Recap Waves are energy moving through a substance a. Sometimes this movement is visible (waves on ocean surface) Waves are formed by some “disturbing force” – and weakened by a “restoring force” The depth of the water changes the behavior of the wave Wind is a common disturbing force that generates waves transfer of wind energy into water small amounts of energy produce small waves known as ‘capillary waves’ – rippling of water larger energy produces “wind waves” – this happens when the wavelength is > .68” (the point at which gravity – and not capillary action – is the dominant restoring force)
For most waves, gravity is the dominant restoring force. Figure 9.4 Wave energy in the ocean as a function of the wave period. As the graph shows, most wave energy is typically concentrated in wind waves. However, large tsunami, rare events in the ocean, can transmit more energy than all wind waves for a brief time. Tides are waves—their energy is concentrated at periods of 12 and 24 hours. Fig. 9-4, p. 202
Figure 9.4 Wave energy in the ocean as a function of the wave period. As the graph shows, most wave energy is typically concentrated in wind waves. However, large tsunami, rare events in the ocean, can transmit more energy than all wind waves for a brief time. Tides are waves—their energy is concentrated at periods of 12 and 24 hours. Fig. 9-4, p. 202
Tides -- the rise and fall of ocean levels -- wavelength can be as much as half of earth’s circumference Why???
Tides -- the rise and fall of ocean levels -- wavelength can be as much as half of earth’s circumference Why??? -- Rotational forces -- Gravitational forces -- of what??
Tides -- the rise and fall of ocean levels -- wavelength can be as much as half of earth’s circumference Why??? -- Rotational forces -- Gravitational forces -- of what?? -- Moon -- Sun
Tides -- the rise and fall of ocean levels -- wavelength can be as much as half of earth’s circumference Why??? -- Rotational forces -- Gravitational forces -- of what?? -- Moon -- Sun ALSO important – -- Tidal changes are influenced by the shape of near shore bottom
Our understanding of tides is not new 1687 – Isaac Newton describes gravitational forces. -- uses gravitational forces to explain tides! 323 years ago!
Our understanding of tides is not new 1687 – Isaac Newton describes gravitational forces. -- uses gravitational forces to explain tides! 323 years ago! We can use Newton’s equations to calculate the tidal force of the sun and moon. T= g ( m1m2/r3) g = gravitational constant m1 = mass of body1 (earth) m2 = mass of body2 (sun or moon) r = distance between the two centers
Our understanding of tides is not new T= g ( m1m2/r3) g = gravitational constant m1 = mass of body1 (earth) m2 = mass of body2 (sun or moon) r = distance between the two centers Sun = 27 million times more mass than the moon BUT earth is 387 times farther from the sun than from the moon
Math is a funny thing T= g ( m1m2/r3) Sun = 27 million times more mass than the moon Sun = 387 times farther than moon
Math is a funny thing T= g ( m1m2/r3) Sun = 27 million times more mass than the moon Sun = 387 times farther than moon
Math is a funny thing T= g ( m1m2/r3) Sun = 27 million times more mass than the moon Sun = 387 times farther than moon
Math is a funny thing T= g ( m1m2/r3) Sun = 27 million times more mass than the moon Sun = 387 times farther than moon
Math is a funny thing T= g ( m1m2/r3) Sun = 27 million times more mass than the moon Sun = 387 times farther than moon
Math is a funny thing T= g ( m1m2/r3) Sun = 27 million times more mass than the moon Sun = 387 times farther than moon
Math is a funny thing T= g ( m1m2/r3) Sun = 27 million times more mass than the moon Sun = 387 times farther than moon
Math is a funny thing T= g ( m1m2/r3) Sun = 27 million times more mass than the moon Sun = 387 times farther than moon
Math is a funny thing T= g ( m1m2/r3) Sun = 27 million times more mass than the moon Sun = 387 times farther than moon
Math is a funny thing T= g ( m1m2/r3) Sun = 27 million times more mass than the moon Sun = 387 times farther than moon In other words The moon has TWO TIMES the tidal force of the sun!!
Lunar tidal acceleration = 1.1x10-7g Solar tidal acceleration = .52x10-7g
Lunar tidal acceleration = 1.1x10-7g Solar tidal acceleration = 0.52x10-7g Next largest effect of all other celestial bodies is that of Venus at 0.000113 x solar effect or 0.00005876-7g
What about the Sun???? Lunar tides Solar tides – considerably smaller
Spring tides – additive effects of sun and moon being in line. -- High tides are very high, low tides are very low. -- Happen every month – nothing to do with seasons Figure 10.11 Relative positions of the sun, moon, and Earth during spring and neap tides. (a) At the new and full moons, the solar and lunar tides reinforce each other, making spring tides, the highest high and lowest low tides. Fig. 10-11a, p. 233
Neap tides – sun and moon are at right angles -- sun diminishes moon’s tidal force -- high tides are not very high; low tides are not very low.
Other factors influence tides: Shape of coastline slope and depth of shoreline weather continents
Dynamical Theory of Tides Due to the varying shapes, sizes, and depths of the ocean basins, there are 3 different patterns of tides: Diurnal (daily), Semidiurnal (twice daily), and Mixed
Tidal current – water rushing into or out of an area -- Flood current – rising tides -- Ebb current -- sinking tides “Slack Water” – time where there is no tidal current movement -- the point where tidal directions are reversed
All of this coming and going of water has a major impact on organisms --- hours of submersion and exposure --- changes in temperature --- changes in salinity --- changes in dissolved oxygen