Chapter 10-Waves Flashcards
Progressive waves
- Have a speed and move in a direction
- Surface waves (deep & shallow water waves), big waves (tsunamis, large swells, episodic waves), internal waves (at pycnocline; long periods, large heights, slower speed than surface waves)
- A wave of moving energy in which the wave form moves in one direction along the surface (or junction) of the transmission medium (or media). In transverse waves the displacement of the particles in the medium is perpendicular to the direction the wave is travelling in.
Stokes drift
A small net transport of water in the direction a wind wave is moving
Which way do water molecules in a wave move?
Water molecules in the crest move in the same direction as the wave, but the molecules in the trough move in the opposite direction
Forced wave
A progressive wave under the continuing influence of the forces that formed it. Ex: tides
Crest
Highest part of a progressive wave above average water level
Capillary and gravity waves are named for the __________.
dominant restoring force
The height of a wave depends upon __________.
fetch, wind duration, and wind speed
How far down does the orbital motion of water molecules in a wave reach?
The orbital motion of water molecules in a wave goes down to a depth equal to the wavelength divided by two.
Compared to surface waves, internal waves are _______.
slow, long wavelength, and of great height
The largest wind-generated waves tend to be associated with __________.
the westerlies
What limits the size of capillary waves?
Surface tension
A deep-water wave occurs when the water depth is equal to __________.
1/2 of wavelength
fetch refers to __________.
the distance over which wind blows without interruption
The ratio of wave height to wavelength is called the __________.
wave steepness
Stokes drift
The slight forward motion which occurs in the water as a wave passes by
What is wavelength?
The distance measured from trough to trough or crest to crest
The generating force of a gravity wave is ______.
density
Storm surges are associated with __________.
associated with the onshore arrival of a powerful cyclonic storm
Wave height is ___________.
The vertical distance between crest and trough
Diameter of the orbits of water particles in deep water and in shallow water
Deep water: equal to wave height. Shallow water:
Wave speed is equal to __________.
wave speed=wavelength divided by period
The speed of a shallow-water wave is proportional to __________.
wave depth
The speed of a deep-water wave is proportional to __________.
wavelength
A wave’s period is ______________.
The time between two successive waves
Describe the motion of water particles near the bottom in shallow water
becomes a back-and-forth motion
Why can wind waves travel over great distances in virtually straight lines?
Wind waves carry only energy, and energy has no mass, and is therefore not subject to Coriolis deflection.
Waves with the greatest propagation rate or velocity __________.
have the longest wavelengths
As the wind velocity increases during a storm, __________.
the wave height increases
Most waves in the open ocean have an average height of __________.
less than 3 meters
Constructive interference
When several wave crests or troughs coincide; results in larger waves
Destructive interference
When the crest of one wave coincides with the trough of another wave; results in smaller waves
What causes a wave train?
wave energy moving more slowly than individual waves.
Waves at the shore will start to break when
the water depth is about four-thirds the wave height
When waves approach the shore, if the bottom is a steep slope, __________.
the wave will plunge
Waves tend to be parallel to the shore when they break due to
The process of refraction
Standing waves may be caused by
wave reflection
As a wave begins to feel bottom near a shoreline,
its wave height increases and wavelength decreases
A wave will break when _________
water depth = wavelength/20
In the open sea, tsunamis reach an average wave height of about
1 meter
When a tsunami reaches shore, __________.
the wave height is increased by entry into shallow water
Radius of the earth
6,400 km
Tropsophere
Lowest layer containing most of Earth’s atmosphere (75-80%). Tropopause (boundary btwn trosophere and stratosphere) is usually at ~10km - the jet stream is just below this. The height of the top of the troposphere varies with latitude** (it is lowest over the poles and highest at the equator), **with season (it is lower in winter and higher in summer), and time of day. It can be as high as 20 km near the equator, and as low as 7 km over the poles in winter.
