Climate: Climatic Change - Evidence, Cycles and The Future
20100418_Herman_Ridderinkhof_Getijden
1. Royal Netherlands Institute for Sea Research
1
Tides and shallow water sea research at NIOZ
Royal Netherlands Institute for Sea Research
but first: crossing the Agulhas current
NIOZ is part of the Netherlands Organisation for Scientific Research (NWO)
Herman Ridderinkhof
6. Tides
Herman Ridderinkhof
NIOZ and Utrecht University
What are the causes of tides and what are their characteristics?
How do tides propagate in oceans (e.g. Atlantic), shelf seas (e.g.
North Sea), shallow tidal basins (e.g. Wadden Sea)?
7. Daily
inequality
delay: moon phases - tidal phenomena
Neap tide
Spring tide
Two highs and
lows per day
General pattern of the vertical tide at one station
8. Examples:
“Lunar” frequencies
- lunar day
- 2 x lunar day (dominant)
- overtones
- eccentricity lunar orbit
- tilt lunar orbit
- etc...
“Solar” frequencies
- similar to moon freq.
And all kinds of crossterms
A tidal signal can be decomposed in a number of
frequencies related to astronomical frequencies
9. Astronomical forces
Tides are caused by the gravitational force of
the moon and sun and the motion of the earth-
moon-sun system
The gravitational force causes a deformation of
the ocean surface (equilibrium tide)
Frequencies of planetary motions result in
different ‘astronomical frequencies’
10.
11. Tidal frequencies: lunar day
A lunar day is the time that elapses between
when the moon is directly overhead and the
next time the moon is directly overhead.
During one complete rotation of Earth (the 24-
hour solar day) the moon moves eastward 12.2
degrees, and Earth must rotate an additional 50
minutes to place the moon in the exact same
position overhead.
Thus, a lunar day is 24 hours 50 minutes long
(and a solar day 24 hours).
14. There are lots of other “astronomical frequencies” :
example: relative tilts of plane of the Moon’s orbit and equator plane.
These variations are a.o. recognizable in geology.
17. Tide driven by astronomical forces is present only in the Southern
Ocean.
Amplitude of tide due to astronomical force, the equilibrium tide,
is 0.27 m due to the moon and 0.12 m due to the sun
Tides at any location outside the Southern Ocean are caused by
propagation of the tidal wave from the Southern Ocean
18. How do tides propagate in oceans and shelf seas?
William Thomson
(Lord Kelvin) Sea level displacement for a
Kelvin wave
19. Kelvin wave in a
square tank:
The Coriolis force
lets the wave run
along the wall on the
right side (northern
hemisphere)
21. The Kelvin waves in the
Atlantic Ocean start in
the south
For the tidal wave
it takes about 2-2.5
days to move from
the Southern Ocean
to the North Sea (spring
tide is 2-2.5 after full
moon)
22. Kelvin waves in the
North Sea
split up in
three separate
Kelvin waves
The “Knots”
are called
Amphidromic
points. Here is no
vertical tide
23. Resonance occurs if reflected wave from landward end amplifies the
incoming wave (length basin = .5 * tidal wave length)
Tides in Confined Basins: no Kelvin wave but
possibility of amplification due to resonance
24. The largest tidal range in
the world occurs in Nova
Scotia's Bay of Fundy. Even
though the maximum spring
tidal range at the mouth of
the bay is only 2 meters,
amplification of tidal
energy causes a maximum
tidal range at the northern
end of Minas Basin of 17
meters.
25. Bay of Fundy, High Tide
Bay of Fundy, Low Tide
27. Near-resonance in Wadden
Sea combined with strong
bottom friction
Tides in Wadden Sea have
become stronger due to
closure with Afsluitdijk!
28. Tide is excited by astronomical forces. ‘Ideal tide’ is present only
in the Southern Ocean (no continents).
Frequencies of the tide are related to astronomical frequencies
Tides propagate through the world oceans as rotating (Kelvin)
waves
Amplitude of the tide at a certain location strongly depends on the
resonance characteristics of a sea basin
Tides: important issues
29. 29
Some NIOZ Wadden Sea studies based on
our speciality: observations at sea
‘Navicula’ ‘Stern’ (Tern) Flatboat ’t Horntje’
Ferry based observations and studies
Ecological studies based on (long term) field
observations
33. Bottom depth of
the Marsdiep inlet,
and the changes
over time showing
migrating
sandwaves
34. A
Cross section of the bottom profile along section A
Migrating sandwaves into the WaddenSea with a
height of 2-3 m and a length of 100 m (dark is
orinigal profile)
35. B
Cross section of the bottom profile along section B
Migrating sandwaves into the WaddenSea with a
height of 7-8 m and a length of 300 m (dark is
orinigal profile)
36. 1 8 6 0 1 8 8 0 1 9 0 0 1 9 2 0 1 9 4 0 1 9 6 0 1 9 8 0 2 0 0 0
Y e a r
8
9
1 0
1 1
1 2
1 3
Temperature(oC)
M a r s d ie p
A n n u a l m e a n t e m p e r a t u r e
s in c e 1 8 6 1
1 8 6 0 1 8 8 0 1 9 0 0 1 9 2 0 1 9 4 0 1 9 6 0 1 9 8 0 2 0 0 0
Y e a r
2 6
2 8
3 0
3 2
3 4
Salinity
M a r s d ie p
A n n u a l m e a n s a lin it y
s in c e 1 8 6 1
Temperature,
Salinity
since 1861
(van Aken)
Now from
NIOZ jetty
