Tides

Tidal Wave Form Differ from other waves because caused by the interactions between the ocean, Sun and Moon Crest of the wave form is high tide and trough is low tide

Tidal Wave Form Tidal Range = Vertical difference Tidal period = time between consecutive high or low tides

Tidal Range Over a month the daily tidal ranges vary systematically with the cycle of the Moon. Also altered by shape of basin & sea floor

Measuring Tidal Range Tide gauges automatically record tidal fluctuations Satellites pick up data, post on internet

Gravitational Force Gravity varies directly with mass, but inversely with distance

Gravitational Force Moon exerts twice the gravitational attraction and tide-generating force as the Sun - WHY???

Centrifugal Force The push outward from the center of rotation

Gravitational Attraction Pulls ocean towards Moon & Sun, creating two gravitational tidal bulges

Centrifugal Force Centrifugal force makes water slosh away from the Earth on the exact opposite side that the moon's gravity is pulling on

Spring Tides Earth, Moon & Sun aligned in a straight line (New moon & full moon) Tidal bulges display constructive interference, producing very high, high tides and very low, low tides.

Neap Tides Earth, Moon and Sun aligned at right angles (1st & 3rd quarter moon) Display destructive interference, producing low high tides and high low tides.

Tide Cycles

Seasonal Tides Latitude of the tidal bulges is determined by tilt in Earth’s axis

Seasonal Tides Moon cycle does not exactly match Earth’s rotational cycle Causes tides to occur 50 min later each day

Monthly Tide Patterns

Movement of tides Deflected by Coriolis Blocked by continental landmasses Forms a rotary wave

Movement of tides Semidiurnal - 2 cycles of even heights Mixed - 2 cycles of uneven heights

Movement of tides Diurnal - one cycle per day

Basins Tidal ranges increase if a bay tapers landward because water is funneled towards the basin’s narrow end

Tidal Bore A wall of water that surges upriver with the advancing high tide

Bay of Fundy World’s largest tidal range Up to 10m per day

Tidal Currents Movement of water high and low tides towards and away from land, generates tidal currents Flow Tide = flow of water towards the land Ebb Tide = flow of water away from the land Slack Tide - Interval between tides

Tide-Dependent Animals

Grunion Dependent on tides Spawn 2-3 days after highest tide

Grunion Up to 12 inches: bait fish but tasty Must be caught BY HAND (slippery) Needs fishing license 16yrs or older Courtesy of Chris Oakamoto

Daytime Spawn in Mexico Courtesy of Chris Oakamoto

Grunion Males surround females as they lay eggs 8-10” deep Courtesy of Chris Oakamoto

Grunion “Milt” (sperm) seeps down to fertilize eggs. Hatch in 10 days, at next high tide Courtesy of Chris Oakamoto

Sea Turtles Dependent on tides Females come ashore, dig nests

Sea Turtles Young hatch at night in warm sand Follow moonlight to water

Harnessing Tides Electricity generated from tidal currents Only when tidal range is >5 m in a large bay connected to the ocean by a narrow opening.

Harnessing Tides Dam constructed across opening Tide is allowed to flow into and out of bay when sufficient hydraulic head exist to drive turbines and generate power

Pro’s If turbines work in both directions, energy generated 4 times a day All advantages of normal hydroelectric power

Con’s Few suitable locations Needs shallow, narrow inlet to form a tidal bore: Bay of Fundy High cost of construction Environmental impacts Estuary degradation Fish chewed up in turbines

Designed by Anne F. Maben These images are for viewing only and may not be published in any form