Almost all weather occurs within this layer [nearly all of the water vapor and dust particles in the atmosphere are in the troposphere. That is why mostclouds are found in this lowest layer, too]. It is warmed from below (sunlight warms the ground or ocean, which in turn radiates the heat into the air right above it); air is warmest at the bottom of the troposphere near ground level, and temperature decreases with altitude (higher up it gets colder). Air pressure and density also decrease with altitude.
The troposphere is heated from below. Sunlight warms the ground or ocean, which in turn radiates the heat into the air right above it. This warm air tends to rise. That keeps the air in the troposphere “stirred up”. The top of the troposphere is quite cold. The temperature there is around -55° C
Height of stratosophere
~10 km above sea level (varies with latitude, season, and whether it’s day or night; can be as high as 20km over the equator, and as low as 7 km over the poles in winter)
Explain variations in the height of the troposphere
Deep convection (thunderstorms) in the ITCZ (low pressure), or over mid-latitude continents in summer, continuously push the tropopause upwards and as such deepen the troposphere. {This is because thunderstorms mix the tropospheric air at a moist adiabatic lapse rate. In the upper troposphere, this lapse rate is essentially the same as the dry adiabatic rate of 10K/km.} A deepening by 1 km reduces the tropopause temperature by 10K. Therefore, in areas where (or at times when) the tropopause is exceptionally high, the tropopause temperature is also very low, sometimes below -80C. Such low temperatures are not found anywhere else in the Earth’s atmosphere, at any level, except in the winter stratosphere over Antarctica.
On the other hand, colder regions have a lower tropopause, obviously because convective overturning is limited there, due to the negative radiation balance at the surface. In fact, convection is very rare in polar regions; most of the tropospheric mixing at middle and high latitudes is forced by frontal systems in which uplift is forced rather than spontaneous (convective). This explains the paradox that tropopause temperatures are lowest where the surface temperatures are highest.
The tropopause height does not gradually drop from low to high latitudes. Rather, it drops rapidly in the area of the subtropical and polar front jets (areas of
Standing waves
- Also called seiches
- Do not progress (they are progressive waves reflected back on themselves) and appear as alternating troughs and crests at a fixed position called antinodes, oscillating about a fixed point called node.
- They occur in ocean basins, enclosed bays and seas, harbors and in estuaries.
Tsunamis
- Short heights, long wavelengths (>100 km), and long periods
- Progressive waves
- In shallow water their length shortens and their height increases dramatically
Refraction
Changes in depth refract waves: waves approaching shore are refracted (bent) as they move from deep to shallow water - change in wavelength and wave speed
Diffraction
when wave is passing through gaps: spread of wave energy sideways to the direction of wave travel.
Reflection
Continents reflect waves: Waves that encounter a solid vertical surface (such as a seawall) will abruptly change direction without much loss of energy. Though not as simple as a ball bouncing off a wall, the reflection of a wave obeys the same principles, where the angle of incidence is equal to the angle of reflection. When the angle is zero (as measured from a line perpendicular to the reflecting surface), reflection may generate standing waves.
Earth’s circumference
40,000 km
wavelength, other characteristics
Tides
Periodic, short-term changes in height of ocean’s surface
20,000 km (1/2 of Earth’s circumference [40,000km]): longest of all waves!
Huge, shallow-water, progressive wave
Forced waves
MTL = Mean Tide Level
MHW = Mean High Water
MLW = Mean Low Water
MHHW = Mean Higher High Water
MLLW = Mean Lower Low Water
Tidal Range
MTL - computed from measurements taken at a place over many years and averaging all water levels.
tidal range – difference between MHW and MLW (water level at high tide and water level at low tide)
Flood Tide
High Tide
Ebb Tide
Low Tide
Slack Tide
Flood tide: tide wave is propagating (onto shore) onshore – water level is rising
High Tide: water level reaches highest point ** Bulges **
Ebb Tide: tide is moving out to sea – water level is dropping
Low Tide: water level reaches lowest point ** Troughs **
Slack tide: period when tide wave is reversing–low current velocity
