STU1033 Aquatic Science & Daily Life LU3: Waves and Tides PDF

STU1033 Aquatic Science & Daily Life LU3: Waves and Tides At the end of the unit, you should be able to: 1. Differentiate the tides and waves. 2. Understand natural phenomenon related to tides and waves. Acknowledgement: Notes are adapted from OpenCourseWar...

STU1033 Aquatic Science & Daily Life LU3: Waves and Tides At the end of the unit, you should be able to: 1. Differentiate the tides and waves. 2. Understand natural phenomenon related to tides and waves. Acknowledgement: Notes are adapted from OpenCourseWare@UNIMAS  Tides: Tides are the rise and fall (up and down) of sea levels caused by: the combined effects of gravitational forces exerted by the Moon, Sun, and Earth. the earth rotating on its axis underneath the water bulges.  Tidal Bulges: Earth © FARAH AKMAL IDRUS Moon Tidal bulge due to inertia Tidal bulge due to (rotational) force gravity force Tidal Bulges: The Moon’s Effect: also known as lunar bulges. tidal period: time between high tides (12 h 25 min). lunar day (24 h 50 min 28 sec) is longer than solar day (24 h) because Moon also rotates in its orbit & Earth have to “catch up”. evidence: each day alternating tides are normally 50 min later & Moon rises 50 min later.  Tidal Bulges: The Sun’s Effect: also known as solar bulges. its tide-generating forces is weaker (46% of the Moon) due to the distance (390 the distance between Moon & Earth). © FARAH AKMAL IDRUS Full Moon New Moon Lunar bulge Solar bulge * Illustration is not to the right scale. Which position of lunar bulges water show the development of: a. The spring tide? b. The neap tide? The Monthly Tidal Cycle: 29½ days, time for the Moon to complete an orbit around the Earth new moon: Moon is between Earth & Sun ¼ & ¾ moon: half-lit moon full moon: Earth is between Moon & Sun new & full moon = spring tide (large tidal range) due to combination of tide-generating forces of Moon & Sun.  The Monthly Tidal Cycle: ¼ & ¾ moon = neap tide (small tidal range) due to tide-generating forces of Sun is working at 90° to that of the Moon. time between 2 spring tides is ½ lunar cycle (about ~ 2 weeks). time between a spring & a neap tides is ¼ lunar cycle (about ~ 1 week).  1x Tidal Patterns: 2x Diurnal Semidiurnal single high & low tide per lunar day. 2 high & 2 low tides heights of successive per lunar day. high & low tides heights of successive about the same. high & low tides common in shallow approx. the same. inland seas (Gulf of common along Mexico & along the Atlantic Coast of US. coast of Southeast tidal period = 12 h 25 Asia). min. tidal period = 24 h 50 min.  mix Tidal Patterns: Mixed both characteristics of diurnal & semidiurnal. most common in the world. successive high tides & or low tides have significant different heights. tidal period = semidiurnal & diurnal.  A few interesting tidal phenomena: Extreme tidal range (~15 m), for example at the Bay of Fundy - the reflection & constructive interference of tidal wave in narrow basins connected to the Atlantic Ocean. At high At low tides tides Tidal bores is produced by an incoming high tide which go against the river flow in low-lying rivers.  Tidal Bores: Top 10 List: Qiantang Dragon, Haining Province, China (the largest bore in the world). Araguari Pororoca, Amapa State, Brazil Gironde Mascaret, Aquitaine, France Hugli Tidal Bore, West Bengal, India Lupar Benak, Sarawak, Malaysia Petitcodiac Tidal Bore, New Brunswick, Canada Schubenacadie Tidal Bore, Nova Scotia Seine Mascaret, Haute Normandie, France Severn Bore, Gloucestershire, England Turnagain Arm Tidal Bore, Alaska, USA  Exercise: Why do we need to know about the tides?  Waves: Lateral movement of the surface water. Influence by the wind (air-water interface) or by the fluids by different densities (water- water interface).  What causes Waves? (air – water interface): wind = surface waves (water – water interface): 1. different water densities (pycnocline) = internal waves (>100 m in heights but not energetic) 2. gravitational pull of moon & sun = tides 3. coastal landslide, calving icebergs = splash waves (530 m, Alaska) 4. sea floor movement = seismic sea waves/tsunami (85 m, Japan, very energetic) 5. ship & nuclear power testing = human-induced waves  Physical changes in waves: as waves approach shallow water, they undergo physical changes speed & wavelength reduce, but height increases release their energy at surf zone (zone of breaking waves)  Tsunami: Japanese word (harbor wave) or seismic sea waves. caused by sudden changes in the topography of the sea floor (e.g. vertical fault movement, volcanic eruptions). e.g. Wave Length > 200 km, undetectable Wave Height (0.5 m) in open ocean, Wave Speed > 700 km/h ~ jet plane. produces a series of rapid withdrawals & surges (one set = 1 to 7 surges, > 40 m, 4 m/sec). Tsunami: mostly occur in the Pacific Ocean (Pacific “Ring of Fire”). Pacific Tsunami Warning Center: since 1948 predict tsunami using real-time seismic waves beneath ocean surface. seismic wave travel 15x faster than tsunami. earthquake more than 6.5 magnitude are tsunamigenic. Rip Current: Mechanism  Rip Current: What to do? If caught in rip current: Best thing to do: Don’t fight the current. Know how to swim. Swim out of the current Never swim alone. (parallel to the shore), then If in doubt, don’t go out to to shore. beach. If you can’t escape, float or tread water. If you need help, call or wave for assistance. Another safety video...(in your own time) - The End of Unit 3 -