The - rhythmic oscillation of the surface due to gravitational & centrifugal forces between the Earth, Moon and Sun. Tide-Generating Forces Equilibrium Tidal Theory tidal cycle – one low tide and one high tide consecutively Dynamic Tidal Theory diurnal tide - one low tide, one high tide a day Analysis of Tidal Signal semidiurnal tide – two tidal cycles daily; high and low tide levels are approximately equal semidiurnal mixed tide - same as semidiurnal except high and low tide levels vary

MTL = Mean Tide Level diurnal tide MHW = Mean High Water MLW = Mean Low Water semidiurnal tide MHHW = Mean Higher High Water MLLW = Mean Lower Low Water

– difference between MHW and MLW semidiurnal mixed tide

For navigation, the reference level is MLW or MLLW

Flood Tide: tide wave is propagating onshore water level is rising Ebb Tide: tide is moving out to water level is dropping Slack tide: period when tide wave is reversing low current velocity

1 Study of Tides Equilibrium Tidal Theory - ideal approach to understand basic principles Assumptions: 1: entire Earth surface covered in water 2: infinitely deep basin (no shoaling) 3: tidal bulge fixed relative to the moon universal law of gravitation Dynamic Tidal Analysis - realistic approach, studying the tides as 2 F= G m1 m2 / R they occur on earth, accounts for modification due to landmasses, G = universal gravitational constant geometry of ocean basins, earth’s rotation. A, B & C = gravitational forces m1, m2 = mass of bodies R = distance between centers of A’, B’ & C’ = centrifugal forces mass of bodies

The difference in force (for each unit mass of earth) between A, B & C = gravitational forces gravitational force of moon (or sun) and centrifugal force at an earth A’, B’ & C’ = centrifugal forces surface point is proportional to GM/R3

The Tidal Day = 24 hr 50 min

Lunar Orbit: the Earth – Moon system Diurnal = 24 hr 50 min has a period of 27.3 days Semidiurnal = 12 hr 25 min The Lunar Tide and how we get a ‘wave’

2 Declination Tide

Moon’s declination cycle 28.5N – 28.5S = 29.5 days Sun’s declination cycle 23.5N (summer solstice) – 23.5S (winter solstice) = annual

The Sun Tide Spring – Neap Cycle

Spring & Neap Spring Tide: greatest tidal range, Tides highest high tides and lowest low tides

Neap Tide: least tidal range, low high tides and high low tides

Lunar Cycle: the Earth – Moon system has a period of 29.5 days

Spring and Neap tides at two places on earth Orbital Influence on Tides

Astronomical High Tide: Moon at perigee, Sun at perihelion, and Earth- Moon-Sun system at syzygy (full or new moon)

3 Amphidromic Dynamic Tidal Analysis System Continents break up wave propagation Tide wave moves continuously around the globe only in the Southern Ocean (Antarctica). shallow-water wave: speed is controlled by depth of ocean Cotidal : oscillates because it is contained in ocean basins Lines reflected by continents, refracted by changes in depth, and diffracted (spread of energy sideways) as it passes through gaps affects the water movement because it is a large scale phenomenon

Co-range Lines

Bay of Fundy Tidal Resonance British Columbia 10 meter range

17m Tidal Range

4 Tidal Bores Tidal Resonance

Length = 110 miles Avg Depth = 78 feet

Shelf Width and Tidal Range Shelf Width and Tidal Range

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