TIDES Flashcards
how are waves classified
by their physical characteristics
what kind of force forms waves
disturbing force
whats a Restoring force
flattens water surface
whats the most useful measure of wave size
Wavelength
what is the disturbing and restoring force for tides
gravity
what are tides
forced shallow-water waves formed by spatial variations in gravity
what does ‘forced’ mean
they are never free of the forces that cause them e.g. continuous wind causes waves
whats the equilibrium theory and who proposed it
Pytheas
describes how tides are influenced by the gravitational pull of the Moon and Sun on Earth’s oceans
- describes tides on a planet uniformly covered by water
who formalised the idea of the equilibrium theory
Isaac Newton - 1687 book - gravitational model of tides
does The Moon or sun have a stronger influence on tides and why
moon
- despite the Sun’s larger size, the Moon is much closer to Earth
why doesn’t the moon revolve around the center of Earth
Earth is much bigger than the moon - so the common center (barycenter) of mass resides inside the planet
why do tides form
differences in gravitational forces across earths surface - results in 2 bulges of water – one on same side of the moon and one on the opposite side
3 forces that generate tides
- Inertial movement - As Earth and the Moon orbit their common barycenter, inertia causes water on the side opposite the Moon to form a second bulge
- Gravitational attraction - Moon’s gravity pulls on Earth’s oceans, creating a bulge of water on the side facing the Moon
- Tractive forces - arise from the combination of both
2 complications when it comes to tides
- tidal cycle = 24 hours 50 mins - Lunar day is longer than solar day
- moon varies position in the sky each month – why we can get higher high tides sometimes and lower high tides other times
whats a spring and neap tide
spring = sun and moon aligned
neap = sun and moon misaligned
what are Semi-diurnal and diurnal tides
Semi-diurnal = 2x high and low tides a day (most common)
Diurnal = 1x high tide and low tide a day
whats The Dynamic Theory and who proposed it
Laplace
improvement on Equilibrium Theory by considering real-world complexities in how tides behave.
what 3 things does the Dynamic Theory take into account
- The speed of the long-wavelength tide wave in relatively shallow water
- The presence of interfering continents
- The circular movement / back-and-forth rocking of water in ocean basins
whats a Tidal datum
the reference level to which tidal height is compared
whats the mean sea level
the height of the ocean’s surface average over a few year’s time
whats the tidal range
high-water to low-water height differences
what is Amphidromic Circulation
areas of little to no tidal movement
- don’t develop in confined spaces (like small bays or narrow channels) - no room for the tidal waves to circulate
what is a A tidal bore
a true tidal wave – tide come very fast in wave like motion
how has tidal friction and forces influenced the earth
- gradually slowing the Earth’s rotation
- locked the rotation of the moon to that of Earth - same side of the moon always facing Earth
can tides be predicted
yes - There are at least 140 tide-generating and tide-altering forces and factors
- Experience permits predication of tidal height to an accuracy of about 3 centimeters (1.2 inches) for years in advance
Factors which can alter predicted tide times
- Storm surge
- Atmospherically induced seiching of the basin
- Large scale resonances by a tsunami
- Strong steady wind on-shore or offshore
what are Meteorological tides
weather related alterations
what can be used to study tides
satellites - variations in magnetic field
how can Tidal waves provide electrical power
underwater turbines
