The General Circulation

Question 1

Explain what is meant by ‘the general circulation’.

Answer 1

• The large-scale pattern of pressure systems and winds, which endure throughout the year
• The factors that control transfer of heat around the world and constant angular momentum and vertical/horizontal circulations

Question 2

Explain why the polar highs exist.

Answer 2

• Air cools down and contracts at the poles
• Increases pressure at the surface creating a polar high

Question 3

Explain why polar easterlies exist.

Answer 3

• Coriolis force bends winds to the left in the southern hemisphere
• Wind flowing out from a high is anticlockwise for this reason and creates the polar easterlies to the north of them

Question 4

Explain why polar lows exist.

Answer 4

• Air becomes warmer as it moves away from poles and starts to rise
• Creates surface polar lows at 60 degrees N/S

Question 5

Explain why polar fronts exist.

Answer 5

• Formed when colder polar air meets warmer sub-tropical air
• This mixes around a low and creates warm and cold fronts

Question 6

Explain why mid-latitude westerlies exist.

Answer 6

• Coriolis force from the mid-latitude high rotates anticlockwise
• Causes winds to be westerlies to the south of them

Question 7

Explain why mid-latitude anticyclones exist.

Answer 7

• Upper air flows outwards from the equator towards the poles and from temperate latitude towards the equator
• This creates an excess of air at the tropopause in subtropical regions which is forced to descend.
• This creates the subtropical high pressure systems which are permanent features over the subtropical oceans at 30 degrees N/S

Question 8

Explain why sub-tropical trade winds exist.

Answer 8

• Caused by Coriolis effect deflecting air from the high
• North of the high become a SE in the southern hemisphere
• The reason it is not a complete easterly wind is because Coriolis effect reduces towards the equator

Question 9

Explain why the equatorial trough exists.

Answer 9

• Air is very warm at the equator surface and rises
• Reduces pressure at the surface created low pressure systems
• Trade winds converging from the north and south of the equator also forces air to rise as it meets creating narrow band of intense convection

Question 10

State the dominant factors that control the transfer of heat around the globe.

Answer 10

• Short wave solar radiation and long wave terrestrial radiation
• Conduction from Earth’s surface to 10cm up
• Convection for vertical transfer of heat there after
• Advection through wind/systems

Question 11

State the dominant factors that control the transfer of heat around the globe.

Answer 11

• Release of latent heat during cloud development
• General circulation which is constantly trying to correct the temperature imbalance between the equator and poles
• The seasons
• Sea currents

Question 12

Explain what is meant by ‘zonal index’.

Answer 12

• Strength of pressure gradient between 35 degrees S and 55 degrees S and is mirrored in the northern hemisphere
• Measures the strength of the upper level mid-latitude westerly geostrophic wind

Question 13

Explain what is meant by ‘zonal winds’.

Answer 13

• Refers to if the wind is positive (a westerly)
• Or negative (an easterly)

Question 14

Describe ‘high zonal index’.

Answer 14

• Suggests a strong pressure gradient from north to south
• Anticyclone will be to the north and depression will be to the south.
• Creates strong westerlies

Question 15

Describe ‘low zonal index’.

Answer 15

• Depression will be to the north and anticyclone will be to the south.
• Creates easterlies
• Pressure gradient is now negative from 35 degrees S to 55 degrees S

Question 17

State how ‘high zonal index’ and ‘low zonal index’ relate to the speed and direction of low tropospheric weather systems.

Answer 17

• All systems move west to east due to the rotation of the Earth
• High zonal index cause systems to move rapidly from west to east as the westerly increases their horizontal speed
• Low zonal index cause systems to move slowly from west to east or stop completely creating clocking highs

Question 18

State how the ‘high zonal index’ and ‘low zonal index’ relate to the strength and uniformity of upper-level westerlies and jet-streams.

Answer 18

• Stronger and more uniform with high zonal index
• Weaker and less uniform with low zonal index

Question 19

Define long atmosphere waves.

Answer 19

• AKA Planetary Waves or Rossby Waves
• Naturally occurring waves which form in rotating fluid
• Migrate west to east like a giant river that the jet-streams flow down
• Long waves have 1-3 wavelengths and transport warm air from the tropics to the poles and cold air to the tropics

Question 20

Define medium atmospheric waves.

Answer 20

• 4-7 wavelengths around the planet in size
• Responsible for high, lows, fronts, tropical cyclone and warm/cold pools

Question 21

Define short atmospheric waves.

Answer 21

• 8 wavelengths or greater and are short lived
• Cause gusts, thermals, local winds and rotor zone
• Where the waves are out of phase to each other they will cancel each other out

Question 22

Describe what is meant by ‘cold pool’.

Answer 22

• Occurs when long waves make large north south meanderings in a low zonal index situation
• Bubble of cold air in mid to upper troposphere moves from high latitudes to warmer lowers latitudes
• The cold pool is cut off and surrounded by warmer air
• Steepens ELR intensifying low pressure systems
• Originated from latitudes with permanent lows therefore carries those characteristics into the lower latitudes all the way to the surface
• Are associated with instability

Question 23

Describe what is meant by ‘warm pool’.

Answer 23

• Opposite of cold pool
• Bubble of warm air in mid to upper troposphere moves from low latitudes t colder higher latitudes
• Warm pool is cut off and surrounded by colder air
• Shallows ELR intensifying high pressure systems stability
• Originated from latitudes with permanent highs therefore carries those characteristics into the higher latitudes all the way to the surface.
• Associated with stability

Question 24

Describe the characteristics of maritime climates.

Answer 24

• Air mass created over then ocean
• Smaller changes in temperature relative to continental climate
• Air mass has relatively large amount of moisture in it
• Can be Polar, tropical or Equatorial regions

Question 25

Describe continental climates.

Answer 25

• Air mass created over the land
• Larger changes in temperature relative to maritime climate
• Air mass is relatively dry with low amounts of moisture
• Can be from Arctic/Antarctic, Polar, Tropical or Equatorial regions