Static Stability/ Atmospheric Stability (Meteorology)

[Ref Understanding Weather & Climate, Books a la Carte Edition (6th Edition) #ISBN-13: 978-0321773227 #ISBN-10: 0321773225 CH 6 Cloud Development and Forms, Pilot’s Handbook of Aeronautical Knowledge, FAA-H-8083-25B Page 12-13]

Static stability (a.k.a Atmospheric Stability) – is the susceptibility of air to uplifts, which depends on its ability to resist vertical motion. In short, the stability of the air is determined in combination of moisture and temperature.

  1. Static stable air
    – resists upward displacement as well as sink back to its original level when the lifting mechanism ceases
  2. Static unstable air
    – becomes buoyant when lifted and continues to rise if given an initial upward push
  3. Static neutral air
    – neither rises nor sink, simply rest at the height where it was displaced.

Notes:
static unstable – (warm) air is less dense than the air around it, it has positive buoyancy
static stable – (cold) air is more dense than the air is around it, it has negative buoyancy 


Since DALR (1°C/100m ≈ 3°C/1000 feet) > SALR (0.5°C/100m ≈ 1.5°C/1000 feet) – There are 3 cases:

  1. ELR > DALR > SALR – Absolutely unstable
    occur because parcel of air always warmer than the air around it, leading to positive buoyancy – regardless of whether the air is unsaturated or saturated
  2. DALR > SALR > ELR – Absolutely stable
    occur because the parcel of air always cooler than the surrounding air, leading to a negative buoyancy regardless of  whether the air is unsaturated or saturated
  3. DALR > ELR > SALR – Conditionally unstable
    occur if the parcel of air is lifted about some critical altitude (level of free convection), it will become buoyant and rise on its own due to static unstable (with positive buoyancy) – warmer than the air around it.
    (p.S – level of free convection  Lifting condensation level (LCL)

 

#atmospheric stability #met

Read More:

Limitations on the lifting of unstable air – how unstable air be stopped to be lifting?

  1. Layer of stable air (inversion)
    • Where the parcel of air cools more rapidly than the ambient air and eventually become cooler than its surroundings
  2. Entrainment
    • is the process that especially active along the edges of growing clouds
    • to suppresses the growth of clouds by reduce the buoyant
      • draw the ambient unsaturated air into the parcel at their margin, and thus causes some of the liquid droplets to evaporate – consumes latent heat and thereby cools the margin of the cloud

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