NOTES
Links to summaries of key issues for each topic
VISUALS
Links to images employed in lectures on a topic-by-topic basis
TEXT
Link to chapter outlines at online learning center at McGraw Hill.
NOTES
Links to summaries of key issues for each topic
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Notes on Topic:
The notes represent summaries
of key issues for each topic
They emphasize the terminology used to
describe the various phenomena.
| 2. Tide Patterns, Levels and Tidal Currents: |
| Learning Objectives: |
- Comprehension of the features, causes and behavior of ocean tides
- Understanding of the variability in tidal characteristics
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| Tide Patterns: |
- Dependent on number of high and low tides per day and their heights
- Diurnal (daily):
- 1 high and 1 low tide/day
- Semi-diurnal (semi-daily):
- 2 high and 2 low tide/day of equal height
- Semi-diurnal mixed tides:
- 2 high, 2 low tide/day of unequal height
- higher and lower high water (HHW, LHW)
- lower and higher low water (LLW, LHW)
- Long-term measurements give average (or mean) tidal level.
- Charted depths relative to tidal datum (typically mean low water)
- minus tides can occur when tide falls below tidal datum.
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| Tidal Currents: |
- Rising tides (rising water level): flood tide;
- Falling tides: ebb tides
- Tidal currents: related to flood and ebb of tide
- slack water as tide turns from flood to ebb or vice versa
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| 3. Equilibrium Tidal Theory: |
| Learning Objectives: |
- Appreciation of combination of gravitational factors that affect tides
- Understanding of the tidal influences of the Moon and Sun
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| Tidal Forces: |
- Tides analyzed according to:
- laws of physics: equilibrium tidal theory
- by observation: dynamic tidal analysis, separates different factors
- Balance of gravitational attraction and centrifugal forces
- gravitational attraction:
- greater on the Earth's side that faces the Moon
- centrifugal forces:
- uniform on surface
- forces are vectors with magnitude and direction
- forces separated into vertical and horizontal components
- vertical force countered by Earth's gravity
- horizontal force causes tides
- creates egg-shaded water envelope
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| Influences on Tideal Characteristics: |
- Moon Tide:
- high tides when Moon overhead or at opposition
- distorts Earth's water envelope creating bulges.
- Tidal Day:
- 24h 50min, based on progression of Moon's orbit relative to Earth's
rotation.
- Tide Wave:
- Moon produces tide wave
- crest = high water, trough = low water (a shallow water wave).
- Sun Tide:
- effect of Sun's gravity similar to Moon, but weaker (~46% of Moon)
- hence effects subordinate to those of the Moon.
- Spring Tide and Neap Tide:
- Spring and neap tides caused by combination and counteraction of gravitation
attraction of Sun and Moon
- spring tides, greatest tidal range at full, new moon
- neap tides, lowest tidal range at 1st, 3rd quarters
- Declinational Tides:
- Moon position changes monthly from 28.5°N to 28.5°S
- affects latitude of tidal bulge, known as declinational tide
- similarly, Sun's position varies 23.5°N to 23.5°S in a year.
- Elliptical Orbits:
- Tides affected by variations in Earth-Moon distance
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Department of Geological Sciences,
1001 E. Tenth Street, Bloomington, IN 47405-1403
Phone: (812) 855-5582 Last updated: 7 December 2000
Comments: simon@indiana.edu
Copyright
2000, The Trustees of Indiana University
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