geosc040, lecture 23. tides: sun, moon, rise and fall and sealevel changes
TRANSCRIPT
Geosc040, Lecture 23. Tides: Sun, Moon, Rise and Fall
and Sealevel Changes
Do you find yourself dreaming about the ocean?
Join the Marine Science Society!! (MSS)Meeting Time: Bi-weekly, Thursday at 6 pm in 103 Ferguson
Next meeting: April 17th For more information email Meredith Fish at: [email protected]
Check out our Facebook page: Penn State Marine Science Society
http://www.cpa.psu.edu/news/candy-wrapper-collection-2013%E2%80%932014
Read Chapter 9!
Check it out!Course web site:
Apr 15, 2014 Total Lunar Eclipse
Sargasso Sea Tribute & Declaration
Quiz 2: On Apr. 14
OLA 11 Due today, Thursday, 10 Apr
Homework 4 due Apr. 22http://www3.geosc.psu.edu/geosc040/Syllabus.html
Extra Credit Letter Grades will be posted by ~Apr 24
http://vimeo.com/89868953
North Atlantic stock: spawn in Sargasso Sea then larvae migrate to freshwater
Spawning Behavior• Catadromous vs. Anadromous Fishes
– anadromous, lit. means ‘running upward’– ”down-wandering” vs. “up-wandering” to spawn– eels--catadromous
• Salmon, shad, herring, striped bass, etc. are anadromous. They migrate from saltwater to freshwater to spawn
• Think about how they must “switch over” in fluid regulation• Note: Pacific salmon shrink and resorb their intestinal system when
they are about to spawn (they die shortly after spawning, of course)
Shad
Anadromous Fish
Origin of TidesTwo Approaches
1) Equilibrium theory. Makes simplifying assumptions, provides a basic understanding of tides
2) Dynamic theory. Complexities of coastlines, bays, ocean basin geometry, Earth deformation.
Fig 10.13
Fig 10.14Global Distribution of Tide Types
Note dominance of Semidiurnal tides
Tidal Regimes Macrotidal
Mont St. Michel, France
Why are there Two Tidal Bulges!-Gravity and Inertia (centrifugal force)
Gravity
Inertia
Why are there Two Tidal Bulges!-Gravity and Inertia (centrifugal force)
http://www.fearofphysics.com/SunMoon/sunmoon1.html
Why are there Two Tidal Bulges!-Gravity and Inertia (centrifugal force)
Fig 10.12
Basic elements of tidal variation over one month
Note Asymmetry in highs and lows
Note Asymmetry in highs and lows
A Higher High Tide
Lower High Tide
Timing and Predictability of Tides• Semidiurnal tides have a range that cycles over a 14 day period. • This coincides with the moon’s 28 day orbital period.• Monthly inequality• Max semi-diurnal tides occur when spring tides coincide with lunar perigee.
Predicting tides is difficult Factors to consider:
• lunar distance• solar distance• lunar declination• solar apparent declination• relative alignment of sun
and moon• coastal morphology• location of amphidromic
point• must also take into account
storms, wind patterns, etc.
This shows a situation when ______ occur, which is the time of the month when tides are ______…
A. Spring Tides, Largest because the Sun and Moon act togetherB. Spring Tides, Smallest because the Sun and Moon act in opposite
directionsC. Neap Tides, Smallest because the Sun and Moon act in opposite
directionsD. Neap Tides, Largest because the Sun and Moon act together
A. This diagram shows the time of the month when tides have largest amplitude (spring tides).
B. This diagram shows the time of the month when tides are smallest amplitude (neap tides).
C. Centrifugal forces play a role in creating ocean tides.D. The Earth-Moon system revolves around a point that is within
EarthE. All but A
Which of the following are true
Timing and Predictability of Tides• Semidiurnal tides have a range that cycles over a 14 day period. • This coincides with the moon’s 28 day orbital period.• Monthly inequality• Max semi-diurnal tides occur when spring tides coincide with lunar perigee.
Predicting tides is difficult Factors to consider:
• lunar distance• solar distance• lunar declination• solar apparent declination• relative alignment of sun
and moon• coastal morphology• location of amphidromic
point• must also take into account
storms, wind patterns, etc.
Variations in tidal amplitude
• Moon’s orbit around Earth is elliptical (eccentricity ~0.055)
Apogee (farthest ~0.40x106 km)
Perigee (closest ~0.36x106 km)
• Difference (4 x104 km) is important because gravitational attraction is proportional to square of distance
• Declination of lunar orbit varies 28.5 degrees above and below equator during lunar month
ApogeePerigee
Note that the Spring Tide during days 22 through 26 is bigger than the Spring Tide during days 6-8.
ApogeePerigee
• Max semi-diurnal tides occur when spring tides coincide with lunar perigee.
• Moon’s orbit around Earth is elliptical
Apogee (farthest ~0.40x106 km)
Perigee (closest ~0.36x106 km)
The tidal bulges on Earth:A. Are fixed relative to Earth’s surface, so they rotate 360° during a
day just like everything on EarthB. Make half a revolution each day, which is why there are two
bulges.C. Rotate from the north pole to the south pole and back every 24
hours.D. Are always directly over the equator.E. none of the above
The tidal bulges on Earth:A. Are fixed relative to Earth’s surface, so they rotate 360° during a
day just like everything on EarthB. Make half a revolution each day, which is why there are two
bulges.C. Rotate from the north pole to the south pole and back every 24
hours.D. Are always directly over the equator.E. none of the above• The tidal bulges are
‘stationary’ relative to the position of the moon and sun
• Points on Earth’s surface rotate under the high-tide bulges and low tide regions
The tidal bulges on Earth:A. Are fixed relative to Earth’s surface, so they rotate 360° during a
day just like everything on EarthB. Make half a revolution each day, which is why there are two
bulges.C. Rotate from the north pole to the south pole and back every 24
hours.D. Are always directly over the equator.E. none of the above
The Spring Tide during days 22 through 26 is bigger than the Spring Tide during days 6-8. What could explain this?
