Bay of Fundy (Canada)
Tides
Measuring tides
General description
Physical mechanism
Characteristics in different locations
Tidal resonance and tidal bore
Measuring tides
Records of the position of sea surface with respect to a fixed level (a datum)
tidal pole float tidal gauge Measuring tides
Time series of sea surface height
Hilo tide observations and predictions (PacIOOS)
Measuring tides
Examples of tidal time series General description
Up and down motion of sea level
Back and forth currents
Periodic (~12 hours and 24 hours)
Amplitude and timing vary from one location to another
Propagating shallow-water wave of very long wavelength (~10,000km)
Physical mechanism
due to the gravitational attraction of Moon and Sun on Earth and its ocean
and the rotation of Moon around Earth and the Earth-Moon system around the Sun
Moon Sun
Earth
Physical mechanism
due to the gravitational attraction of Moon and Sun on Earth and its ocean
and the rotation of Moon around Earth and the Earth-Moon system around the Sun
Moon Sun “It's complicated!”
Earth
Theory of equilibrium tides
Simplified problem
Earth-Moon system only
No rotation of Earth around its own axis
Earth covered with an ocean (no continents)
No friction
Theory of equilibrium tides
Centrifugal Force (varies withr)
r
d
Gravitational Force varies with 1/d2)
Theory of equilibrium tides
Theory of equilibrium tides
Theory of equilibrium tides
Theory of equilibrium tides
Theory of equilibrium tides
Tidal Force
Theory of equilibrium tides
Tidal Force
Theory of equilibrium tides
Tidal Force
Two Lunar Bulges
With Earth's rotation
Semi-diurnal Tide
B
A C ~ 1 day
D
Two Lunar Bulges
A B C D A
Lunar day
Lunar day is about 24 hours and 50 min
Semi-diurnal tide is 12 hours and 25 min
With Earth's rotation
Semi-diurnal Tide
B
A C 1 lunar day
D
Two Lunar Bulges
A B C D A
With Earth's rotation
Semi-diurnal Tide
C D A
equator 1 lunar day
Two Lunar Bulges
A B C D A
With Earth's declination
Diurnal Tide
C A B
tor ua eq 1 lunar day
Two Lunar Bulges
A B C D A
With Earth's declination
Mixed Tide
C B
A tor ua eq 1 lunar day
Two Lunar Bulges
A B C D A
With Earth's declination
Semi-diurnal Tide
C B tor ua eq 1 lunar day A
Two Lunar Bulges
A B C D A
Three types of tides
Diurnal Tide
Semi-diurnal Tide
Mixed Tide
Spring and neap tides
Spring Tide
Neap Tide
Two Spring/Neap Tides every 29 ½ days Spring and neap tides
Additional variations
Greatest tidal range
Lowest tidal range
Additional variations Spring Tide + Perigee = Proxigean Tides
Greatest tidal range
Lowest tidal range
Real tides
Tides are shallow-water waves (period 12-24 hours, size of an ocean basin)
Propagates counterclockwise in N.H. and clockwise in S.H.
Amphidromic points (weak tides at these locations)
Real tides
Bay of Fundy: Case of tidal resonance
Off-shore tides excite a natural mode of variability of the continental shelf or the bay
Tacoma Narrows Bridge Collapse
Tidal bore
Incoming tide forms a wave that travels up a river against the river current
Watch the "Bono" in Indonesia: A case of river surfing (Kampar River)