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Atmospheric Stability. Stability of Atmosphere is affected by. Temperature of the surrounding environment Temperature of the air parcel. Altitude. 0. 0. Temperature. Environmental Lapse Rate (ELR). 6 o C/1,000m. Altitude. 0. 0. Temperature. Isothermal Lapse Rate. Altitude (km). 0.

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Presentation Transcript
stability of atmosphere is affected by
Stability of Atmosphere is affected by
  • Temperature of the surrounding environment
  • Temperature of the air parcel
conditions for radiation inversion
Conditions for Radiation Inversion
  • At night
  • Clear sky
  • Calm condition
  • Relatively dry air
  • Snow cover

Radiation loss

Ground

air drainage inversion

Cold air of higher density

Cold air of higher density

Warm air

Air drainage inversion
  • In a valley
  • At night
frontal inversion

Warm air mass

INVERSION

Cold air mass

Frontal Inversion

Ground

adiabatic lapse rate
Adiabatic lapse rate
  • Adiabatic cooling
  • Decrease in temperature without heat exchange with surrounding air
  • When an air parcel is forced to rise,
  • It expands due to the lower air pressure of surrounding air
  • Increase of volume leads to decrease in temperature
dry adiabatic lapse rate
Dry adiabatic lapse rate
  • DALR
  • Temperature change of dry air mass
  • 1oC/100 m
saturated adiabatic lapse rate
Saturated adiabatic lapse rate
  • SALR - Temperature change of air mass when condensation occurs
  • 6oC/1,000 m in usual cases
  • SALR depends on
  • Moisture content & temperature
  • Higher moisture content leads to smaller lapse rate
  • SALR is smaller when temperature is lower
absolutely unstable air

Altitude

DALR

SALR

ELR

0

0

Temperature

Absolutely Unstable Air

ELR% > DALR > SALR

absolutely unstable air1

Altitude

ELR

0

0

Temperature

Absolutely Unstable Air

SALR

ELR% > DALR > SALR

Condensation level

DALR

absolutely unstable air2
Absolutely Unstable Air
  • ELR% > DALR > SALR
  • Therefore, the rising air parcel is always hotter than the surrounding air
  • The density is lower
  • Further upwards displacement is resulted
  • For a sinking air parcel, further downwards displacement is resulted
conditionally stable unstable air

Altitude

SALR

DALR

0

0

Temperature

Conditionally Stable / Unstable Air

ELR

DALR> ELR > SALR

conditionally stable unstable air1
Conditionally Stable / Unstable Air
  • DALR > ELR
  • Means the air parcel is cooler than surrounding air
  • It will not rise if the external force discontinues
  • However, when condensation takes place
  • Latent heat is released
  • The air parcel cools more slowly : ELR>SALR
  • The air parcel will become warmer than surrounding air - Unstable
absolutely stable air

Altitude

SALR

DALR

0

0

Temperature

Absolutely Stable Air

ELR% < SALR < DALR

ELR

Air parcel tends to return to its original position

stability and cloud formation
Stability and Cloud formation
  • Instability leads to continuous rise of air parcel
  • Thick clouds such as cumulus and cumulonimbus will be formed
  • Stability will make rising air parcel go back to original position
  • Only thin clouds such as stratus
atmospheric stability and cloud development

Altitude

Cloud top

SALR

Condensation level

DALR

0

0

Temperature

Atmospheric stability and cloud development

ELR

Air parcel tends to rise because of higher temperature

reference website
Reference Website

www.piercecollege.com/offices/weather/stability.html

describe the change of elr
Describe the change of ELR
  • Below 250m, temperature increases with height causing a temperature inversion
  • From 250m upward, temperature generally decreased with increasing altitude at a rate about 12.4℃/1,000m
  • The ELR below 1,750m is greater than above, i.e. the temperature decreases more rapidly from 250m to 1,750m and less rapidly above 1,750m.
slide24

Dew point=5℃

DALR=10℃/1km

SALR=5℃

Condensation level

dew point
Dew point
  • Dew-point is reached at 1,500m
  • Condensation process takes place with the changing of water vapour into water droplets.
  • The development of rain clouds with a thickness of 2,100m
  • Freezing process ocurs with formation of ice crystals if freezing temperature is reached.
dew point1
Dew point
  • The coalescence of water droplets and ice crystals may induce precipitation
stability of air
Stability of air
  • Below 1,700m, the rising air parcel is colder, and hence denser, than its surrounding air. There is a tendency for the rising air to sink back to ground level. The air parcel is said to be stable.
  • The temperature inversion reinforces the stable condition.
stability of air1
Stability of air
  • As condensation process occurs at 1,500m with the release of latent heat, the rising air parcel cools less rapidly at the SALR.
  • From 1,700m upwards, the air parcel becomes warmer, and hence lighter, than its surrounding environment. It will become unstable and will continue to rise its own buoyancy
stability of air2
Stability of air
  • As a general, the rising air parcel is said to be conditionally unstable since it is stable when it is unsaturated but becomes unstable when saturated.
natural mechanism lead to uplift
Natural mechanism lead to uplift
  • Air movement encountering mountian barrier
  • Meeting of air masses with different properties along frontal surface
  • Convection uplift due to local heating
  • Convergence of air masses at a lower pressure zone
uplift in a highly urbanized environment
Uplift in a highly urbanized environment
  • Urban heat island promotes convective turbulence and the upward movement of air
  • Surface roughness due to the presence of high buildings enhances vertical air motion
slide32

22℃

24℃

28℃

26℃

Urban Heat Island

slide33
Urban heat island encourages condensation and cloud formation
  • However, high pressure in surrounding rural areas leads to closed circulation
  • Pollutants in urban can hardly diffused
  • Pollutants together with fog and cloud leads to the formation of smog
  • Pollution induced temperature inversion create stable condition which hinders diffusion of pollutants
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