chapter 10: tides fig. 10-7 fig. 10-6. tide-producing forces gravity and motions among earth, moon,...
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Chapter 10: Tides
Fig. 10-7
Fig. 10-6
Tide-producing forces
Gravity and motions among Earth, Moon, and Sun
Fig. 10-2
Centripetal force “tethers” Moon to Earth Directed away
from barycenter
Fig. 10-4 a,b
Resultant tidal forces
Gravitational force, Earth and Moon
Centripetal force, Earth and Moon
Resultant force moves ocean water horizontallyFig. 10-7
Fig. 10-6
Tidal bulges Two equal and
opposite tidal bulges
Earth rotates beneath tidal bulges
Two high tides Two low tides Per day Fig. 10-8
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
Lunar day Moon revolves around Earth Earth has to “catch up” with Moon
to reach same position
Fig. 10-9
Time between successive high tides shifts day after day
Moon rises later each successive night
Solar tidal bulges
Tide-producing force of Sun less than half of Moon’s
Sun much farther away
Month tidal cycle Spring tides
New Moon, Full Moon
Earth, Moon, Sun syzygy
Higher than usual high tides Fig. 10-12
Neap tide First Quarter,
Last Quarter Earth, Moon,
Sun quadrature
Lower than usual high tide
Fig. 10-12
Declination of Sun and Moon
Orientation of Sun, Moon to Earth’s equator Sun 23.5o N and S, yearly cycle Moon 28.5o N and S, monthly
cycle Unequal tides
Successive tides different tidal range
Unequal tidal range
Fig. 10-15
Elliptical orbits Perigee
Lunar tidal force greater
Higher high tides
Apogee Lunar tidal force
lesser Lower high tides Fig. 10-16
Dynamic theory of tides
Tide shallow-water wave Speed varies with depth Lags behind Earth’s rotation
Rotary flow in open ocean basins Amphidromic point Cotidal lines
Rotary flow
Crest (high tide) rotates Counterclockwise in
Northern Hemisphere Clockwise in Southern
Hemisphere
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
Mixed Two high, two low tides per lunar day
Unequal range Most tides are mixed
Standing waves
Forced standing wave caused by tides
Free-standing waves caused by strong winds or seismic disturbances Fig. 10-22
Node maximum horizontal flow
Antinode maximum vertical flow
Fig. 10-23
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
Tidal bores
Wave created by tide rushes upstream
Large tidal range
Low-lying coastal river
Max 8 m highFig. 10A
End of Chapter 10: Tides
Fig. 10-7
Fig. 10-6