Saturday, April 2, 2011

The five layers of the Atmosphere

Troposphere



The troposphere is the layer closest to the earth, and it is the layer in which
we live. It is about ten miles deep. Seventy five percent of the mass of all
our atmospheric molecules is in the troposphere, and this is where we find
water vapor, dust, pollen, and soot particles. Weather happens in the
troposphere. This layer is turbulent, with storms and atmospheric mixing.
In the troposphere, the air cools gradually as it gets further from the earth.
At the very top of this layer the air temperature is about 76 degrees below
zero on the Fahrenheit scale. This is important, because it changes water
vapor into ice, forming the cold trap, a temperature region where water
vapor stops going up. If we had no cold trap, water molecules could rise in
the atmosphere where they would eventually break down into oxygen and
hydrogen. The small, light hydrogen molecules could then escape into space.
Earth would loose its water if we had no cold trap








Stratosphere(can include the ozone layer)



The stratosphere lies above the troposphere. It is about twenty miles
deep. The stratosphere contains about 24% of the mass of all the
atmospheric molecules. This layer has the ozone layer in it. The
ozone layer protects all life on earth from the harmful and potentially
even lethal ultraviolet radiation emitted by the sun. There is not very
much ozone -- if it were all together, it would form a layer only three
millimeters thick. Three millimeters is not quite this deep: __ .
The lower part of the stratosphere is cold, but it warms up as it
gets farther from the earth -- another effect of the ozone. This layer is
peaceful compared to the troposphere. If you have been watching the
math, you see that
• The troposphere is 10 miles deep and has 75% of the mass of the atmosphere • The stratosphere is 20 miles deep and has 24% of the mass of the atmosphere This means that the lowest 30 miles of the atmosphere has 99% of
the mass of the molecules! However, the atmosphere goes out to
40,000 miles. It makes sense, then, that the atmospheric molecules
get farther and farther apart from each other as they go up the
remaining 39,970 miles, and that is just what they do. Although there
are some atmospheric molecules up here, they are scattered and
occasional, not like our thick ocean of air close to the surface.
The entire atmosphere of the earth extends out about 40,000
miles above the earth -- and the earth is about 8000 miles across.
The moon is a little less than 240,000 miles away.








Mesosphere
The mesosphere, which means middle sphere, is the third layer of Earth's atmosphere, between the stratosphere, and the thermosphere. It is located from about 55 kilometers (35 miles) to 85 kilometers (54 miles) above the surface of Earth. Temperature here decreases with height, so within the mesosphere it is warmest at its lowest level (−5°C, or 23°F), and becomes coldest at its highest level (−80°C, or −112°F). Depending on latitude and season, temperatures in the upper mesosphere can be as low as −140°C (−220°F). The temperature in the mesosphere is lower than the temperature of the troposphere or stratosphere, which makes the mesosphere the coldest among the atmospheric layers. It is colder then Antarctica's lowest recorded temperature, and it is cold enough to freeze water vapor into ice clouds, which can be seen mostly after sunset.




Thermosphere and Exosphere

The thermosphere and the exosphere are the outermost shells of the Earth’s atmosphere, in which artificial satellites and other spacecrafts follow orbits. The analysis of the variations in the orbits of artificial satellites has incidentally made a first important contribution to the study of the physic structure of this atmospheric layer.
An in-depth knowledge of the atmosphere’s outermost part, that is to say of the thermosphere and the exosphere, is in itself important as fundamental research and is a part of a global study of the Earth’s environment.
That knowledge has also resulted indispensable to determine the aerodynamic characteristics of spacecrafts, to assess the duration during which spacecrafts can be active in an orbit around Earth, and to select the most appropriate satellite orbits for research and for applications in the field of geodesy, navigation, teledetection, and meteorology.
When scientists, for instance, want to make long-term observations of Earth with high resolution, they chose a circular orbit that is not prone to all the possible disturbances which considerably alter the orbit, causing the satellites to return too soon.
In addition, the outermost part of the atmosphere is the natural environment for astronauts and cosmonauts, when they conduct a spacewalk to construct or repair space stations and to fetch or mend satellites.