Atmosphere Help (page 3)

Introduction to the Atmosphere

Do thoughts of space ships, hot air balloons, and kites come to mind when you think about the atmosphere? The atmosphere makes our world livable. It starts at ground level and then just goes on upward, getting thinner and colder until it finally dissolves into space. Without it, the Earth would be no more friendly than the Moon.

Many people think of the weather when they hear the word, atmosphere. Go to any party or meeting and pretty soon the weather topic comes up.

A meteorologist is a person who studies the weather and its atmospheric patterns.

It can be beautiful or dreary, hot or freezing, the weather (atmosphere) shapes our lives in a big way. Along the United States Gulf Coast, the common saying is, “if you don’t like the weather, then wait 10 minutes and it will change!” True of many places, the weather can change suddenly, especially around the time of seasonal shifts like spring and fall. Temperature drops of 30°F in two hours time are possible with a cold front.

What is our atmosphere made of? Air? Water? Smoke? You can’t even see the atmosphere except when there is fog, rain, snow, clouds, wind, or some other atmospheric filler.

Our current atmosphere is an oxidizing atmosphere, while the primordial atmosphere was a reducing atmosphere. That early atmosphere had little, if any, oxygen. It was more a product of volcanic emissions.

Today, there are several layers that make up our protective cover called the atmosphere , the lower layers have oxygen that we can breathe, while upper layers have much less.

Composition

The atmosphere we all know and love contains oxygen produced almost solely by algae and plants. It is made up of a mixture of roughly 79% nitrogen (by volume), 20% oxygen, 0.036% carbon dioxide, and trace amounts of other gases.

The atmosphere is divided into layers according to the mixing of gases and their chemical properties, as well as temperature. The layer nearest the Earth is the troposphere , which reaches an altitude of about 8km in the polar regions and up to 17km around the equator. The layer above the troposphere is the stratosphere , which reaches an altitude of around 50km. The mesosphere reaches up to 80–90km and lies above the stratosphere. Finally, the thermosphere , or ionosphere , is still further out and eventually fades to black in outer space. There is very slight mixing of gases between layers.

The atmosphere of the Earth exists as four distinct layers. Beginning with the closest layers to the ground, they include:

• Troposphere,
• Stratosphere,
• Mesosphere, and
• Thermosphere.

These four layers are illustrated in Fig. 14-1 . The location of the ozone layer is also shown.

Fig. 14-1. Four major layers make up the Earth’s atmosphere.

Troposphere

The lowest of the atmospheric layers, is the troposphere, extends from the Earth’s surface up to about 14 kilometers in altitude. Virtually all human activities occur in the troposphere. Mt. Everest, the tallest mountain on the planet, is only about 9km high.

Nitrogen and oxygen make up the majority of the Earth’s gases, even in the higher altitudes. But it’s the atmospheric layer closest to the Earth, where everything is just right to support life. At this level, living organisms are protected from the harmful cosmic radiation showers that constantly rain down on the Earth’s atmosphere.

This wonder layer is called the troposphere . If you have ever survived a hurricane or tornado, you know it’s an active place. The troposphere is the atmospheric layer where all the weather we experience takes place. Rising and falling temperatures, as well as circulating air masses keep things lively. Air pressure also adds to the mix.

When measured next to the other layers, the troposphere is fairly thin, reaching roughly 17km up from the Earth’s surface.

The troposphere is where all the local temperature, pressure, wind, and precipitation changes take place.

The warmest portions of the troposphere are found at the lowest altitudes. This is because the earth’s surface absorbs the Sun’s heat and radiates it back into the atmosphere. Commonly, as altitude increases, temperature decreases.

However, there are some exceptions. Depending on wind currents, mountain ranges can cause lower troposphere areas to have an opposite effect. Temperatures actually increase with altitude. This is called a temperature inversion . Generally, the temperatures at the top of the troposphere have lows of around –57°C. The wind speeds rise, causing the upper troposphere limits to be cold and windy. The air pressure at the top of the troposphere is only 10% of that at sea level. A mixer zone between the troposphere and stratosphere is called the tropopause .

Stratosphere

There is a gradual change from the troposphere to the stratosphere , which starts at around 11km in altitude. Here, the air flows mostly sideways. The stratosphere extends from 10km to around 50km. Most commercial aircraft travel takes place in the lower part of the stratosphere.

Although the temperature in the lower stratosphere is cold and constant, hovering around at –57°C, there are strong winds in this layer that occur as part of specific circulation patterns. However, extremely high and wispy clouds can form in the lower stratosphere. In general, there are no major weather formations that take place regularly in the stratosphere.

The stratosphere has an interesting feature from mid-level on up. Its temperature jumps up suddenly with an increase in altitude. Instead of a frosty –57°C, the temperature jumps up to a warm 1°C around 40km in altitude in the upper stratosphere. This temperature change is due to increasing ozone concentrations which absorbs ultraviolet radiation.

The merging of the stratosphere upward into the mesosphere is called the stratopause .

Ozone

Since even small amounts have a significant role in protecting the life on the planet, ozone levels are important. Concentrated in a thin layer in the upper stratosphere, ozone is an exceptionally reactive form of oxygen. Atmospheric ozone is found in a layer in the stratosphere, around 15–30km above the Earth’s surface. This ozone layer is largely responsible for absorbing most of the sun’s ultraviolet (UV) radiation. Most importantly, it absorbs the fraction of ultraviolet light called UVB .

Ultraviolet radiation is a bad, bad thing! It causes breaks in the body’s nuclear proteins leaving the door open for cancers and other health issues to take place. UVB has been connected with many serious health effects, like different kinds of skin cancer and cataracts. It is also harmful to certain crops, materials, and marine organisms.

Ozone is much less widespread than normal oxygen. The formation of the ozone layer is a tricky matter. Out of every 10 million air molecules, about 2 million are normal oxygen, but only 3 are ozone molecules. Instead of two atoms of oxygen like normal oxygen molecules (O ₂ ), ozone (O ₃ ) contains three oxygen atoms. Ozone has a distinctive odor and is blue in color. Regular oxygen has no odor or color.

Only through the production of atmospheric oxygen can ozone form to block the intense effects of ultraviolet radiation from reaching the surface and the plants and animals living there. In the past 30 years, there has been intense concern over decreased ozone levels. This is a big problem if we want to go on enjoying the out-of-doors and growing food in the centuries to come!

The annual “hole” or thinning of the ozone layer over Antarctica was first noticed in the spring times of the early 1980s. This area of extremely low ozone levels was having drops of over 60% during bad years. Additionally, research found that ozone depletion also took place over the latitudes of North America, Europe, Asia, Australia, South America, and much of Africa. It became obvious that ozone decreases were a global concern.

Atmospheric scientists have studied and recorded these annual and geographical fluctuations for years. There are usually cyclic downturns in ozone levels, followed by a recovery. However, as our population increases along with industrialization, global atmospheric changes are taking place as well.