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Instruction 5-3
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Circulation Patterns in the Earth's Atmosphere and Oceans | The Relationship Between the Rotation of the Earth and the Circular Motion of Ocean Currents and Air in Pressure Centers | The Origin and Effects of Temperature Inversion | Properties of Ocean Water | Location of Deserts and Rain Forests | Features of ENSO

The Origin and Effects of Temperature Inversion
CCSTD Earth Science 5.c.

A temperature inversion is a condition in which the temperature of the atmosphere increases with altitude.

This is the exact opposite of (or inversion of) the normal situation in which temperature decreases with altitude, at least in most parts of the atmosphere.

This can result in cooler air at the surface being trapped by warmer air above it.

There are a number of reasons why this can happen. And there can be serious consequences, like mirages and smog.

But to understand temperature inversion we need to review the composition of the atmosphere under normal (non-inversion) conditions.

Our Layered Atmosphere

The Earth's atmosphere is made up of four different layers.

The Troposphere

The layer of the atmosphere nearest the Earth is called the troposphere. It is between 8 to 16 km deep. It is deeper at the Equator and thins out toward the poles, which makes its average depth about 11 kilometers.

The troposphere contains about 80% of the total mass of the atmosphere, and it is where most of our weather occurs.

The temperature in the troposphere decreases with altitude at a rate of approximately 6.5 degrees Celsius per 1000 meters.

At the top of the troposphere is a narrow transition zone called the tropopause.

The Stratosphere

The layer above the tropopause is called the stratosphere. This layer extends from 11 to 50 km above the Earth's surface.

The stratosphere contains about 19% of the atmosphere's total mass, and very little weather occurs here (except for the top of an occasional thunderstorm).

In the first 9 kilometers of the stratosphere, temperature remains constant with height. But from 20 to 50 kilometers, temperature in the stratosphere increases with altitude.

This unusual situation occurs because of a heavy concentration of ozone gas molecules. These molecules absorb ultraviolet sunlight and warm this part of the stratosphere.

This is called the ozone layer. It is important to organisms on Earth since it
protects them from the harmful effects of the Sun's ultraviolet radiation. Life couldn't exist without it.

At the top of the stratosphere is another transition zone called the stratopause.

The Mesosphere

The next layer of the atmosphere is called the mesosphere. It extends from 50 to 80 kilometers.

The temperature in the mesosphere decreases with altitude -- and can fall as low at -90 degrees Celsius (the coldest temperature in the atmosphere). At the top of the mesosphere is a transition zone called the mesopause.

The Thermosphere

The last layer of the atmosphere, the thermosphere, begins at about 80 km.

This is the hottest layer in the atmosphere, where temperatures actually increase with altitude.

It's so hot because its oxygen molecules absorb solar radiation -- and temperatures can rise to 1800 degrees Celsius.

The upper part of the thermosphere is called the Ionosphere.

Here, enough free electrons exist to have a major effect on radio frequency electromagnetic waves (reflecting them back to Earth). The degree to which this occurs depends on the activity of the Sun (seasons, sunspots and so on).

Temperature Inversion

As we said, air normally cools as its rises. This is due to convection, a process of heat transfer in which air near the surface of the Earth is heated by the Sun, expands and rises -- only to be replaced by cooler air which begins the process all over again.

But sometimes this process can be inverted (turned upside down) and air actually gets colder nearer the Earth's surface.

This is usually caused by air masses with different temperatures moving over one another, shutting down the convection process.

A warm air mass moving over a colder one can keep the cooler air mass trapped below.

This means that air can no longer circulate, surface air can no longer rise, and air pollution is trapped at the surface. The result is haze, a general "stillness" of the air and smog.

A strange optical effect can also occur, in which distant objects appear to
be stretched out or floating above the horizon. This is called a mirage or Fata Morgana (after Morgana, King Arthur's shape-shifting half sister).

Radio and TV reception from distant stations is also common during a temperature inversion.

The only cure for a temperature inversion is a strong horizontal wind. But since high-pressure systems often combine temperature inversions with low wind speeds, severe long-lasting effects in certain areas (like Los Angeles) can often occur.

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Now let's do Practice Exercise 5-3 (top).

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