Wind & Air
How is wind created?
Flow of air from high-pressure (increased air density) areas to areas of low pressure (decreased air density).
What is the net direction of water transport under the influence of wind?
90 degrees
What causes the differences in water mass density that power thermohaline circulation?
Differences in salinity and temperature.
What type of waves are wind-generated waves?
What is the difference between deep water and shallow water wind-generated waves
Progressive Waves = transfer of energy, with no net motion of mass, causing orbital motion
There is some slight movement of orbits forward called Stoke's drift
If the seafloor is below orbital motion, then it's a deep water wave, whereas if the seafloor is within orbital motion, it is a shallow water wave
How does refraction impact how waves come into contact with the shoreline
It will focus wave energy on specific parts of the coast and cause breaking waves release wave energy that will impact sediment distribution
How does air movement change with density and latitude?
Warm, less dense air rises at the equator.
Cold, more dense air sinks at the poles.
What is a gyre?
A large, circular system of rotating ocean currents formed by wind patterns and the Earth's rotation
What is the current system that circulates oxygen and nutrients throughout both the surface and deep waters?
Global Conveyer Belth Model
What are the two types of wave interference?
- Constructive Wave Interference: Crests aligning with crests and troughs with troughs, resulting in a new wave with a higher amplitude
- Destructive Wave Interference: Crests aligning with troughs, resulting in a wave with much lower amplitude or total cancellation of the wave.
What is longshore drift, and how does it affect a beach?
Occurs when waves strike a beach and release energy, moving the wave energy parallel to the shoreline.
This causes beach drift, where small amounts of sediment are moved parallel to the beach in the same direction of the current
How does air density change with water vapor content and temperature?
Air with water vapor is less dense than dry air
Warm air is less dense than cold air
Ex. Warm, moist air is less dense than cold, dry air
What three components interact to create the patterns of surface circulation seen?
1. Wind Drag
2. Pressure Gradients
3. Coriolis Effect
What are the two water masses created at offshore Antarctica that dominate the bottom and deep?
- Antarctic bottom water (AABW) is produced at the surface of the Weddell Sea during the southern winter. It is high-density and flows north into the North Atlantic
- Antarctic Deep Water (AADW) is produced at a less extreme latitude, and it also flows north until it collides with North Atlantic Deep Water and dives underneath it, pushing NADW
Describe each part of the wave: Wave crest, Wave trough, Wave height, Wavelength, and Wave period
- Wave crest: highest part of a wave
- Wave trough: lowest part of a wave
- Wave height: vertical distance separating the crest from the trough
- Wavelength: horizontal distance between the crest of one wave and the adjacent wave
- Wave period: the time it takes for two successive crests to pass a fixed point (used to classify waves)
What is the difference between swell and storm beach profiles?
Swell profile forms from fair weather with low flat swell, resulting in the accumulation of sediment and beach growth
- Concave profile with broad berm and steep beach face
Storm Profile forms from high-energy waves attacking the beach and transporting sediment offshore
- Shorter berm and flattened beach face
How does the Coriolis effect impact the direction of winds in the hemispheres?
Deflect the air to the right in the Northern Hemisphere due to counterclockwise spin
Deflect the air to the left in the Southern Hemisphere due to clockwise
Earth's true spin direction is west to east
Where and how do upwelling and downwelling occur?
Upwelling: divergence of water causes valley-like dips, so water moves up to fill that space.
- Where the wind blows parallel to the shore, north to south in the N. Hemisphere, offshore transport
- Between two gyres
Downwelling: convergence of water causes pressure to build, so water moves down and away to relieve it
- Where the wind blows parallel to the shore, south to north in the N. Hemisphere, onshore transport.
- In the center of a gyre
What is the dominant water mass in the Pacific Ocean, along with some of its characteristics?
The dominant water type is called Common Water (CoW), which is a blend of North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW) that is injected by the Antarctic Circumpolar Current (ACC)
What are the three changes when waves hit shallow water?
What wave property stays constant?
- Transformation of the wave’s properties: Slows down, Wavelength becomes smaller, Wave height increases
- Wave refraction: Bending of the wave crest in response to changes in wave speed
- Collapse as a shore breaker
- Only stable property is the wave period, as it remains the same in deep and shallow water
What are some processes that act as inputs and outputs of sand to beaches?
Inputs:
- River Supply
- Cliff Erosion
- Onshore Transport
Outputs:
- Creation of Dunes
- Offshore Transport
What are the three main wind cells and the direction of their movement?
Hadley Cell; air rises at the equator, moves poleward until it cools, sinking back around 30 degrees
Ferrel Cell; reverse of Hadley and polar cells, directly driven by the movement of the other two cells, sinks at 30 degrees and rises at 60 degrees
Polar Cell; same movement as the Hadley Cell, except from 60 degrees to polar latitudes
What is a geostrophic current, and how does it change a gyre's structure?
Water converges at the center of the gyre, creating a hill, and due to pressure gradients and the Coriolis effect, water flows across the slope rather than down.
Causes more water to pile up in the western part of gyres, creating stronger, deeper currents (Western Boundary Intensification)
What are some of the different water masses within the Atlantic?
- Antarctic Bottom Water (AABW) and Antarctic Deep Water (AADW) dominate the bottom and deep
- North Atlantic Deep Water (NADW) is believed to come from the subpolar gyres in the Greenland, Norwegian, and Labrador Seas
- Antarctic Intermediate Water (AAIW) formed in the subpolar regions by the cooling of rising NADW in the Antarctic convergence
- Antarctic Deep Water (AADW) collides with North Atlantic Deep Water (NADW) and dives underneath it, pushing NADW up
- Mediterranean Intermediate Water (MIW) is created when an increase in salinity of surface water results in it sinking when the density is too high and fills the basin until overflow at the Gibraltar Strait, and it spills into the North Atlantic.
What are the four factors that determine the characteristics of waves generated by wind?
- Wind velocity: Wind speed increase causes an increase in wavelength, period, and height
- Wind duration: Time for the wave development
- Fetch: The highly chaotic area of water where wind comes into contact with the sea, creating waves. Outside of the fetch area will result in dispersion with big waves outrunning smaller waves
- Original sea state: Affects the way the water and the wind interact.
- The waves will grow until a maximum size determined by fetch and wind speed
What is the goal of structures like groynes, jetties, seawalls, and breakers?
What are some issues with these mitigation strategies?
Reducing erosion by minimizing sediment movement from beach drift and slowing down the incoming wave action
Doesn't prevent downdrift erosion, multiple structures must be built to continue to minimize erosion, and cost to maintain them