Tides Flashcards
Periodic raising and lowering of ocean sea level, occur daily, Newton’s gravitational laws explain relationship.
Tides
Tides were recognized even by early sailors as they associate ____ with full moon and new moon and _____ with quarter moon.
High tides, Low tides
In ____, Magellan set sail with 5 ships to find a western route to the much sought after _____ and ended up “discovering” the Philippine Islands.
1519, Spice Islands
First man to sail around the world was a Malay named _____?
Enrique of Malacca
_____, there was the biggest super tide in 18 years, which covered the causeway. The location was ____?
March 2016, Mont Saint Michel, Normandy in France
- Caused by gravitational attraction of Sun, Moon, and Earth
- Alternate rise and fall of sea level with an average period of 12.4h (24.8h in some places)
- Very long and regular _____ waves, Wavelengths on the order of thousands of kilometers, Heights up to 15m
Tides, Shallow-water
Average depth of ocean:
3.7 km
Theory would best describe tides on a completely water-covered Earth – so this is an idealized model for tide formation.
Equilibrium Theory of Tides
_____ takes into account the effect of continents, shallow water, and partially enclosed ocean basins on tide formation. This is a more realistic model of tides.
Dynamic Theory of Tides
Tide Generating Forces:
- Gravitational force between Moon and Earth
- Centripetal force caused by earth’s rotation
- Balance pointy center of mass, ~1700 km from the surface.
- Earth-moon system orbit around this center of mass as they orbit the sun.
Barycenter
Force that interconnects the sun, its planets, and their moons and keeps them in relatively fixed orbits.
Gravity
Every object that has mass in the universe is attracted to every other object. From this law, ____ is derived.
Newton’s Law of Universal Gravitation, Gravitational Force
Proportional to product of masses (as it ____ mass, force _____) and is inversely proportional to square of separation distance.
Gravitational Force, Increase, Increase
If distance ______ then gravitational force _____.
Increases, Decreases
Gravitational force is greatest at _____ (closest to moon) and least force is at _____ (furthest from moon and opposite zenith).
Zenith, Nadir
- Center-seeking force; rotation about “barycenter” or center of mass between two bodies in orbital motion.
- Tethers Earth and Moon to each other
- The _____ (the red arrows) is everywhere the same. The red arrows are all the same length and point in the same direction.
Centripetal Force
Mathematical differences between centripetal and gravitational forces.
Resultant Forces
Horizontal components of the resultant forces
Tide-generating forces
Result when force pushes water into two simultaneous bulges (one toward moon, and one away from moon).
Lunar Bulges
As earth rotates, it carries various locations into and out of ____ so that all points on its surface (except poles) experience __ high tides daily.
Bulges, Two
The Earth _____ underneath these bulges. Two high tides, ___ hours apart (also called _____, the time between high tides)
Rotates, 12, Tidal Period
Seawater moves on shore
High tide, flood tide
Seawater moves offshore
Low tide, ebb tide
Reason why tidal times change daily? Lunar day is ____ longer than solar day so high tides are 12 hours and 25 minutes apart.
50 minutes
Time that has elapsed between when moon is directly overhead and the next time the moon is directly overhead
Lunar Day
The Sun is much more massive than the Moon but much further away.
____ are ___ the size of lunar bulges.
Solar Bulges, 46%
Similar to lunar bulges but much smaller
Solar Bulges
New/full moon – tidal range greatest – _____ (lunar and solar bulges are in sync)
Spring Tide
Quarter moons – tidal range least – ____ (lunar and solar bulges are out of sync)
Neap Tide
Time between spring tides about _____.
Two Weeks
- _____ have the highest high tides and the lowest low tides
- Maximum difference between high and low tide
- Constrictive interference between lunar and solar bulges.
Spring Tides
- Have the lowest high tides and the highest low tides
- Minimum difference between high and low tide
- Destructive interference between lunar and solar bulges
Neap Tides
- Sun to Earth: 23.5o N or S of equator
- 5 degree tilt of moon’s path around Earth relative to Earth’s path around sun
Declination
- In total, Moon relative to Earth shifts up to 28.5o N or S of equator
- Shifts lunar and solar bulges from equator
- Unequal tides as earth spins through unequal size tide bulges for a given latitude
- What’s the cause?
Declination
Earth’s _____ leads to unequal tide ranges.
Tilted Axis
When earth is closest to moon. tidal range is great
Perigee
When Earth is furthest from moon, tidal range is least
Apogee
Perigee - Apogee = ____ days?
27.5 days
When Earth is closest to the sun, January, tidal range is greatest
Perihelion
When Earth is furthest from sun, July, tidal range is least.
Aphelion
Perigean full moon - ?
Supermoon
Moon experiences perigee ____ per orbit but not always coinciding with full Moon
Supermoon.
Once
Perihelion and Aphelion - difference between them amounts to ____, small enough to pass unnoticed. Earth’s orbit is very close to a circle.
3.3%
Refers to the straight-line configuration of three celestial bodies
Syzygy
Monthly Tidal Cycle
- ?
* New or Full moons
* Tidal range greatest
* Syzygy
Spring Tides
Monthly Tidal Cycle:
- ?
* Quarter moons
* Tidal Range least
* Quadrature
Neap Tides
Difference between high and low tide
Tidal Range
______ for a location remains the same throughout the year.
Tidal Pattern
____ show weekly switching of spring tide-neap tide cycle.
Tidal Curves
Spring Tide + Perigee
- Exceptionally high tidal range
- Every 1.5 years or so
- Results in flooding of low-lying coastal areas
- If storm occurs as same time, damage can be extreme
Proxigean Tides
One high tide/ one low tide per day
Diurnal
Two high tides/two low tides per day, tidal range about the same
Semidiurnal
Two high tides/two low tides per day, tidal range is different, most common
Mixed
- Common in shallow inland seas such as Gulf of Mexico and SE Asia
- Common along Atlantic coast of US
- Most common in the world, including Pacific coast of N America
- Diurnal
- Semi-diurnal
- Mixed
Water rushes up a bay or river with incoming tide
Flood Current
Water drains from bay or river as tide goes out
Ebb Current
Peak of each high tide with no current motion
High Slack Water
Peak of each low tide with no current motion
Low Slack Water
World’s largest tidal range
- A 258 km with wide opening to Atlantic Ocean. At northern tip, it splits into 2 narrow basins. At northern end of Minas Basin, spring tide range is 17m.
Bay of Fundy in Nova Scotia
True “Tidal Wave” in I rivers, Tide is channeled, low-gradient rivers, large tidal range
Tidal Bore
Tidal whirlpools in the Naruto Strait, a channel between Naruto in Tokushima and Awaji Island in Hyōgo, Japan.
Naruto Whirlpools
Effects of Tides on Day Length?
- Gravitational energy causing tides is dissipated as friction and is slowing the rotation of the Earth.
- Day length is increasing, but number of days per year is decreasing
350 million years ago, 22 hrs/day, there were ___ days per year. In 350 million years, ~ ___ hrs per day and ___ days per year
405 days per year, 26 hours a day, 320 days per year