February 27th and March 1st lecture Flashcards
What are tides?
long period waves
What are high tides associated with in a wavelength?
The crest
What are low tides associated with in a wavelength?
The trouh
can currents also be assosated with tidal processes?
Yes
What are incoming currents associated with?
Rising tides, they are called flood currents
What are outgoing currents associated with?
Decreasing tides, these are called ebb currents
How fast can tidal currents be in coastal waters?
up to 5m/s
What cases bottom sediments to be suspended?
Tidal currents
Why are tides important?
- Slowly changes earth rotation and length of a day
- causes the moon to slowly move away from the earth
- Keeps the same face of the moon always facing the earth.
How do the tides affect the earth and moon ( angular momentum )
Oceanic tides lag behind the tide-generating potential and thus produces forces that transfer angular momentum between the Earth and the Moon
True/false: can tides influence the orbits of satellites?
True:
Tides influence the orbits of satellites
What is the main causes of tides?
Gravity is the main force that generates tides.
What does Newtons Theory of Gravitational Attraction state about the gravitational attraction between two bodies?
- it is directly proportionally to their masses
- it is inversely proportional to the square of the distance between the two bodies.
What are tidal forces based off of?
The gravitational attractive force, but varies inversely as the cube of the distance between objects.
What is the equation for the tide generating force?
TGF ( inversely proportional to ) Mass/Distance^3
Now, if the sun if 27 million times more
massive than the Moon and is 390 times
farther away from the Earth, the ratio of its
tide generating force to that of the moon is
27 million / (390)63 = 0.46
How are tidal bulges created? ( three things )
- Gravitation attraction strongest on side facing the moon
- causes water on near side to be pulled towards the moon
- Inertial forces try to keep the water in place, but the gravitational force is larger and a budge appears facing the moon?
Why is there two tidal bulges?
- On the opposite side of the earth, Gravitational attraction is weaker.
- Hence inertial forces ( centrigufal )exceed the gravitational force
- Thus the water moves away from the moon, forming another tidal bulge
How many tidal bulges do we have?
Two
Do the tidal bulges move?
no they do not, they stay in line with the moon, as the earth moves
Does anything other than the moon affect tidal bulges?
Interaction with the
sun modifies the tidal
bulges
What is lunar declination?
As the moon revolves around the Earth, its angle increases and decreases in relation to the equator
how does lunar declination affect the tides?
The two tidal bulges track the changes in lunar declination, also increasing or decreasing their angles to the equator
What is a Solar day?
Time for a specific point on the earth to rotate from
an exact point under the sun back to that same exact point (24
hours)
What is a lunar day?
Time it takes for a specific site on the Earth to
rotate from an exact point under the moon to the same point
under the moon
– 24 hours and 50 minutes long
How many bulges does earth pass through each lunar day?
Two, meaning that there is 2 high tides and 2 low tides
Where does the a lunar day take 50min longer than a solar day?
Extra length is because moon revolves around the earth in the
same direction as the earth rotates around its axis, needing the
extra 50 minutes to “catch up”
Does the sun exert a tidal force?
Although not as big as the moons, it still exerts a significant tidal force?
What happens to the tidal bulges when the sun and moon are aliened?
the solar bulge has an
additive effect on the lunar bulge, creating extra high and very low
tides
What is the tide called when the sun and the moon are aliened.
Spring tides
What happens to the tidal bulge when the sun and the moon are at right angels to one another?
their bulges partially cancel out, producing more moderate tides
What is the tide called when the sun and the moon are right angels to one another?
Neap tides
How often do spring and neap tides happen?
Alternatively around every 7 days
The Earth has an elliptical
orbit, being closest to the sun in N.H. winter. what happens to the tide at this point?
Tidal ranges are thus largest in January (smallest distance)
The moons orbit is also not perfect, with an 87 variance in distance, what happens to the tides as the moon gets closer or farther?
producing changes in tidal amplitude (including strong spring tides and weaker
neap tides)
Due to the bulges being offset because of the variations in the moon declination, how can it affect tides?
– An island can pass through the bulge on one side of the Earth but
miss it on the other
– Thus not all locations get two high tides and two low tides of the
same amplitude each lunar day
What is a Diurnal tide?
: Have one high tide and one low
tide each tidal day.
What is a semi-diurnal tide?
Have 2 high and 2 low tides
each tidal day, with the highs and lows having the same height
What are mixed tides?
Have 2 high tides and 2 low tides
each day
– But the heights of the 2 high tides and/or the 2 low tides
are different
What else affects tides?
The shape of the shoreline can strong affect the tides
What can wide continental margins do to tides?
They can lead to increased tide amplitudes
What kind of tides do mid-oceanic islands experience?
small tides
What kind o tides do funnel shaped days experience?
Funnel-shaped bays in particular can dramatically alter tidal magnitude
Can wind and weather affect tides?
Yes, local wind and weather can affect tides on a small scale.
