PHAK Chapter 12 Weather Theory

Composition of the Atmosphere

• Atmosphere consists of 78% nitrogen, 21% oxygen, and 1% other gases.

Layers of the Atmosphere

• The atmosphere is divided into four layers: troposphere, stratosphere, mesosphere, and thermosphere.

Troposphere

• The lowest layer extends up to approximately 20,000 feet.
• Most weather phenomena, clouds, storms, and temperature changes occur here.
• Average temperature decreases by about 2°C for every 1,000 feet of altitude gained.
• Atmospheric pressure decreases by one inch for every 1,000 feet in altitude.

Tropopause

• Acts as a boundary between the troposphere and stratosphere.
• Traps moisture and associated weather patterns within the troposphere.

Stratosphere

• The second-lowest atmospheric layer, spanning from the tropopause up to 160,000 feet.
• Characterized by stable air and minimal weather activity.

Mesosphere

• Lies immediately above the stratosphere.
• Exerts little influence on weather conditions.

Thermosphere

• The uppermost layer of the atmosphere, extending above the mesosphere.

Atmospheric Circulation

• Involves movement of air across the Earth's surface, driven by uneven heating.
• Warm air rises and is replaced by cooler air, creating circulation patterns.
• Warm air moving toward the poles cools, becomes denser, and sinks back to the surface.

Atmospheric Pressure

• Changes in air pressure are influenced by irregular heating of the Earth's surface.
• Pressure varies with altitude, temperature, and air density.

Coriolis Force

• Deflects moving air due to Earth's rotation: to the right (clockwise) in the Northern Hemisphere, and to the left (counter-clockwise) in the Southern Hemisphere.
• Creates distinct atmospheric circulation cells in each hemisphere, influencing trade winds and weather patterns.

Wind and Currents

• Air moves from high to low pressure areas, seeking lower pressure.
• Includes convective currents (upward and downward) and horizontal wind movement.

Wind Patterns

• In the Northern Hemisphere, air moves from high-pressure areas, deflected right, forming anticyclonic circulation.
• Air flowing toward low-pressure areas creates counterclockwise cyclonic circulation.

High Pressure Systems

• Characterized by dry, descending air.
• Generally associated with clear and good weather conditions.

Low Pressure Systems

• Air converges into low-pressure areas, replacing the rising air.
• Tends to bring cloudiness and precipitation, associated with poor weather.

Convective Currents

• Uneven heating from different land types causes local circulation:
  • Plowed ground and barren land heat quickly, generating updrafts.
  • Water and vegetated areas absorb heat slowly, creating downdrafts.

Sea Breeze

• Cooler air from over oceans/lakes flows toward land.
• Land heats faster than water, causing air over land to rise, drawing in cooler air from the water.

Test your knowledge of weather theory with this quiz focused on the atmospheric composition and its layers. Review key concepts like the types of gases in the atmosphere and the characteristics of each atmospheric layer. Ideal for students studying aviation or meteorology.