Waves & Tides Flashcards
waves form by ____ with air
friction
(energy from wind is transferred to waves)
What are the 4 principles of waves?
- only energy moves (there’s very little net movement of water horizontally or vertically)
- water particles move in circular orbits
- orbit diameter decreases with distance from the seafloor
- waves reflect from objects with no energy loss
the size of a wave’s circular orbit depends on ___ ___ and they become ___ against shores
wind speed
compressed
t/f
due to waves, the whole water column moves horizontally
false!
it moves in circular orbits
What is the crest of a wave? A trough?
crest= the highest point of a wave
trough= the lowest point of the wave surface
wave length (L) measures from ___ to ___ and it varies depending on amount of ____
crest to crest
energy
What is the height/amplitude (H) of a wave? What’s the period (t, sec) of a wave?
H= measure from trough to crest
t= time of passage of successive crests
What’s the depth of a wave?
How is the velocity of a wave measured?
D= half the length of a wave (L/2)
V= L/t for waves in deep water
Water motion is negligible when:
a) D < L/2
b) D > L/2
c) D = L/2
b) D > L/2
In deep water: waves action ____ the deeper you go
In shallow water: wave action doesn’t ____, the energy ___ off the bottom (orbits become ____)
diminishes
diminish
reflects
compressed
In shallow water, when does a wave become unstable and breaks?
When the ratio of height to length (H/L) is greater than 1/7
ie when the wave gets too high it breaks
when the water depth is less than half the length (D < L/2), the waves become ___ and particles are ____
elliptical
displaced
wind generates friction over the water, which first causes ____ then ____ then ____
ripples –> swells –> waves
final wave height is determined by 3 things:
1
2
3
- average velocity of the wind
- length of time the wind blows
- fetch: the distance over which the wind blows (high velocity= high fetch)
What are the 2 types of wind waves? How do they differ?
- local seas: have short periods (less than 8 secs) and are irregular
- wind driven - swell: long period (10-15sec) and are regular
- driven by distant weather conditions (energy transferred into the water and travels very far)
why don’t marginal seas experience swells?
swells are driven by distant weather conditions, so marginal seas don’t get them because they’re protected
What are 3 types of waves that are not wind waves?
rogue waves
tsunamis
internal waves
rogue waves=
summation of several wave trains (come from interaction of storms with currents)
unusually huge waves that come without warning
*not a wind wave
tsunamis=
caused by undersea earthquakes that can move up to 800km/h
they have long wavelengths (huge orbits) and lose very little energy
*not a wind wave
Internal waves are driven by ___, not ___
where do they occur?
density
wind
they occur where low density water lies over higher density water
In shallow waters, internal waves are influenced by ____. How?
tides
in an esturary where fresh water is coming out and the saltier water coming in with the tide = there’s a wedge
What are the 3 types of tides? Explain each
- diurnal: once a day (1 high per day & 1 low per day)
- semi-diurnal: twice a day
- mixed semi-diurnal: different highs and lows during the day (twice)
what causes the tides?
the gravitational pull of the sun and the moon
What does the type/ number of tides depend on?
location!
eg
- geography
- ocean vs marginal sea
- ice cover
The gravitational pull of the moon is ___ times stronger than the sun. Why?
6x!
because it’s closer
The moon’s rotation around the earth gives a monthly cycle of ___ and ___ tides. What are each?
spring and neap
Spring tides= greatest vertical tidal range (highest high and lowest low)
Neap tides= smallest vertical tidal range
Earth’s rotation gives a(n) ___ cycle of tides
Earth’s orbit around the sun gives a(n) ____ cycle of tides
daily
annual
Spring tides are highest with a ___ moon, and spring tides occur when the moon ___ (is/ isn’t) in line with the sun
new
spring tide= moon IS in line with the sun (& earth)
Neap tides occur when the moon __ (is/ isn’t) in line with the sun & earth
is not
How often do daily tide cycles occur and what causes them?
one cycle a day (12h 25min & 24hr 50min)
gravitational pull of the moon and the rotation of earth about the axis (1x per day)
- motion of the moon in the same direction as the earth’s rotation
Biweekly tide cycles (every 14 days) are caused by:
the rotation of the moon around the earth (~28 days)
- caused by combo of earth/ moon/ sun and their alignments
Half-yearly tidal cycles (every 6 months) are caused by:
rotation of the earth around the sun (~365 days)
- Earth, moon, sun interactions (orbits) and the tilt of the earth (diff distances from the sun)
Tide cycles in different locations are a function of ____, and basin ___/___
latitude
basin shape and size
What is a tidal bore and what causes it?
Tidal bore= tide moving up a channel against the retreating water
caused by the narrowing of channels
What is a Seiche and what causes it?
Seiche= a standing wave caused by the wave reflecting off shorelines (b/c of the channel narrowing)
How can weather (specifically atmospheric pressure) affect tides?
low pressure can cause storm surges or storm tides
eg. hurricane irma
