Transcript Atmospheric Circulation And Motion - Geog

Atmospheric Circulation
And Motion
IB SL
The Tri-Cellular Model
• This shows how energy is redistributed across
the globe and ensures there is not a surplus at
the equator and deficit at the Poles.
• There are three major cells present: Hadley,
Ferrel and Polar. As shown on the two
diagrams below, the boundaries coincide with
particular latitudes.
• However, they do shift with the movement of
the Sun along with the ITCZ.
Intertropical Convergence Zone
• At the equator, trade winds meet and form the Winds are light and
known as the doldrums.
• Air is warm and unstable, having crossed warm oceans, and rises due to
convection currents.
• As the air rises it cools and large cumulonimbus clouds develop.
• The pressure at the equator is low.
• Eventually, the rising air has cooled to the same temperature as its
surroundings and begins to spread out.
• It falls at approximately 30 degrees north and south of the equator - the
descending limb of the Hadley cell. Pressure is high here.
• Air is now either returned to the equator at ground level, or travels to
the Poles as warm south-westerly winds. A
• t approximately 60 degrees north the air rises creating an area of low
pressure and the rising limbs of the Ferrel and Polar cells.
• It is here that the Polar front jet stream is located and depressions form.
Rossby Waves
• Rossby waves are high altitude, fast moving westerly
winds, which often follow an irregular path.
Jet Streams
• These exist within Rossby waves.
• They help in the rapid transfer of energy
around the globe, as they are very fast,
narrow bands of air that can reach speeds of
over 200km per hour.
• Five jet streams exist, with three having
significant importance:
Jet Streams
Jet stream:
Location:
Characteristics:
Divides the Ferrel and polar cells.
Gives wet or fine weather on Earth's
surface, and is strongly associated
with anticyclones and depressions.
Polar Front
40 degrees North and
South of the equator.
Subtropical
25-30 degrees North and
Divides the Hadley and Ferrel cells.
South of the equator.
Easterly
Equatorial
Equatorial regions.
A seasonal jet stream linked with the
Indian summer monsoon.
The Coriolis Force
This relates to the apparent deflection of winds to the right in
the northern hemisphere and the left in the southern
hemisphere due to the spinning of the Earth.
Pressure Gradient
Explains the movement of air between areas of high and low
pressure. Isobars show this phenomenon and the closer the
isobars, the stronger the winds. Winds act to balance out
differences in pressure, humidity and temperature.
Activity
Read through P224-228 in Geography An Integrated
Approach and answer the following questions...
1. What are the causes of the ITCZ and what weather
conditions are associated with it?
2. Why does the ITCZ move with the seasons?
3. What is the Jet Stream and how is it associated with
ground-level weather conditions?