What causes tides?
the gravitational force of the moon and the sun on a diurnal/semidiurnal time scale
What are tides?
very long period waves that move through the ocean and are impacted by the gravitational pull of the Moon and the Sun
Diurnal tide pattern
one high and one low daily
Semi-diurnal tide pattern
two highs and two lows daily
Semidiurnal mixed
two tidal cycles per day but uneven highs and lows
Rising tide =
ebb
Falling tide =
flow
Why is a tidal day 24 hr, 50 min?
the moon revolves around Earth in the same direction that Earth is rotating on its axis, so it takes Earth an additional 50 minutes to “catch up” to the Moon
How does the Sun play a role in tides?
produces a “Sun” bulge although the gravitational effect is reduced due to distance from Earth
What is the net effect of the Sun compared to the Moon?
net effect of Sun is only 46% that of the Moon due to greater distance from Earth
Spring tides
Sun and Moon are aligned; greatest range
Neap tides
Sun and Moon are not aligned; smaller range
Equilibrium Tidal Theory
Assumes no continents and a uniform global ocean
Diurnal tides at high latitudes, semidiurnal at low latitudes, and mixed in between
Dynamic Tidal Theory
Continents disrupt the moon-following wave around the globe
Because the tidal wave is contained within individual basins, it can oscillate back and forth as a standing wave
also impacted by Coriolis
Progressive tide
the wave traverses the ocean like a shallow-water wave
Standing wave
a basin is such that the wavelength is twice the length of the basin
Rotary standing wave
Coriolis produces a clockwise spiral
