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 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
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” 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