Surface currents - 6 Flashcards
Why does equatorial low pressure occur?
- intense heating
- high moisture content
- rising air here
Why does polar high pressure occur?
- cold, dry dense air sinking
- creates an area of divergence at the surface
What is Coriolis deflection?
The apparent deflection of objects moving across Earth’s surface
Where is the maximum rotational velocity of the earth?
At the equator
Where is the minimum rotational velocity of the earth?
At the poles
Why does a zonal wind system develop?
Due to unequal surface heating and Coriolis deflection
What are the doldrums?
A belt around the earth near the equator with low pressure due to rising air here
What are the horse latitudes?
Latitudes around 30º where cooler and dense air sinks
What latitude does the Ferrel extend to?
30º to 50º
What latitude does the polar cell extend to?
50º to 900
What produces wind driven ocean currents?
Frictional interaction between wind and water
How does the speed of the wind and the induced current differ?
The induced ocean current is about 3-4% of the velocity of the wind
What are zonal wind flows?
Winds that move nearly parallel to latitude as a result of the Coriolis deflection
What generates westward ocean currents?
Easterly trade winds
What generates eastward ocean currents?
Westerly trade winds
How are gyres created?
Westward and eastward driven ocean currents are deflected by continents, creating a circular flow around basins
What height difference is observed over the ocean surface, from mounds to depressions?
1 metre
How are ocean mounds formed?
Due to convergences where water sinks (downwelling)
How are ocean depressions formed?
Due to divergences where water rises (upwelling)
What is the Ekman Sprial?
The resultant pattern caused by changes in current direction and speed with depth
What is Ekman transport?
The net transport of water by wind-induced motion. Net transport is perpendicular and to right in the northern hemisphere and perpendicular and the left in the southern hemisphere
What effect does Ekman transport have at the coast?
Can induced upwelling or downwelling
When is upwelling induced?
- When nearshore surface water is driven seaward
- When gyres diverge (Ekman divergence)
When is downwelling induced?
- When nearshore surface water is driven landward
- When gyre converge (Ekman convergence)
What is Langmuir circulation?
- Horizontal, helical motion of water
- Created when wind blows more than 3.5ms-1
- Flows paralle to the generating wind
- Creates alternate zones of convergence and divergence
- Forms sea stripes (material that collects in bands parallel to wind direction)
Where do ocean mounds form?
In the centre of gyres where Ekman transport of water convergences
What is geostrophic current?
The circulation of water around ocean mounds due to a balance between pressure gradient force and Coriolis
What way do gyres rotate in the N and S hemisphere?
Clockwise in the N hemisphere and Anticlockwise in the S hemisphere
What are currents like along the western edge of basins?
Narrow, deep and swift (e.g. Gulf Stream)
What are currents like along the eastern edge of basins?
Broad, shallow and slow (e.g. Canary current)
What is western boundary intensification?
The geostrophic mound of water is deflected to the western part of the ocean basin because of the eastward rotation of the earth on its axis
What % of currents are driven by winds? by density?
- 10% by winds
- 90% by density
What is the Sargasso Sea?
Large lens of warm water that circulates clockwise around the North Atlantic gyre; it is separated from cold water below and to the sides by a strong thermocline
What is a warm core ring?
A meander that has broken free from a gyre and encloses a mass of warm water
What is a cold core ring?
A meander than has broken free from a gyre and encloses a mass of cold water
How wide and deep are cold wand warm core rings?
100-300 km in diameter and 3 km, or less, thick
How quickly do the cold and arm core rings rotate?
1 ms-1
Typically, how many warm and cold rings are generated form the Gulf stream each year?
- 8 warm rings
- 10 cold rings
What is the Sargasso Sea named after?
The brown sea weed, Sargassum, that is found there
