19_tides_arbic - GeoSci 222 February 25, 2011 Supplementary...

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GeoSci 222 February 25, 2011 Supplementary Lecture Tides Brian Arbic
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Extra lecture on tides Professor Lund asked me to give you an extra lecture on tides, one of my research specialties. For the most part we will discuss material which is beyond what is in your book.
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KEY QUESTIONS FOR THIS LECTURE What tools are used in modern tidal research? What do tides really look like in the ocean? Are there tides in the solid earth? Are there tides elsewhere in the solar system? What is a tidal bore? What are some of the unanswered questions about tides?
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Equilibrium versus actual tides Actual tides in the ocean are much more complicated than the simple bulges (equilibrium tide) described earlier in the week. Instead, as Professor Lund noted: The actual tide is a dynamical response of the oceans to the equilibrium forcing, and does not look like the equilibrium tide Tides move as shallow-water gravity waves, but the ocean is not deep enough to make the waves fast enough for them to keep up with the positions of the Moon and Sun. Continents get in the way. Coriolis effect (due to Earth’s rotation) is important. Shape of seafloor is important, since wave speed depends on depth. Frictional effects control the strength of the tides. Solid earth also has a tide; this affects ocean tides because it changes the seafloor which tides are measured against, as well as the gravitational potential.
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Key question—what tools are used in modern tidal research? Tidal research has been revolutionized by the launch of satellite altimeters, which can accurately measure tidal sea surface elevations from orbit. (Digression: the NASA scientist who heads the altimeter project, Dr. Lee-Lueng Fu, will visit and give seminars here at UM April 6-8) Another important advance in tidal research (and
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19_tides_arbic - GeoSci 222 February 25, 2011 Supplementary...

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