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Tides
 

Tides

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    Tides Tides Presentation Transcript

    • Tides
    • Tides
    • At earth’s center: centripetal acceleration = centrifugal acceleration (at common center of mass).
      The period of rotation about this common center of mass is 27.32 days (sidereal month).
      Everywhere else on the earth, there is an imbalance between the centripetal (inward) and centrifugal (outward) accelerations. The centrifugal acceleration is the same everywhere on the earth, but the gravitational force due to the moon varies over the surface of the earth.
    • This results in the tide-generating force, TGF, since on the side of the earth toward the moon the gravitational force exceeds the centrifugal force, and on the side of the earth away from the moon the centrifugal force exceeds the gravitational force. The �sideways� forces, or horizontal component, of the TGF is called the tractive force.
      Note: Centripetal Force and Centrifugal Force is the action-reaction force pair associated with circular motion (Newton’s Third Law).
    • The equilibrium tide is that which would result from the TGFs if the earth were completely covered by water and responded instantly to the changing forces (i.e. no inertia and no friction). As a result of the tractive forces, the equilibrium tide has two bulges, one on either side of the earth. Thus, you see 2 highs and 2 lows per lunar day (semidiurnal lunar tidal constituent). It has a period of 12.42 hours and is denoted by the symbol M2.
    • The lunar day (also known as a tidal day), 24.84 hrs, exceeds the solar day (24 h) since the moon is revolving around the earth with a period of 27.32 days.
    • Tides
      High tides occur every 12 hr 25 min 1 lunar day = 24 hr 50 min
      • Gravitational forces of sun and moon add at full and new moon to produce spring tides.
      • Gravitational forces of sun and moon compete at half moon to produce neap tides.
    • Moon declination
    • Moon declination effect
      A = Semidiurnal B = Mixed C = Diurnal
    • Tides
      [14.79 days]
    • Earth orbit around the sun
    • Tides
      There are three types of tides:
      Semidiurnal
      Mixed
      Diurnal
    • Tides: Moon declination effect
      A = Semidiurnal B = Mixed C = Diurnal
    • Monthly tides
    • Global distribution of tides
    • Local influences on tides
      Shape of the land
      Shape of the ocean floor (bathymetery)
      Depth of water
      Restrictions to flow (narrow inlets to bays, etc.)
      Local winds
    • How do we predict tides?
      XTide Tide Prediction Server
      http://www.mobilegeographics.com:81/
      http://tidesonline.nos.noaa.gov/monitor.html
      http://www.mobilegeographics.com:81/zones/:America/Puerto_Rico
    • Tidal “Wave”
    • Tidal Waves (Tsunamis)
    • http://www.ssc.erc.msstate.edu/Tides2D/tides_synopsis.html
    • Tidal “Wave”
    • Tidal “Wave”
      No rotation
      With rotation
      http://earthguide.ucsd.edu/earthguide/diagrams/waves/swf/wave_seiche.html
    • Tides San Juan, Puerto Rico
    • Largest tides
      Bay of Fundy, Nova Scotia, Canada
    • Largest tides
      Bay of Fundy, Nova Scotia, Canada
      Tidal range = 15 m (50 feet or a 3-story building)
      The largest tidal bore occurred in Hangzhou Bay, China, 1993. The bore was 9.14 m (30 ft) high.
    • Internal Waves
      Barotropic Wave
      Baroclinic Wave
      (internal tide or wave)
    • Internal Waves
      Red Sea True-color Terra MODIS, July 26, 2003.
    • Important terms:
      Barycenter
      Centripetal force
      Lunar and solar declination
      Tropics of Cancer and Capricorn
      Apogee
      Perigee
      Aphelion
      Perihelion
      Tidal day
      Semidiurnal, mixed, and diurnal tides
      Spring tides (syzygy)
      Neap tides (quadriture)
      Amphidromic point
    • Consequences of tidal fluctuations
      Navigation – depth and currents
      Intertidal – range and type of organisms
      Larval retention and dispersal
      Internal waves
      Migrations synced with
      tides
    • Tidal Resources
      http://tidesandcurrents.noaa.gov/
      http://oceanservice.noaa.gov/education/kits/tides/tides01_intro.html
      http://tidesonline.nos.noaa.gov/
      http://www.mobilegeographics.com:81/zones/:America/Puerto_Rico
    • Tides
      High tides occur every 12 hr 25 min 1 lunar day = 24 hr 50 min
      • Gravitational forces of sun and moon add at full and new moon to produce spring tides.
      • Gravitational forces of sun and moon compete at half moon to produce neap tides.
    • Tides
      [14.79 days]