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Atmospheric Stability

Atmospheric Stability. The resistance of the atmosphere to vertical motion. Stable air resists vertical motion Unstable air encourages vertical motion. ↓ pressure (expansion) ↑ volume = cooling. Air Falling. Air Rising. ↑ pressure (compression) ↓ volume = warming.

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Atmospheric Stability

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  1. Atmospheric Stability • The resistance of the atmosphere to vertical motion. • Stable air resists vertical motion • Unstable air encourages vertical motion

  2. ↓ pressure (expansion) ↑ volume = cooling Air Falling Air Rising ↑ pressure (compression) ↓ volume = warming

  3. Dry adiabatic lapse rate (unsaturated air) • Lapse rate – change in temperature with elevation • Adiabatic process: - No heat is gained or lost by mixing with the surrounding air (“parcels of air”) • Dry adiabatic lapse rate = 5.5°F/1000 ft

  4. Moist-adiabatic Rate(saturated air) • Air rises and cools – if dew point reached, condensation occurs • Energy released with condensation → warming • Lapse rate reduced to 3°F/1,000 ft • Parcel becomes warmer than surrounding air – continues to rise (free convection) • Eventually reaches colder air aloft – cools and stabilizes at new level

  5. SOUNDING – Atmospheric Temperature Inversion • Moist adiabatic lapse rate • May become unstable if air becomes • warmer than surrounding area and • continues to rise • Dry adiabatic lapse rate (stable) • resists vertical motion • parcel will remain in position • Super adiabatic lapse rate • Lapse rate > dry-adiabatic rate • Example: Strong heating of ground surface • Warm air below cool air

  6. How is air lifted in the atmosphere? • Thermal lifting (convection) • Orographic lifing • Frontal lifting

  7. What is the stability of the air?

  8. What is the stability of the air?

  9. TTYP • Read the material independently (2 min) • One person explains the material – the other person listens (3 min) • The “listener” adds to the explanation any information that they believe would help to improve their understanding of it. (2 min) • Both people decide on the best explanation that they both agree with. (2 min) • Both should be prepared to share the information with the entire class.

  10. Night Inversion

  11. Air near Earth’s surface cools at night (radiation, conduction, convection) Cold air flows downward Layer of warm air above = thermal belt Inversions strongest when atmospheric conditions = stable, calm Clouds & water vapor reduce outgoing radiation Wind causes air layers to mix Surface heating during day – cause inversion to break = severe fire conditions Night inversion

  12. Marine inversion

  13. Subsidence Inversion

  14. Subsidence & mountain waves(& foehn winds)

  15. Signs of a Stable Atmosphere

  16. Signs of an Unstable Atmosphere

  17. Marine inversion Night Inversion Subsidence Inversion

  18. Subsidence & mountain waves (& foehn winds) Signs of an Unstable Atmosphere Signs of a Stable Atmosphere

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