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Stability & Instability
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Stability & Instability

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Mass movement (Paper 1)

Mass movement (Paper 1)

Published in: Business, Technology

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  • 1. Stability & Instability
  • 2. Does forced uplift trigger continued uplift?
    • Yes - unstable atmosphere
    • No - stable atmosphere
    • Does rising air cool more or less rapidly than environment it is rising through?
    • Cooler parcel -> denser -> sinks back toward initial position
    • Warmer parcel -> lighter -> continues rising
  • 3. Parcel cooling rate depends only on whether parcel is saturated or not
    • Unsaturated parcel cools at constant dry adiabatic lapse rate (DALR) - no condensation occurring
    • Nearly constant at 1.0C / 100m
    • Saturated parcel cools at slower saturated adiabatic lapse rate (SALR) condensation is occurring
  • 4. Unsaturated parcel cools at constant dry adiabatic lapse rate (DALR)
  • 5.
    • Saturated parcel cools at slower saturated adiabatic lapse rate (SALR) condensation is occurring
      • Condensation releases latent heat into atmosphere, reducing rate of cooling
    • Typical value of about 0.6C / 100m
  • 6. Saturated parcel cools at slower saturated adiabatic lapse rate (SALR)
  • 7. Environmental lapse rate (ELR)
      • Vertical change in temperature moving through a free atmosphere
      • Highly variable, depends on many different factors
  • 8. Adiabatic processes
    • Adiabatic processes are reversible
    • Adiabatic processes in atmosphere mainly related to vertical motion
    • Vertical motion subjects air parcels to changes in pressure
    • Rising air parcels expand due to reduced pressure and cool
    • Sinking air parcels contract due to increased pressure and warm
  • 9. Stability
    • ELR < SALR
    • Rising parcel always cools more rapidly than environment
    • Becomes denser than the environment and sinks
    • Environment becomes more stable when lower levels cooled or upper levels warmed
  • 10.  
  • 11. Instability
    • Absolute instability: DALR < ELR
    • Rising parcel always cools more slowly than environment
    • Becomes less dense than environment and continues to rise
  • 12.  
  • 13. Conditional instability
    • Conditional instability: SALR < ELR < DALR
    • Unsaturated parcel cooling at DALR cools more rapidly than environment
    • Saturated parcel cooling at SALR cools more slowly than environment
    • Stability or instability conditional on whether parcel is saturated or not
  • 14.  
  • 15. Summary .