Global air circulation patterns are caused by shifting high and low pressure zones that move seasonally in response to changes in the intensity of the Sun's rays between hemispheres. Unequal heating of the atmosphere causes warm air to rise at the equatorial low pressure belt, creating circulation cells that transport thermal energy to the polar regions which have pressure defects. Major pressure belts include the equatorial low, subtropical high pressure zones between 20-35 degrees north and south latitude driven by descending air, and subpolar low pressures near 60-70 degrees driven by the Coriolis effect.

1. GLOBAL AIR
CIRCULATION

2. LEARNING OUTCOMES
• Explain the meaning of pressure belts and how they move in different hemisphere
• Explain the causes and characteristics of global pressure belts
• In groups of 5 learners should present a 5 minute oral presentation explain the
relationship between temperature ,atmospheric pressure and wind

3. AIR CIRCULATION IN RESPONSE TO
UNEQUAL HEATING OF THE ATMOSPHERE
• Global air circulation systems moves thermal energy ,air and water from equatorial
regions with energy surpluses to the polar regions with energy defects.
• World pressure belts
• The global air circulation patterns control our weather and climate. These patterns are
caused by shifting zones of high or low pressure in summer and winter.
• They move seasonally with the varying intensity of the Sun’s direct rays.
• Atmospheric pressure is shown on maps by isobars which are lines joining places
with equal pressure.

4. WHERE ARE PRESSURE BELTS FOUND IN
EACH HEMISPHERE

5. SUMMARY OF THE CAUSES AND CHARACTERISTICS OF GLOBAL
PRESSURE BELTS
Name Location Causes Air characteristics
Equatorial low pressure 10° N to 10° S Thermal:
• Intense heating due to
constant high sun altitude
and consistent daytime
(12 hours) • Warming
creates less dense, lighter,
rising air.
Subtropical high pressure Between 20−35 °N and
20−35 °S
Dynamic:
• Air above region is
pushed downwards. • Air
heats by compression as
descends to Earth’s
surface.
Subpolar low pressure In the region of 60° and
70° to the north and
of the equator
Dynamic:
• As a result of the Earth’s
rotation, at these latitudes