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OS102 > Wind-driven circulation > Flashcards

Wind-driven circulation Flashcards

1
Q

What is the basis of global wind circulation?

A
  1. High solar radiation INPUT at equator
  2. Causes the air (surface of air) to warm
  3. Warm air expands upwards (and outwards) and become sufficiently warm enough to become buoyant = LOW DENSITY which tends to be pushed upwards
  4. Air upwards = high pressure which drives the air outwards towards the poles
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2
Q

What is true of the Earth’s rotation ion terms of global winds?

A

Earth’s rotation (spin on axis) produces strong modification of large-scale movements of air and water

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3
Q

What is the coriolis effect?

A

Objects/material moving relative to found are deflected from ‘expected’ path

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4
Q

What way is circulating air deflected in the Northern hemisphere? (Coriolis effect)

A

Right

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5
Q

What way is circulating air deflected in the Southern hemisphere? (Coriolis effect)

A

Left

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6
Q

How many circulation cells are there per hemisphere?

A

3

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7
Q

What are the 3 circulation cells in each hemisphere?

A
  1. Hadley cell
  2. Ferrell cell
  3. Polar cell
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8
Q

What is true of the hadley cell?

A
  • Low latitude overturning circulation
  • Airflow equator-wards
  • 0-30°C
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9
Q

What is true of the Ferrell cell?

A
  • Mid-latitude atmospheric circulation cell
  • Between 30-60°C
  • Surface flow is polarwards
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10
Q

What is true of the polar cell?

A
  • Air in these cells sink over highest latitudes and flow outwards toward lower latitudes at the surface
  • 60-90°C
  • Airflow equator-wards
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11
Q

What are doldrums?

A

(Between the 3 circulation cells) There are regions where air isn’t tending to move North/South or horizontally as it is the regions where the air is moving up or down more

History – ‘stuck in the doldrums’ – stuck/going slow = lack of influential wind

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12
Q

What direction do gyres circulate in the Northern hemisphere?

A

Clockwise

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13
Q

What direction do gyres circulate in the Southern hemisphere?

A

Counter-clockwise

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14
Q

What creates gyres?

A

Deflection by continents creates gyres

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15
Q

What is true of surface currents?

A

Surface currents are circulating water all the way round ocean basins

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16
Q

How does drag (surface currents) work?

A

Drag transfers momentum from air (wind) to water (current) through collisions between air and water as momentum transfer.

Fast moving air impacting with the surface gives up some of its momentum and causes water to start moving faster = wind moving slower = friction

17
Q

What is true of surface & deeper flow in terms of Ekman transport?

A

Surface flow is deflected relative to wind

Deeper flow shows greater deflection

18
Q

What is Ekman transport?

A

Ekman transport occurs when ocean surface waters are influenced by the friction force acting on them via the wind.

19
Q

What is the Ekman spiral?

A

Surface flow is 45° to wind (to right in N hemisphere)

Net flow is 90° to wind

At base of spiral, flow is opposite to wind

= Ekman transport

20
Q

What is Langmuir circulation?

A

Persistent winds can induce small-scale vertical motions
– 10-100m scale
– minutes-hours

Zones of convergence parallel to wind direction

Locations of accumulation of flotsam and foam

21
Q

What is the process of geostrophic flow?

A
  1. Ekman transport causes water to converge in centre of gyres
  2. Resulting mound of water produces balancing pressure-gradient force
  3. Steady state/equilibrium flow is called geostrophic flow – Coriolis and gravity (pressure) forces and balanced
22
Q

What are Western Boundary currents?

A

They are warm, deep, narrow, and fast-flowing currents that form on the west side of ocean basins due to western intensification.

Faster and narrower than currents on the Eastern side of an ocean

23
Q

What are Western Boundary currents due to?

A
  1. Increase in Coriolis effect with latitude
  2. Variation of east-west wind field
  3. Friction between currents and landmasses
24
Q

What are the 5 Western Boundary currents?

A
  1. Gulf Stream
  2. Brazil and Malvinas current
  3. Somali and Algulhas curent
  4. Kuroshio current
  5. EAC
25
Q

How are Gulf stream eddies form?

A

Gulf stream separates cold and warm water

the flow often meanders, and these meanders may ‘pinch off’ to form closed loops, spinning these ‘loops’ out into the ocean

OS102 (13 decks)

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