Temperature Inversions - PowerPoint Presentation

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Temperature InversionsSlide2

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

NASASlide3

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.htmSlide4

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.htmSlide5

Air Temperature in the Lower Atmosphere

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 temperature in the troposphere therefore gets cooler as altitude increasesSlide6

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

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.

Wikimedia CommonsSlide7

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

Cool air will be found at lower altitudes, with warmer air above during an inversion

Height (y-axis) versus Temperature (x-axis) under normal atmospheric conditions (black line). The path D-C illustrates an inversion aloft.

Wikimedia CommonsSlide8

Temperature Inversions and PollutionThe 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 hazardousSlide9

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

Slide10

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 CommonsSlide11

Types of Temperature Inversions

Radiation

Temperature Inversion

Subsidence Temperature Inversion

Shanghai

Wikimedia CommonsSlide12

What Causes a

Radiation

Temperature Inversion?

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

Cooling of the air at night near the groundSlide13

Radiation Temperature Inversions

Morning warming by the sun will often reverse a temperature inversion by afternoon

Pollutants built up during the night also disperse

Wikimedia CommonsSlide14

Radiation Temperature Inversions and Topography

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

Areas in a mountain basin may experience prolonged radiation temperature inversionsSlide15

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 over San Francisco

Wikimedia Commons

Fog may be seen under the inversion cap

Subsidence temperature inversions are usually short-livedSlide16

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 pollutantsSlide17

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.jpgSlide18

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 CommonsSlide19

The Great Smog of 1952- Meteorological 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 EuropeSlide20

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 sourcesSlide21

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 yardsSlide22

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 futureSlide23

Thermal Inversions in Georgia

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

Want to see a temperature inversion?Slide24

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