The atmosphere is like a layered blanket around Earth, each layer with its own personality. From the weather-filled troposphere to the protective ozone-rich stratosphere, these layers play crucial roles in our planet's climate and habitability.

Understanding the atmosphere's structure helps us grasp how it shields us from harmful radiation and regulates temperature. As we explore each layer's unique characteristics, we'll see how they work together to create Earth's life-supporting environment.

Atmospheric Layers

Lower Atmospheric Layers

• Troposphere extends from Earth's surface to ~12 km (7.5 miles) high
  • Contains 75-80% of the atmosphere's mass and 99% of its water vapor
  • Temperature decreases with height at a rate of ~6.5°C/km (lapse rate)
  • Most weather phenomena occur in the troposphere (clouds, precipitation, storms)
• Stratosphere extends from the tropopause to ~50 km (31 miles) high
  • Temperature increases with height due to absorption of UV radiation by ozone
  • Ozone layer is located within the stratosphere at ~15-35 km high
  • Relatively stable layer with little vertical mixing
  • Contains the ozone layer which absorbs harmful UV radiation

Upper Atmospheric Layers

• Mesosphere extends from the stratopause to ~85 km (53 miles) high
  • Temperature decreases with height, reaching a minimum at the mesopause
  • Noctilucent clouds can form at the mesopause during summer at high latitudes
  • Meteors typically burn up in the mesosphere due to friction with air molecules
• Thermosphere extends from the mesopause to ~600 km (373 miles) high
  • Temperature increases with height due to absorption of high-energy radiation
  • Auroras (northern and southern lights) occur in the thermosphere
  • Highly rarefied air with low density and pressure
• Exosphere is the outermost layer, extending from the thermopause to ~10,000 km
  • Extremely low density with particles rarely colliding
  • Atoms can escape Earth's gravity and enter space
  • Satellites in low Earth orbit travel through the exosphere (ISS at ~400 km)

Atmospheric Characteristics

Vertical Temperature Structure

• Temperature inversion occurs when temperature increases with height in a layer
  • Inversions occur in the stratosphere and thermosphere due to absorption of radiation
  • Inversions create stable layers that resist vertical mixing
• Ozone layer absorbs UV radiation in the stratosphere, causing a temperature inversion
  • Ozone (O3) is formed by photochemical reactions involving UV light and oxygen
  • Ozone layer protects life on Earth's surface from harmful UV radiation

Pressure and Density Variations

• Atmospheric pressure decreases exponentially with height
  • Pressure at sea level averages ~1013 millibars (mb) or 101.3 kilopascals (kPa)
  • Pressure decreases by half for every ~5.5 km increase in altitude
  • Lower pressure at higher altitudes affects breathing, cooking, and boiling points
• Density gradient in the atmosphere, with density decreasing rapidly with height
  • Density is highest near Earth's surface due to compression by the air above
  • Density decreases from ~1.225 kg/m^3 at sea level to ~0.02 kg/m^3 at 30 km high
  • Lower density at higher altitudes affects aircraft performance and aerodynamics