NR 150 1st Edition Lecture 11 Outline of Last Lecture I Circulation vs Waves II Waves Concept Outline of Current Lecture III Comparison Deep water vs Shallow water waves IV Tsunami V Comparison Tsunamis vs Tides VI Tides and forces that generate them VII Tidal friction gradually slows Earth s rotation Current Lecture I II Comparison Deep water vs Shallow water waves a Deep water wave i Depth is more than L 2 L wavelength ii Speed 1 C L T a C speed celerity m s b L wavelength m c T time period s iii The longer the wavelength the faster the wave will travel b Shallow water wave i Depth is less than L 2 ii Speed 1 C gd a 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 travel Tsunami a Long wavelength shallow water progressive waves caused by the rapid displacement of ocean water i The speed shallow water waves can travel depends on the water depth ii In the deep ocean tsunami waves can travel the speed of commercial jetliners These 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 IV iii Arrival time of tsunami waves at distant shores can be predicted iv Tsunami warning networks can save lives b Tsunami caused by the sudden movement of faults are correctly called seismic sea waves i Can also be caused by landslides icebergs falling from glaciers volcanic eruptions asteroid impacts and other direct displacements of ocean water c Affected by ocean bottom contours and are often refracted around bottom features in unexpected ways d Sumatra tsunami in 2004 i Fault along a subduction zone ii 33 foot water displacement e Japan tsunami in 2011 i Fault along a subduction zone ii 20 foot water displacement Comparison Tsunamis vs Tides a Tsunamis i Shallow water waves ii Free waves iii Triggered by seismic events and other events that displace water iv Restoring force gravity b Tides i Shallow water waves ii Forced waves iii Result from gravitational forces from moon and sun iv Restoring force gravity Tides and forces that generate them a Tides are caused by the gravitational force of the moon and sun and the motion of Earth b The wavelength of tides can be half the circumference of earth i Tides are the longest of all waves c Tides are forced waves because they are never free of the forces that cause them d The Earth Moon system i The moon doesn t rotate around the center of Earth ii The Earth and mon together rotate around a common center of mass about 1650 km beneath Earth s surface e Meteorological tides weather related alterations to tides i Areas of low atmospheric pressure cause domes of water f Two tidal bulges are generated i The moon s gravity attracts the ocean towards it ii The motion of the center of mass of the Earth moon system throws up a bulge on the side of Earth opposite of the moon iii The combination of the two effects creates two tidal bulges 1 Water bulge resulting from inertia centrifugal forces 2 Water bulge resulting from gravitational attraction to the moon g 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 tides ii 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 tides iii Astronomical tides the tides caused by inertia and gravitational force of the sun and moon iv 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 cycle 1 Development of amphidromic circulation a A tide wave crest enters an ocean basin in the Northern Hemisphere b The wave trends to the right because of the Coriolis effect causing a high tide on the basin s eastern shore c 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 shore d 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 point h Three common types of tides i Semidiurnal tides occur twice in a lunar day two high tides and two low tides of nearly equal level ii Diurnal tides occur once each lunar day one high tide and one low tide iii Mixed tides describe a tidal pattern of significantly different heights through the cycle i Tidal patterns vary with ocean basin and size i Tidal range is the height difference between high and low tides ii A tidal bore forms in some inlets when inlets are exposed to great tidal fluctuation results in a true tidal wave iii Tidal currents in bays and harbors 1 Flood current tide crest 2 Ebb current tide trough 3 Slack water midway between high and low tide iv True amphidromic systems can t develop in narrow basins because their isn t any room for rotation V Tidal friction gradually slows Earth s rotation a 350 million years ago 400 410 days yr 22 hr b 280 million years ago 390 days yr 22 5 hr