Chapter 10: Tides

1
Chapter 10 Tides
Fig. 10-6
Fig. 10-7
2
Tide-producing forces

• Gravity and
• motions among
• Earth, Moon,
• and Sun

Fig. 10-2
3

• Centripetal force tethers Moon to Earth
• Directed away from barycenter

Fig. 10-4 a,b
4
Resultant tidal forces

• Gravitational force, Earth and Moon
• Centripetal force, Earth and Moon
• Resultant force moves ocean water horizontally

Fig. 10-6
Fig. 10-7
5
Tidal bulges

• Two equal and opposite tidal bulges
• Earth rotates beneath tidal bulges
• Two high tides
• Two low tides
• Per day

Fig. 10-8
6
Complications to simplest equilibrium theory

• Oceans do not cover entire Earth
• Oceans do not have uniform depth
• Friction between ocean and seafloor
• Continents
• Moon not always in same place with respect to
  Earth
• Lunar day longer than solar day

7
Lunar day

• Moon revolves around Earth
• Earth has to catch up with Moon to reach same
  position

Fig. 10-9
8

• Time between successive high tides shifts day
  after day
• Moon rises later each successive night

9
Solar tidal bulges

• Tide-producing force of Sun less than half of
  Moons
• Sun much farther away

10
Month tidal cycle

• Spring tides
• New Moon, Full Moon
• Earth, Moon, Sun syzygy
• Higher than usual high tides

Fig. 10-12
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• Neap tide
• First Quarter, Last Quarter
• Earth, Moon, Sun quadrature
• Lower than usual high tide

Fig. 10-12
12
Declination of Sun and Moon

• Orientation of Sun, Moon to Earths equator
• Sun 23.5o N and S, yearly cycle
• Moon 28.5o N and S, monthly cycle
• Unequal tides
• Successive tides different tidal range

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Unequal tidal range
Fig. 10-15
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Elliptical orbits

• Perigee
• Lunar tidal force greater
• Higher high tides
• Apogee
• Lunar tidal force lesser
• Lower high tides

Fig. 10-16
15
Dynamic theory of tides

• Tide shallow-water wave
• Speed varies with depth
• Lags behind Earths rotation
• Rotary flow in open ocean basins
• Amphidromic point
• Cotidal lines

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Rotary flow

• Crest (high tide) rotates
• Counterclockwise in Northern Hemisphere
• Clockwise in Southern Hemisphere

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Tidal patterns

• Diurnal
• One high, one low tide per lunar day
• Period of tidal cycle 24 hours 50 minutes
• Semidiurnal
• Two high, two low tides per lunar day
• Period 12 hours 25 minutes
• Equal range

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• Mixed
• Two high, two low tides per lunar day
• Unequal range
• Most tides are mixed

19
Standing waves

• Forced standing wave caused by tides
• Free-standing waves caused by strong winds or
  seismic disturbances

Fig. 10-22
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• Node maximum horizontal flow
• Antinode maximum vertical flow

Fig. 10-23
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Bay of Fundy

• Largest tidal range (spring tide max 17 m)
• Shape of basin
• Oscillation period close to tidal period
• Shoals and narrows to north
• Basin oriented toward right (Coriolis moves
  water toward right)

Fig. 10-24
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Tidal bores

• Wave created by tide rushes upstream
• Large tidal range
• Low-lying coastal river
• Max 8 m high

Fig. 10A
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End of Chapter 10 Tides
Fig. 10-6
Fig. 10-7