L15 Atmospheric Stability

1
L15 Atmospheric Stability

• Stability and lapse rate
• Stability on skew T ln p charts
• Stable, neutral, unstable, conditionally unstable
• Stable atmosphere
• Inversions fog/air pollution
• Unstable atmosphere
• Convection
• Thunderstorm development

2
Static stability of dry air
1st case Real lapse rate, G is less than the
DALR, Gd What happens to air at O that is
displaced upwards by a disturbance? And what
happens if it isdisplaced downwards?
See Wallace Hobbs section 3.6
3
Static stability of dry air
2nd case Real lapse rate, G gt Gd What happens
to air at O that is displaced upwards by a
disturbance? And what happens if it isdisplaced
downwards?
See Wallace Hobbs section 3.6
4
Useful analogy for stabilityball on a surface
Stable
Unstable
Neutral
Conditionalinstability
Unstable profilescannot persist, sotend to
rapidlyevolve to be neutral
5
Stability and air pollution
Match the plume dispersionpattern to the
temperatureprofiles below
Atmospheric temperature profileis the solid
line.Dry adiabat is dashed line.
6
Stability and air pollution
Neutral profile smokegoes anywhere
Stable profile smokestays at emitted height
Stable above, neutralbelow smoke mixes down
but not up
Neutral above, stablebelow smoke mixes up but
not down
Atmospheric temperature profileis the solid
line.Dry adiabat is dashed line.
7

• Stability on skew T-ln p diagram

stable
8
Absolutely unstable example
Tiny unstable layer near ground
9

• Extreme example of instability a forest fire

Any form of strong heating of the ground can
cause instability
10
Inversion layer example
Very stable layerprobably definingthe top of
the boundary layer. Very stable layerswhere
temperatureincreases with heightare called
inversions. Top of the BL oftencapped by
aninversion tends totrap pollution in BL
11
Edinburgh, c 1950 auld reekie
London, 1952
12
Buncefield oil depot fire, 2005
13
(No Transcript)
14
(No Transcript)
15
Satellite image at 1045 GMT,5 hours after start
of fire
16
Nottingham Skew T-log P on day of Buncefield Fire
(12Z, 11 Dec 2005)
Strong inversionnear ground
17
(No Transcript)
18
South PoleNote it is cold!!Surface pressure
isonly 700 hPaVery stable thinlayer close to
surface

• Scott-Amundsen South Pole station

19
Kuching Indonesia
20
Conditionally unstable - tropics
21
Small scale cumulusclouds typical
ofconvection and anunstable tropicalatmosphere.
In the tropics theseclouds typically build up
during the day to cumulonimbusas surface
heatingincreases theinstability.

• Douala, Cameroon
• (Image from Google earth)

22
Summary

• Stability and lapse rate
• Stability on skew T ln p charts
• Stable, neutral, unstable, conditionally unstable
• Stable atmosphere
• Inversions fog/air pollution
• Unstable atmosphere
• Convection
• Thunderstorm development more next time