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Oceanography > Surface currents - 6 > Flashcards

Surface currents - 6 Flashcards

1
Q

Why does equatorial low pressure occur?

A
  • intense heating
  • high moisture content
  • rising air here
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2
Q

Why does polar high pressure occur?

A
  • cold, dry dense air sinking

- creates an area of divergence at the surface

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3
Q

What is Coriolis deflection?

A

The apparent deflection of objects moving across Earth’s surface

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4
Q

Where is the maximum rotational velocity of the earth?

A

At the equator

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5
Q

Where is the minimum rotational velocity of the earth?

A

At the poles

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6
Q

Why does a zonal wind system develop?

A

Due to unequal surface heating and Coriolis deflection

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7
Q

What are the doldrums?

A

A belt around the earth near the equator with low pressure due to rising air here

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8
Q

What are the horse latitudes?

A

Latitudes around 30º where cooler and dense air sinks

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9
Q

What latitude does the Ferrel extend to?

A

30º to 50º

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10
Q

What latitude does the polar cell extend to?

A

50º to 900

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11
Q

What produces wind driven ocean currents?

A

Frictional interaction between wind and water

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12
Q

How does the speed of the wind and the induced current differ?

A

The induced ocean current is about 3-4% of the velocity of the wind

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13
Q

What are zonal wind flows?

A

Winds that move nearly parallel to latitude as a result of the Coriolis deflection

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14
Q

What generates westward ocean currents?

A

Easterly trade winds

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15
Q

What generates eastward ocean currents?

A

Westerly trade winds

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16
Q

How are gyres created?

A

Westward and eastward driven ocean currents are deflected by continents, creating a circular flow around basins

17
Q

What height difference is observed over the ocean surface, from mounds to depressions?

A

1 metre

18
Q

How are ocean mounds formed?

A

Due to convergences where water sinks (downwelling)

19
Q

How are ocean depressions formed?

A

Due to divergences where water rises (upwelling)

20
Q

What is the Ekman Sprial?

A

The resultant pattern caused by changes in current direction and speed with depth

21
Q

What is Ekman transport?

A

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

22
Q

What effect does Ekman transport have at the coast?

A

Can induced upwelling or downwelling

23
Q

When is upwelling induced?

A
  • When nearshore surface water is driven seaward

- When gyres diverge (Ekman divergence)

24
Q

When is downwelling induced?

A
  • When nearshore surface water is driven landward

- When gyre converge (Ekman convergence)

25
Q

What is Langmuir circulation?

A
  • 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)
26
Q

Where do ocean mounds form?

A

In the centre of gyres where Ekman transport of water convergences

27
Q

What is geostrophic current?

A

The circulation of water around ocean mounds due to a balance between pressure gradient force and Coriolis

28
Q

What way do gyres rotate in the N and S hemisphere?

A

Clockwise in the N hemisphere and Anticlockwise in the S hemisphere

29
Q

What are currents like along the western edge of basins?

A

Narrow, deep and swift (e.g. Gulf Stream)

30
Q

What are currents like along the eastern edge of basins?

A

Broad, shallow and slow (e.g. Canary current)

31
Q

What is western boundary intensification?

A

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

32
Q

What % of currents are driven by winds? by density?

A
  • 10% by winds

- 90% by density

33
Q

What is the Sargasso Sea?

A

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

34
Q

What is a warm core ring?

A

A meander that has broken free from a gyre and encloses a mass of warm water

35
Q

What is a cold core ring?

A

A meander than has broken free from a gyre and encloses a mass of cold water

36
Q

How wide and deep are cold wand warm core rings?

A

100-300 km in diameter and 3 km, or less, thick

37
Q

How quickly do the cold and arm core rings rotate?

A

1 ms-1

38
Q

Typically, how many warm and cold rings are generated form the Gulf stream each year?

A
  • 8 warm rings

- 10 cold rings

39
Q

What is the Sargasso Sea named after?

A

The brown sea weed, Sargassum, that is found there

Oceanography (13 decks)

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