Atmospheric Stability

• The resistance of the atmosphere to vertical motion.

• Stable air resists vertical motion• Unstable air encourages vertical motion

↓ pressure(expansion)↑ volume= cooling

AirRising

AirFalling

↑ pressure(compression)↓ volume= warming

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

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

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

Inversion

Super adiabatic lapse rate- Lapse rate > dry-adiabatic rate- Example: Strong heating of ground surface- Warm air below cool air

SOUNDING – Atmospheric Temperature

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

What is the stability of the air?

What is the stability of the air?

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.

Night Inversion

• 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

Marine inversion

Subsidence Inversion

Subsidence & mountain waves(& foehn winds)

Signs of a Stable Atmosphere

Signs of an Unstable Atmosphere

Night Inversion Marine inversion

Subsidence Inversion

Subsidence & mountain waves (& foehn winds)

Signs of a Stable Atmosphere Signs of an Unstable Atmosphere