Atmosphere Help

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.

Mesosphere

Above the stratosphere is the mesosphere , a middle layer separating the lower stratosphere from the inhospitable thermosphere. Extending from 80 to 90km and with temperatures to around –101°C, the mesosphere is the intermediary of the Earth’s atmosphere layers.

Military aircraft travel at much higher altitudes, with some classified, stealth aircraft thought to graze the boundary of the mesosphere and beyond.

Thermosphere

The changeover from the mesosphere to the thermosphere layer begins at a height of approximately 80km. The thermosphere is named because of the return to rising temperatures that can reach an amazing 1982°C. The different temperature ranges in the thermosphere are affected by high or low sun spot and solar flare activity. The more active the sun is, the higher the heat generated in the thermosphere.

Extreme thermosphere temperatures are a result of UV radiation absorption. This radiation enters the upper atmosphere, grabbing atoms from electrons and creating positively charged ions. Electrically charged atoms build up to form layers within the thermosphere. This ionization causes the thermosphere to also be called the ionosphere . Because of ionization, the lowest area of the thermosphere absorbs radio waves, while other areas reflect radio waves. Since this area decreases and disappears at night, radio waves bounce off the thermosphere. This is why far distant radio waves can often be received at night. Today, radio frequencies that can pass through the ionosphere unchanged are selected for satellite communication.

The aurora is found in the thermosphere. The Aurora Borealis and Aurora Australis , the northern and southern lights, are found in the thermosphere. When solar flares slam the magnetosphere and pull electrons from their atoms, they cause magnetic storms near the poles. Look back to Fig. 1-9 to review the magnetic currents that encircle the Earth.

Dazzling red and green lights are created when scattered electrons reunite with atoms, returning them to their original state. Even higher, above the auroras and the ionosphere, the gases of this final atmospheric layer begin to scatter. Several hundred kilometers above the earth, they fade into the fabric of space. NASA’s Space Shuttle generally travels to altitudes between 160 and 500km above the Earth.

Practice problems of this concept can be found at: Atmosphere Practice Test