Layers of the Earth's Atmosphere (Part 2)

The Troposphere

The troposphere is the lowest layer of the Earth's atmosphere. The air is very well mixed and the temperature decreases with altitude.
Air in the troposphere is heated from the ground up. The surface of the Earth absorbs energy and heats up faster than the air does. The heat is spread through the troposphere because the air is slightly unstable.
Weather occurs in the Earth's troposphere.

The Stratosphere

In the Earth's stratosphere, the temperature increases with altitude. On Earth, ozone causes the increasing temperature in the stratosphere. Ozone is concentrated around an altitude of 25 kilometers. The ozone molecules absorb dangerous kinds of sunlight, which heats the air around them.
The stratosphere is located above the top of the the troposphere.

Ozone - An Overview

The Ozone Hole. Pollution. Skin Cancer. Why does the topic of ozone make the news so much? How important is the ozone in our atmosphere? Why are scientists so concerned about its increase near the surface of the Earth and its disappearance higher up in the atmosphere?
First things first - what is ozone? Ozone is made of three oxygen atoms (O3). The oxygen in our atmosphere that we breathe is made up of two oxygen atoms (O2). When enough ozone molecules are present, it forms a pale blue gas. Ozone has the same chemical structure whether it is found in the stratosphere or the troposphere. Where we find ozone in the atmosphere determines whether we consider it to be "good" or "bad"!
In the troposphere, the ground-level or "bad" ozone is an air pollutant that damages human health, vegetation, and many common materials. It is a key ingredient of urban smog. In the stratosphere, we find the "good" ozone that protects life on Earth from the harmful effects of the Sun's ultraviolet rays. We have good reason to be concerned about the thinning of the ozone layer in the stratosphere. We also have good reason to be concerned about the buildup of ozone in the troposphere. Although simplistic, the saying "Good up high and bad near by," sums up ozone in the atmosphere.

Ozone in the Stratosphere

About 90% of the ozone in the Earth's atmosphere is found in the region called the stratosphere. This is the atmospheric layer between 16 and 48 kilometers (10 and 30 miles) above the Earth's surface. Ozone forms a kind of layer in the stratosphere, where it is more concentrated than anywhere else.
Ozone and oxygen molecules in the stratosphere absorb ultraviolet light from the Sun, providing a shield that prevents this radiation from passing to the Earth's surface. While both oxygen and ozone together absorb 95 to 99.9% of the Sun's ultraviolet radiation, only ozone effectively absorbs the most energetic ultraviolet light, known as UV-C and UV-B. This ultraviolet light can cause biological damage like skin cancer, tissue damage to eyes and plant tissue damage. The protective role of the ozone layer in the upper atmosphere is so vital that scientists believe life on land probably would not have evolved - and could not exist today - without it.
The ozone layer would be quite good at its job of protecting Earth from too much ultraviolet radiation - that is, it would if humans did not contribute to the process. It's now known that ozone is destroyed in the stratosphere and that some human-released chemicals such as CFC’s are speeding up the breakdown of ozone, so that there are "holes" now in our protective shield.
While the stratospheric ozone issue is a serious one, in many ways it can be thought of as an environmental success story. Scientists detected the developing problem, and collected the evidence that convinced governments around the world to take action. Although the elimination of ozone-depleting chemicals from the atmosphere will take decades yet, we have made a strong and positive beginning. For the first time in our species' history, we have tackled a global environmental issue on a global scale.

The Mesosphere

In the Earth's mesosphere, the air is relatively mixed together and the temperature decreases with altitude. The atmosphere reaches its coldest temperature of around -90°C in the mesosphere. This is also the layer in which a lot of meteors burn up while entering the Earth's atmosphere.
The mesosphere is on top of the stratosphere The upper parts of the atmosphere, such as the mesosphere, can sometimes be seen by looking at the very edge of a planet.

The Thermosphere

The thermosphere is the fourth layer of the Earth's atmosphere and is located above the mesosphere. The air is really thin in the thermosphere. A small change in energy can cause a large change in temperature. That's why the temperature is very sensitive to solar activity. When the sun is active, the thermosphere can heat up to 1,500° C or higher!
The Earth's thermosphere also includes the region of the atmosphere called the ionosphere. The ionosphere is a region of the atmosphere that is filled with charged particles. The high temperatures in the thermosphere can cause molecules to ionize. This is why an ionosphere and thermosphere can overlap.

The Ionosphere

Scientists call the ionosphere an extension of the thermosphere. So technically, the ionosphere is not another atmospheric layer. The ionosphere represents less than 0.1% of the total mass of the Earth's atmosphere. Even though it is such a small part, it is extremely important!
The upper atmosphere is ionized by solar radiation. That means the Sun's energy is so strong at this level, that it breaks apart molecules. So there ends up being electrons floating around and molecules which have lost or gained electrons. When the Sun is active, more and more ionization happens!
Different regions of the ionosphere make long distance radio communication possible by reflecting the radio waves back to Earth. It is also home to auroras.
Temperatures in the ionosphere just keep getting hotter as you go up!

Regions of the Ionosphere

The ionosphere is broken down into the D, E and F regions. The breakdown is based on what wavelength of solar radiation is absorbed in that region most frequently.
The D region is the lowest in altitude, though it absorbs the most energetic radiation, hard x-rays. The D region doesn't have a definite starting and stopping point, but includes the ionization that occurs below about 90km.
The E region peaks at about 105km. It absorbs soft x-rays.
The F region starts around 105km and has a maximum around 600km. It is the highest of all of the regions. Extreme ultra-violet radiation (EUV) is absorbed there.
On a more practical note, the D and E regions reflect AM radio waves back to Earth. Radio waves with shorter lengths are reflected by the F region. Visible light, television and FM wavelengths are all too short to be reflected by the ionosphere. So your t.v. stations are made possible by satellite transmissions.

The Sun's Effect on the Ionosphere

Invisible layers of ions and electrons are found in the Earth's atmosphere. We call this region of atmosphere the ionosphere.
The main source of these layers is the Sun's ultraviolet light which ionizes atoms and molecules in the Earth's upper atmosphere. During this process, electrons are knocked free from molecules or particles in the atmosphere.
Flares and other big events on the Sun produce increased ultraviolet, x-ray and gamma-ray photons that arrive at the Earth just 8 minutes later (other particles from the Sun may arrive days later) and dramatically increase the ionization that happens in the atmosphere. So, the more active the Sun, the thicker the ionosphere!

The Exosphere

Very high up, the Earth's atmosphere becomes very thin. The region where atoms and molecules escape into space is referred to as the exosphere. The exosphere is on top of the thermosphere.
 Dwi A(08_44)