A) The Sun is closer to the moon
B) The moon is closer to Earth
C) Earth is spinning faster then
D) Tides are always larger at new moon
• Semidiurnal tides have a range that cycles over a 14 day period.
• This coincides with the moon’s 28 day orbital period.
• Max semi-diurnal tides occur when spring tides coincide with lunar perigee.
The Spring Tide during days 22 through 26 is bigger than the Spring Tide during days 6-8. What could explain this?
A) The Sun is closer to the moon
B) The moon is closer to Earth
C) Earth is spinning faster then
D) Tides are always larger at new moon
ApogeePerigee
• Max semi-diurnal tides occur when spring tides coincide with lunar perigee.
Diurnal and semi-diurnal Variations in tidal amplitude
Note that high tides are not always of equal amplitude. Which of the following are true?
A) Point x in the figure could have this tidal record
B) The difference (asymmetry) in high tides would be larger for points at higher latitude than point x
C) Tides are always larger at new moon
D) A and B
x
Note that high tides are not always of equal amplitude. Which of the following are true?
A) Point x in the figure could have this tidal record
B) The difference (asymmetry) in high tides would be larger for points at higher latitude than point x
C) Tides are always larger at new moon
D) A and B x
Origin of TidesTwo Approaches
1) Equilibrium theory. Makes simplifying assumptions, provides a basic understanding of tides
2) Dynamic theory. Complexities of coastlines, bays, ocean basin geometry, Earth deformation.
Dynamic theory of Tides and Amphidromic points
Continental margins and the Coriolis effect
1) Continents. As Earth spins the tidal bulges attempt to stay below the moon and opposite of it. Therefore water is forced against the continental margin.
•This occurs on the western margin of the ocean basin (eastern margin of continent)
Dynamic theory of Tides and Amphidromic points
Continental margins and the Coriolis effect
1) Continents. As Earth spins the tidal bulges attempt to stay below the moon and opposite of it. Therefore water is forced against the continental margin.
•This occurs on the western margin of the ocean basin (eastern margin of continent)
• Tides are very long-wavelength shallow water waves.
• Tidal crests are separated by half of Earth’s circumference!
• Picture waves trapped in ocean basins between continents.
2) Coriolis. In the northern hemisphere, as water travels north it moves to the right and thus the Eastern side of the ocean basin. The opposite happens for water traveling south.
•This sets up a counterclockwise wave motion, with water sloshing back and forth in the ocean basins.
Dynamic theory of Tides and Amphidromic points
1) Continents. As Earth spins the tidal bulges attempt to stay below the moon and opposite of it. Therefore water is forced against the continental margin.
•This occurs on the western margin of the ocean basin (eastern margin of continent)
• Tides are very long-wavelength shallow water waves.
• Tidal crests are separated by half of Earth’s circumference!
• Picture waves trapped in ocean basins between continents.
Dynamic theory of Tides and Amphidromic points
Continental margins and the Coriolis effect
Development of Amphidromic Circulation
Dynamic theory of Tides and Amphidromic points
Continental margins and the Coriolis effect
Development of Amphidromic Circulation
Amphidromic CirculationTidal crests move in a
counter-clockwise pattern around the basins of the northern hemisphere.
Like Fig 10.17
Noon
3 pm
6 pm
9 pm
Development of Amphidromic CirculationTidal crests move in a
counter-clockwise pattern around the basins of the northern hemisphere.
These rotary waves revolve around a fixed NODE (which experiences no tidal fluctuation-an amphidromic point).
The resulting circulation is called an amphidromic system.
Amphidromic Circulation and Tides
Amphidromic Circulation
These rotary waves revolve around a fixed NODE (which experiences no tidal fluctuation-an amphidromic point).
The resulting circulation is called an amphidromic system.
Tidal crests move in a counter-clockwise pattern around the basins of the northern hemisphere.
The tidal range toward the center of an amphidromic system is ____ the range at the edges of the system.
A. of longer duration thanB. larger thanC. about the same asD. smaller thanE. none of the above.
Development of Amphidromic CirculationTidal crests move in a
counter-clockwise pattern around the basins of the northern hemisphere.
These rotary waves revolve around a fixed NODE (which experiences no tidal fluctuation-an amphidromic point).
The resulting circulation is called an amphidromic system.
Amphidromic Circulation
Earth has about 12 amphidromic systems
• Tidal amplitude increases progressively away from amphidromic points
Fig 10.16
The dynamic theory of tidesA. Accounts for ocean basin geometry and continentsB. Predicts that tides move as shallow water wavesC. Accounts for the Coriolis effectD. All of the aboveE. None of the above
For an amphidromic system such as shown, if there is a high tide at B, there will be a high tide at A roughly
A. 12 hours laterB. 2 hours laterC. 6 hours laterD. At the same timeE. 3 hours later
B
A
Assume a semi-diurnal system
For an amphidromic system such as shown, if there is a high tide at B, there will be a high tide at B roughly
A. 12 hours laterB. 2 hours laterC. 6 hours laterD. At the same timeE. 3 hours later
B
A
Assume a semi-diurnal system
Tides are shallow water waves, produced by gravity and inertial (centrifugal) forces
A tide is a “forced” wave, and actually must travel very rapidly to keep up with the forcing (forcing is as fast as 1600 km/hr. at equator)
Earth-Moon Rotation AxisREVIEW
Dynamic theory of Tides. Complexities of coastlines, bays, ocean basin geometry, Earth deformation.