Pressure Belts - Grade 11 Geography

Pressure Belts

Prerequisites

  • Warm air rises and has low pressure.
    • Warm air moves up into the upper atmosphere, potentially forming clouds.
  • Cold air descends and has high pressure.
    • Cold air moves from the clouds to the ground.

Equatorial Low Pressure Belt (0° Latitude)

  • Located at the equator.
  • Characterized by warm air rising, leading to low pressure.
  • Formation: Intense heating of warm, moist air due to direct insolation (sun rays) at the equator.
  • When warm air rises, it condenses and forms clouds, leading to rainfall.

Subtropical High Pressure Belt (30° Latitude)

  • Located at 30° latitude.
  • Characterized by cold air descending, leading to high pressure.
  • Formation: Cold air subsides (descends) from the upper atmosphere to the 30° latitude.
  • Cold air descending does not result in cloud formation. As it descends, it heats up but does not condense.
  • Little to no rainfall expected in this region.

Subpolar Low Pressure Belt (60° Latitude)

  • Located at 60° latitude.
  • Characterized by warm air rising, leading to low pressure.
  • Significant because two air masses converge here:
    • Warm air from the 30° latitude.
    • Cold air from the 90° latitude (Poles).
  • The meeting point is characterized by a front which separates warm and cold air.

Polar Front

  • Definition: A boundary that separates warm and cold air masses.
  • At 60° latitude, the front is the polar front.
  • The subpolar low pressure belt consists of:
    • Cold, dry air from the polar region (90° latitude).
    • Warm, moist air from the subtropical belt (30° latitude).
  • Weather conditions at the subpolar low pressure belt are contrasting due to the presence of both cold and warm air, leading to variable rainfall conditions.

Polar High Pressure Belt (90° Latitude)

  • Located at the poles (90° latitude).
  • Characterized by cold, descending air, leading to high pressure.
  • Formation: Low temperatures at the poles due to less sunlight (insulation).
  • Low temperatures cause the air to be cold and sink.
  • Little to no rainfall due to the absence of rising warm air.