Tides - 9 Flashcards
What is high tide?
The crest of the waveform
What is low tide?
The trough of the waveform
What is the tidal range?
The vertical range between high and low tide
What is the tidal period?
The time between consecutive high or low tides
What is a semidiurnal tide?
Two high and two low tides with a similar tidal range per day. The tidal period is 12 hours 25 minutes
What is a diurnal tide?
One high and one low tide each day with a similar tidal range. The tidal period is 24 hours 50 minutes
What is a mixed tide?
Two high and two low tides per day with dissimilar tidal ranges
What are the different types of tides?
- Diurnal
- Semidiurnal
- Mixed
What are the two types of tides?
- Spring tides
- Neap tides
What are spring tides?
The two tides that occur each month with the largest tidal range
What are neap tides?
The two tides that occur each month with the smallest tidal range
What two forces generate tides?
Gravitational attraction and centrifugal force
How does gravitational force vary?
- Directly with the mass of the interacting bodies
- Inversely with the square of the distance separating them
How much more force does the Moon exert compared to the sun?
Twice the gravitational attraction and tide-generating force as the sun
What affect does gravitational force have on the oceans?
It pulls the ocean toward the moon and the sun, creating two gravitational tidal bulges
What effect does the centrifugal force have on the oceans?
This force pushes outward from the sun, creating a tidal bug on the side of the earth facing away from the sun.
What is the barycentre?
The centre of mass between the earth and the moon
What is declination?
The angle between the earth’s axis and the lunar and solar orbital plane
What affect does declination have on tidal bulges?
It determines the latitude of these tidal bulges
How do tidal bulges generate tides?
As the earth rotates, a point on the earths surface passes through these bulges, creating the high and low tides
How often does the moon go around the earth?
27.3 days
When do spring tides occur?
When the earth, moon and sun are aligned and the tidal bulges demonstrate constructive interference (coincides with the new and full moon)
When do neap tides occur?
When the earth, moon and sun form a right angle with one another and the tidal bulges demonstrate destructive interference (coincides with the first quarter and last quarter moon)
What causes tides to occur 50 minutes later each day?
- The earth and the moon both rotate from west to east
- By the time the point on the earth’s surface that was directly below the moon has completed one rotation, the moon has advanced its orbit, an additional 50 minutes of earth rotation is required before that point is directly below the moon again
How are the movement of tides across ocean basins altered?
- deflected by Coriolis
- blocked by landmasses
What is an amphidromic system?
A rotary standing wave in which the wave progresses about a node, with the antinode rotating about the basins edges
What are cotidal lines?
Lines that connect points on the rotary wave that experience high tide at the same time
Are cotidal line evenly spaced?
No - tides are shallow water waves and their celerity depends on water depth
What are corange circles?
Line connecting points together that experience the same tidal range. They form irregular circles that connect about the node
How many components influence tides?
65
In what conditions can tides not rotate?
Long, narrow basins (tides instead reverse, flowing in and out)
When does tidal resonance occur?
When the period of the basin is similar to the tidal period
What is a flood current?
The flow of water toward the land with the developing high tide
What is an ebb current?
The flow of water away from the land with the developing low tide
What is an internal tide?
An underwater wave the pulsates with the tides that control the inclinations of the continental slope through erosion
What is a tidal bore?
A wall of water that surges upriver with the advancing high tide
Under what conditions do tidal bores occur?
- Tidal range is larger than 5 metres
- River valley tapers headward
- Water depth systematically decreases upstream
When can power be generated from tides?
If the tidal range is greater than 5 metres in a large bay connected to the ocean by a narrow opening
