Quiz Nov 19 Flashcards
What are tsunamis and seismic sea waves caused by?
caused by water displacement
Tsunami
Long-wavelength (up to 200km)
shallow-water, progressive waves caused by the rapid displacement of ocean water
They can move at speeds over 800 km/h
Can reach a height of up to 30 meters
Seismic sea waves
Tsunami generated by sudden, vertical movement of earth along faults
What are the longest ocean waves?
Tides
Newton’s Law of Universal Gravitation
All objects attract each other with a force of gravitational attraction. Gravity
is universal. This force of gravitational attraction is directly dependent upon the masses of both objects and inversely proportional to the square of the distance that separates their centers.
Black hole
A body with immense mass, so big that not even the light escapes of it ́s gravity
Tides
Periodic, short-term changes in the height of the ocean surface at a particular place. Their wavelength can equal half of Earth’s circumference
what are tides caused by
They are caused by a combination of the gravitational force of the moon and sun and the motion of Earth
gravity and inertia
The equilibrium theory/model of tides
explains the tides based on the gravity and inertia generated by the position and attraction of Earth, moon and sun.
Does not factor the ocean depth or the position of land masses.
Assumes (wrong) that:
1) The sea floor does not influence the tides.
2) The ocean conforms instantly to the forces that affect the position of its surface.
3) The ocean surface is presumed to be in equilibrium with the forces acting on it.
In the equilibrium model:
• Gravity and inertia (centrifugal force):
gravity pulls the Earth and the moon towards each other, but inertia keeps them apart.
- In the equilibrium model:
* The moon?
does not revolve around the center of the Earth
• Rather, the Earth moon system revolves once a month around the systems center of mass, located 1650 km inside the Earth
The moon’s gravity?
The moon ́s gravity attracts the ocean surface towards the moon = first tidal bulge
Earths motion causing second bulge. how?
Earth ́s motion around the center of mass of the Earth-moon system throws
a bulge in the opposite side of Earth (Inertia) = second tidal bulge • The result are 2 tidal bulges
High tide
the crest of the planet-sized waves formed by the attraction of moon ́s gravity in equilibrium with inertia (every 6 hours approx.)
Low tide
the troughs of the planet-sized waves formed by the attraction of moon ́s gravity in equilibrium with inertia (every 6 hours approx.)
What influences the tides
both sun and moon
spring tides
caused by the linear alignment of the sun, Earth and moon. High tides are very high, low tides are very low, corresponding to full and new moons
neap tides
occur when the moon, Earth and sun form a right (90o) angle. High tides are not very high, low tides are not very low
The dynamic theory of tides
Explains the difference between observed tide behavior (2 m tide variation in average) and predictions based on the equilibrium theory (lunar tide = 55 cm; solar tide = 24 cm). Considers that: 1) Ocean surface never comes to equilibrium: Sun and moon change positions so rapidly that the water cannot keep up with their “movement”. 2) Tidal crest velocity is determined by ocean depth because the ocean is shallower than half of its wavelength. 3) As Earth turns, continents obstruct tidal crests
• Astronomical tide
tides caused by inertia and gravitational force of moon and sun
• Meteorological tide
variation of tide height caused by a storm (storm surge)
semidiurnal tides
two high tides and two low tides of nearly equal level each lunar day
diurnal (daily) tides
one high, one low
Semidiurnal/mixed tidal pattern
when successive high or low tides are of significantly different heights throughout the cycle (diurnal+semidiurnal tides)
Amphidromic points (AP)
No-tide points at the ocean around which the tidal crest rotates through one tidal cycle (counterclockwise in N Hemisphere, clockwise in S Hemisphere)
Tidal range
the height difference between high and low tides
In a narrow and restricted basin…
tide crest cannot rotate around an AP and water simply moves in and out of the bay
tidal bore
forms in some inlets exposed to great tidal fluctuation
Tidal currents in bays and harbors
FES
- Flood current — tide crest into enclosed area rising sea level
- Ebb current — tide trough – water rushing out of the enclosed area
- Slack water — a time of no currents
How are tides predicted
Study of past records permits prediction of tidal height to an accuracy of about 3 centimeters (1.2 inches) for years in advance.
Tidal datum
reference level to which tidal height is compared.
king tides
Spring tides are greater in the Northern Hemisphere in winter than in the summer, because Earth is closest to the sun.
tidal range
the height difference between high and low tides.
Increases with the distance from an amphidromic point. Largest in ocean basins. Extreme tides: 15 m
Why the Caribbean doesn ́t have such great tides?
not so much topography to alter the way the tidal bulge is distributed.
Channels between island will routinely see higher currents than surrounding areas because more water has to get between the islands to normalize the height
How long does the rotation of the sun take?
1 year
