Tides

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Tides

• November 18-19, 2009

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What are Tides?

• A tide is defined as a periodic rise and fall of
  the sea surface
• very-long period waves noticeable only at the
  shoreline
• originate in the open ocean
• High tide wave crest reaches the shoreline
• Low tide wave trough reaches the shoreline

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Tidal Range Tidal Currents

• Tidal range - the difference in water height
  between high and low tides
• varies from a few cm to up to 48 feet (14 m) at
  the Bay of Fundy in Canada
• Tidal current horizontal movement of water that
  accompanies the rising and falling tide
• incoming current is a flood current
• outgoing is an ebb current
• strongest during high or low tides, weakest in
  between the two
• Animation
• Blue planet video segment

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What Causes Tides?

• Result from the gravitational pull of the moon
  and sun on the Earth.
• Newtons law of universal gravitation
• More massive an object, greater its gravitational
  pull
• Varies inversely as the square of the distance
  between objects
• Tide generating force
• vary inversely as the cube of the distance from
  the tide generating object.
• Therefore the moon has a greater effect on the
  tides due to its proximity

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Gravity, Inertia, and the Two Bulges
Moon

• Two tidal bulges (high tides) form
• Bulge on the moon side
• caused by gravitational attraction of moon and
  Earth exerted on the fluid (oceans)
• largest bulge
• overcomes inertia of water
• Bulge on the far side of the Earth opposite the
  moon
• caused by inertia the tendency of moving
  objects to continue moving in a straight line
• inertia exceeds gravitational force here

Gravitational force
Earth
Inertia
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Changing Angles and Changing Tides

• Moon revolves around the Earth
• Its declination - angle relative to the equator -
  increases and decreases
• Varies the height and intensity of tides
• Monthly variation
• Animation

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Changing Angles and Changing Tides

• Because of Earths tilted axis, the suns
  relative position (declination) to the equator
  changes throughout the year
• Minimum (spring/fall equinoxes)
• Maximum (summer/winter solstices)

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Frequency of Tides The Lunar Day

• Lunar orbit 29.5 days
• Lunar tide
• Solar tide (1/2 as large as lunar one)
• When both in alignment spring tides occur. When
  moon not in alignment, neap tides.
• Animation

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Tidal Variation due to Variation in Moon and
Earth Orbits.
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Continents in the Way .. Again

• Land masses can create three different tide
  patterns
• Diurnal
• Semidiurnal
• Mixed semidiurnal

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Tidal Cycles of the World
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Other factors affecting tides

• Shoreline and coastline topography
• Shape of bays and estuaries
• Local wind and weather patterns

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Tide Resources

• McNish, Larry. "RASC Calgary Centre - A Complete
  Guide to." 17 Dec 2007. 29 Oct 2008
  lthttp//calgary.rasc.ca/radecl.htmgt.
• "Tides and Water Levels." NOAA Ocean Service
  Education. 25 Mar 2008. National Oceanic and
  Atmospheric Association, U.S. Department of
  Commerce. 29 Oct 2008 lthttp//www.oceanservice.noa
  a.gov/education/kits/tides/welcome.htmlgt.