Global Air Circulation

Question 1

ITCZ

Answer 1

Inter tropical convergence zone

The zone between the tropics (23 N and South of the equator), where warm, moist air from the subtropical high pressure belts converges

Question 2

Convergence

Answer 2

The inward flow of air to a low pressure

Question 3

Divergence

Answer 3

The outward flow of air from a high pressure

Question 4

Dew point temperature

Answer 4

The temperature at which air becomes saturated by cooling

Question 5

Jet stream

Answer 5

Strong winds blowing from west to east in the upper atmosphere 10km above the surface at speeds of 100-300km/hr

Question 6

Geostrophic wind

Answer 6

Blows parallel to isobars under the combined effects of the pressure gradient force and the coriolus force

Question 7

Föhn

Answer 7

Dry, hot wind that originates in a mountainous area

Question 8

Adiabatic

Answer 8

A change in temperature through a change in pressure only (or significant changes in altitude

Question 9

Relative humidity

Answer 9

A measure of the water vapor constant of air at a given temperature (it is expressed as a percentage)

Question 10

How are winds caused?

Answer 10

Winds are caused by the unequal heating of the earth’s atmosphere which results in the pressure belts

Question 11

Dynamic

Answer 11

Not directly because of the sun

Question 12

Thermal

Answer 12

Direct result of sun and temperature

Question 13

How do high and low pressure cells form?

Answer 13

During the day, the land heats up more quickly than the sea.
The air becomes less dense, expands and rises which results in a low pressure over the land.
Over the cooler sea the air is cooler so more dense, contracts and descends.
In this way high and low pressure cells form.

Question 14

What is wind?

Answer 14

Movement of air from places of higher pressure to places of lower pressure.

Question 15

Describe atmospheric pressure and wind

Answer 15

Hot air rises and cooler air flies in to replace it.
The convergence of two air masses will cause air to rise.
Air diverges and moves in opposite directions.

Question 16

Describe Jet streams

Answer 16

Strong winds blowing from west to east in the upper atmosphere about 10km above the surface.
They blow at speeds of about 100-300km/hr
The sub-tropical jet stream forms the boundary between the Hadley and Ferrel cells while between the polar and Ferrel cells we find the polar front jet stream.

Question 17

What is the pressure gradient force?

Answer 17

The rate at which pressure changes over a horizontal distance measured from high to low.
The pressure gradient is always at right angles to the isobars.

Question 18

Isobars…

Answer 18

Closer-steeper PGF, stronger wind speed
Further-weaker PGF, weaker wind speed

Question 19

Describe primary circulation

Answer 19

If the earth did not rotate on its axis then there would be simple form of pressure belts and wind circulation.
Low pressure at equator-hot/moist
High pressure at poles-cold/dry

Question 20

Describe secondary circulation

Answer 20

Because earth rotates on its axis, pressure belts aren’t simple.

Question 21

Air mass characteristics

Answer 21

Temperature and humidity characteristics of air masses are picked up from the surfaces over which they develop, so an air mass developing over the sea produces wet/moist, maritime air.
An air mass developing over land results in dry, continental air.

Question 22

Describe the global pressure belts with the seasons (situation of ITCZ)

Answer 22

South in December/January when southern hemisphere has summer

North in June/July when northern hemisphere has summer

In January ITCZ mostly situated South of equator
In July will shift North of equator

Question 23

Discuss the sub-tropical HP belt in the southern hemisphere

Answer 23

It is not a band but separate cells because of the large open ocean surfaces

Question 24

HIGH pressure cells in southern hemisphere

Answer 24

Sinking or descending
Anti-clockwise
Outward
Descending air is heated by compression
Fine weather (no rain, hot, dry)

Question 25

LOW pressure cells in southern hemisphere

Answer 25

Ascending, rising air
Clock-wise
Converging
Rising air cools by expansion
Rising air cools and condenses resulting in rain, cool temperature, cloudy weather