NR 150 1st Edition Lecture 11Outline of Last Lecture I. Circulation vs. WavesII. Waves: ConceptOutline of Current Lecture III. Comparison: Deep water vs. Shallow water wavesIV. TsunamiV. Comparison: Tsunamis vs. TidesVI. Tides and forces that generate themVII. Tidal friction gradually slows Earth’s rotationCurrent LectureI. Comparison: Deep water vs. Shallow water wavesa. Deep water wavei. Depth is more than L/2 (L=wavelength)ii. Speed1. C=L/Ta. C= speed (celerity; m/s)b. L=wavelength (m)c. T=time (period; s)iii. The longer the wavelength, the faster the wave will travelb. Shallow water wavei. Depth is less than L/2ii. Speed1. C=√gda. C= speed (celerity; m/s)b. g= acceleration due to gravity (9.8 m/s2)c. d= depth of water (m)iii. the depth of the ocean limits how fast the wave can travelII. Tsunamia. Long-wavelength, shallow-water progressive waves caused by the rapid displacement of ocean wateri. The speed shallow-water waves can travel depends on the water depthii. In the deep ocean, tsunami waves can travel the speed of commercial jetlinersThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.iii. Arrival time of tsunami waves at distant shores can be predictediv. Tsunami warning networks can save livesb. Tsunami caused by the sudden movement of faults are correctly called seismic sea wavesi. Can also be caused by landslides, icebergs falling from glaciers, volcanic eruptions, asteroid impacts, and other direct displacements of ocean waterc. Affected by ocean bottom contours and are often refracted around bottom features in unexpected waysd. Sumatra tsunami in 2004i. Fault along a subduction zoneii. 33 foot water displacemente. Japan tsunami in 2011i. Fault along a subduction zoneii. 20 foot water displacementIII. Comparison: Tsunamis vs. Tidesa. Tsunamisi. Shallow water wavesii. Free wavesiii. Triggered by seismic events and other events that displace wateriv. Restoring force: gravityb. Tidesi. Shallow water wavesii. Forced wavesiii. Result from gravitational forces from moon and suniv. Restoring force: gravityIV. Tides and forces that generate thema. Tides are caused by the gravitational force of the moon and sun and the motion of Earthb. The wavelength of tides can be half the circumference of earthi. Tides are the longest of all wavesc. Tides are forced waves because they are never free of the forces that cause themd. The Earth-Moon systemi. The moon doesn’t rotate around the center of Earthii. The Earth and mon together rotate around a common center of mass about 1650 km beneath Earth’s surfacee. Meteorological tides: weather related alterations to tidesi. Areas of low atmospheric pressure cause domes of waterf. Two tidal bulges are generatedi. The moon’s gravity attracts the ocean towards itii. The motion of the center of mass of the Earth-moon system throws up a bulge on the side of Earth opposite of the mooniii. The combination of the two effects creates two tidal bulges1. Water bulge resulting from inertia (centrifugal forces)2. Water bulge resulting from gravitational attraction to the moong. Sun and Moon influence the tides together (astronomical tides)i. At the new and full mons, the solar and lunar tides reinforce each other, making spring tides, the highest high and lowest low tidesii. At the first- and third-quarter moons, the sun, Earth, and moon form a right angle, creating neap tides, the lowest high and highest low tidesiii. Astronomical tides: the tides caused by inertia and gravitational force of the sun and mooniv. Amphidromic point: a node near the center of the ocean basin; a no-tide point in the ocean, around which the tidal crest rotates through one tidal cycle1. Development of amphidromic circulationa. A tide wave crest enters an ocean basin in the Northern Hemisphereb. The wave trends to the right because of the Coriolis effect, causing a high tide on the basin’s eastern shorec. Unable to continue turning to the right because of the interference of the shore, the crest moves northward, following the shoreline and causing a high tide on the basin’s northern shored. The wave continues its progress around the basin in a counterclockwise direction, forming a high tide on the western shore and completing the circuit. The point around which the crest moves is the amphidromic pointh. Three common types of tidesi. Semidiurnal tides: occur twice in a lunar day; two high tides and two low tides of nearly equal levelii. Diurnal tides: occur once each lunar day; one high tide and one low tideiii. Mixed tides: describe a tidal pattern of significantly different heights through the cyclei. Tidal patterns vary with ocean basin and sizei. Tidal range is the height difference between high and low tidesii. A tidal bore forms in some inlets (when inlets are exposed to great tidal fluctuation), results in a true tidal waveiii. Tidal currents in bays and harbors1. Flood current- tide crest2. Ebb current- tide trough3. Slack water- midway between high and low tideiv. True amphidromic systems can’t develop in narrow basins because their isn’t any room for rotationV. Tidal friction gradually slows Earth’s rotationa. 350 million years ago- 400-410 days/yr, 22 hrb. 280 million years ago- 390 days/yr, 22.5