Temperature Inversions
Why is the Earth’s Surface
Warm?
Some of the sun’s
energy is converted to
heat as it penetrates
the earth’s atmosphere
The radiant heat of the
sun also warms the
surface of the earth
NASA
Heating of Air
The warmed surface of the
earth heats the air just above it
in the troposphere by
convection
Troposphere = the lower atmosphere
that we live in
Some of the sun’s energy also
heats the air through
conduction and the rising of
warmed air (convection)
http://www.srh.noaa.gov/jetstream//atmos/heat.htm
Atmospheric Layers and
Temperature
As it rises, this warmed air
in the troposphere expands
and cools
Density of the air decreases
with the expansion of air,
making it ‘lighter’ in weight
http://www.srh.noaa.gov/jetstream//atmos/atmprofile.ht
m
Air Temperature in the Lower
Atmosphere
Air temperature in the troposphere
therefore gets cooler as altitude
increases
Temperature at earth’s surface= about
62°F/17°C
Temperature at about 12 miles altitude =
about 60°F/-51°C
Height of troposphere is approx. 12 mi. at
equator
Air Movement
As the warm air rises, cooler
air (more dense, therefore
heavier), rushes in to take its
place
This ‘vertical mixing’ is what
causes wind
Wikimedia Commons
Thermal column. The cloud (A) is above the ground. The sun increases
the temperature of the ground which will then warm the air above it (1).
The bubble of hot air starts to rise (2) and begins to cool as it expands
and moves upward into cooler air. Due to its lower temperature, the air
becomes cold enough to contract and then move downward (3) to
repeat the cycle.
What is a Temperature
Inversion?
A ‘Temperature Inversion’
occurs when the normal profile
of warm at the surface and
cooler as altitude increases is
‘inverted’ or turned upside down
Wikimedia Commons
Height (y-axis) versus Temperature (xaxis) under normal atmospheric
conditions (black line). The path D-C
illustrates an inversion aloft.
Cool air will be found at lower
altitudes, with warmer air above
during an inversion
Temperature Inversions and
Pollution
The normal movement and mixing of cold and warm air in our
atmosphere creates turbulence, which helps to lift and disperse
pollutants
Temperature inversions, however, keep cool, dense air near the
surface, reducing the vertical movement
Pollutants stay near the
surface
Pollutants become
concentrated as more are
added by everyday activities
Pollutant concentrations may
become hazardous
Favorable Conditions to Form a
Temperature Inversion
Calm winds ➯ reduce vertical mixing
Clear skies ➯ increase rate of surface
cooling
Less ‘greenhouse effect’
Rising smoke in Lochcarron, Scotland forms
a ceiling over the valley due to a temperature
inversion. The picture was taken on an
afternoon
in January after a cold night.
Wikimedia Commons
Other Favorable Conditions for Forming
a Temperature Inversion
Long nights ➯ greater duration of
cooling
Inversions more common in winter due to
longer
nights
Inversions are stronger in winter because of
the greater difference in temperature
between the cool surface air and the
warmer air aloft
A very low angle of the sun
in the sky (as in winter)
➯ less daytime heating of air
close to the ground and
surface
Wikimedia Commons
Types of Temperature
Inversions
Radiation Temperature
Inversion
Subsidence Temperature
Inversion
Shanghai
Wikimedia Commons
What Causes a Radiation
Temperature Inversion?
Cooling of the air at night near the
ground
Mechanism
1. Ground loses heat quickly after
sunset
2. Air in contact with ground then
cools quickly
3. Air above surface stays warm
since air is a poor conductor of
heat
Radiation Temperature
Inversions
Wikimedia Commons
Morning warming by the sun will often reverse a
temperature inversion by afternoon
Pollutants built up during the night also disperse
Radiation Temperature Inversions
and Topography
Areas in a mountain basin may experience prolonged
radiation temperature inversions
Cooler, denser air cannot rise up
over mountains to laterally
disperse pollutants
Mountains also block the low
angle of the winter sun, reducing
warming of the air
Cloudy weather will block the sun,
further decreasing warming
Mexico City
Wikimedia Commons
What Causes a Subsidence
Temperature Inversion?
A high altitude mass of warm air moves into an area
over cooler air near the surface
High pressure pushes the warm air mass down,
effectively capping the cooler air below
Fog may be seen under the
inversion cap
Subsidence temperature
inversions are usually shortlived
Fog over San Francisco
Wikimedia Commons
Subsidence Temperature
Inversions and Topography
Areas with mountains on three sides and the
ocean on the fourth may experience frequent
and prolonged subsidence temperature
inversions
Mechanism
1. Ocean breezes cool the surface air
2. Mountains surrounding prevent the cooler, heavier air from
dispersing over the mountains and removing pollutants
Subsidence Temperature
Inversions and Smog
These conditions are especially problematic in areas like Los Angeles, CA
Warm, sunny climate and high level of pollutants (vehicle, shipping, port)
causes a photochemical smog
Smog persists due to frequent subsidence temperature inversions for at
least half the year (summer and fall)
Low rainfall (15” per year) limits clearance of smog
David Iliff, http://en.wikipedia.org/wiki/File:Los_Angeles_Pollution.jpg
The Great London Smog of
1952
The Great Smog (AKA “Big
Smoke”) affected London in
1952
5 days in December
Temperature inversion
that caused the worst air
pollution event in UK
history
Nelson’s Column, London, during the Great Smog, December 1952
Wikimedia Commons
The Great Smog of 1952Meteorological Causes
Weather had been very cold, so more low-grade, high sulfur coal (the least
expensive) was being burned than usual
This increased sulfur dioxide in the air significantly
There was very little wind, thus little dispersal of pollutants
Cold, stagnant air was trapped under a layer of warmer air above
A high pressure area settled over London, decreasing air movement further (a
subsidence temperature inversion)
Prevailing winds blew heavily polluted air across the English Channel from
industrial areas of Europe
The Great Smog of 1952- Human
Causes
London had recently changed from
an electric tram system to diesel
buses; this diesel exhaust added
pollution and particulates to the
mix
Tarry particles of soot were also in
the mix from chimney smoke,
commercial, and industrial sources
Great Smog of 1952- Health
Impact
As Londoners were used to fog, there was no panic
initially
The very young and very old, however, began to have
respiratory problems, as did those who already had
chronic respiratory problems
Public transportation and even ambulances had to stop
running, as the
fog was so thick that
visibility was only a few
yards
Great Smog of 1952- Health
Impact
4,000 people died from respiratory tract
infections, lung infections, etc. during the
days of the smog
8,000 more people died from respiratory
problems in the months just after the Great
Smog
This episode made governments aware of
the need for legislation to clean up the air
to prevent a lethal situation in the future
Thermal Inversions in Georgia
Want to see a temperature inversion?
These sometimes happen in the
metro Atlanta area after a cold
fall or winter night when many
people have been using their
wood-burning fireplaces, or
have burned leaves during the
day
Try to view the area from a
higher vantage point to see the
full effect of the inversion
How to Help Limit Temperature Inversions
and Protect Yourself
When the conditions are conducive to forming an inversion, reduce activities
that might contribute, such as extra driving, burning wood, leaves, or refuse,
etc.
Wood smoke contains much more particulate pollution than oil- or gas-fired furnaces
Follow the Air Quality Index reports online, in the newspaper, or on radio and
follow recommendations for any change in activity
If you have respiratory problems, make a plan with
your care-givers as to what you need to do if
there is a thermal inversion with a lot of
pollution close to the ground
Practice the 3 Rs every day to limit overall pollution
from factories, power plants, transportation, and
waste disposal