Causes and Mechanisms

Tidal forces originate from the differential gravitational pull of the Moon and the Sun on the Earth, modulated by the Earth's rotation and centrifugal effects in the Earth–Moon system described by Isaac Newton's law of universal gravitation. The dynamical theory advanced by Pierre-Simon Laplace introduced concepts such as tidal waves and forced oscillations; modern fluid dynamics employs the shallow water equations used by agencies like the National Oceanic and Atmospheric Administration and research groups at universities such as Scripps Institution of Oceanography. Resonance phenomena in enclosed seas like the Bay of Fundy amplify tidal ranges through natural oscillatory modes studied by researchers at institutions including the Woods Hole Oceanographic Institution.

Types and Patterns

Tidal regimes are classified by their periodicity: semidiurnal, diurnal, and mixed, with examples including the semidiurnal tides of the Atlantic Ocean coasts, diurnal tides in parts of the Gulf of Mexico, and mixed tides around the Pacific Northwest. Spring and neap tides arise from the syzygy and quadrature alignments of the Sun and Moon, while perigean and apogean effects relate to the Moon's elliptical orbit, with perigean spring tides contributing to extreme events observed historically at locations like the North Sea coast. Tidal bores, such as the one on the Qiantang River, manifest where funnel-shaped estuaries and strong tidal ranges interact, a subject of study by geomorphologists at the University of Cambridge and the University of California, Santa Cruz.

Measurement and Prediction

Tide gauges maintained by agencies such as the Permanent Service for Mean Sea Level and the National Oceanic and Atmospheric Administration provide long-term records used to compute harmonic constituents following methods established at the International Hydrographic Organization and the UK Hydrographic Office. Satellite altimetry missions including TOPEX/Poseidon, Jason-1, and CryoSat-2 complement in-situ observations, enabling global tide modeling by centers like the European Centre for Medium-Range Weather Forecasts and academic groups at the Massachusetts Institute of Technology. Numerical models incorporate tidal constituents, barotropic and baroclinic processes, and data assimilation techniques advanced by researchers at the National Centre for Atmospheric Research.

Ecological and Environmental Effects

Tides shape intertidal ecosystems such as salt marshes, mangroves, and mudflats found in regions including the Wadden Sea, the Gulf of California, and the Sundarbans. Tidal fluxes regulate nutrient exchange and habitat availability, influencing species assemblages studied by ecologists at the Smithsonian Institution and the Marine Biological Association. Tidal amplification and sea-level rise driven by climate change observed by the Intergovernmental Panel on Climate Change exacerbate coastal flooding risks in deltaic regions like the Ganges–Brahmaputra Delta and the Mississippi River Delta, prompting adaptation initiatives coordinated by agencies such as the United Nations Environment Programme.

Human Uses and Impacts

Humans have harnessed tidal energy through technologies ranging from traditional navigation techniques employed by explorers like James Cook to modern tidal barrages and turbines deployed in projects in the Rance River and proposed in the Severn Estuary. Coastal infrastructure—ports, seawalls, and tidal gates—constructed by authorities including the Port of Rotterdam Authority and municipal governments must account for tidal regimes and storm surge interactions exemplified by historical events like the North Sea flood of 1953. Urban planning in littoral cities such as Tokyo, New York City, and London increasingly integrates tidal predictions produced by national meteorological services like the Met Office.

Cultural and Historical Significance

Tides have informed calendars, myths, and maritime law across civilizations including the Polynesian navigation traditions, the maritime jurisprudence codified in the Rule of the Road at Sea, and coastal rituals of communities along the Bay of Bengal. Literary and artistic works referencing tidal imagery include creations by authors and institutions such as William Wordsworth and the Royal Academy of Arts. Historical developments in tidal science influenced navigation and hydrography during the age of sail under figures like James Cook and imperial administrations such as the British Admiralty, shaping trade routes and colonial expansion.

Category:Oceanography