Ionosphere
Ionosphere
| Topics: |  Ionosphere Space Science The Solar System |
The Upper Atmosphere
There is no true edge to the atmosphere, or a beginning to 'outer space'. The atmosphere just gets thinner and thinner. Even at altitudes of 10,000 kilometers - high above the orbit of the Space Station - there is still a lot of atmosphere left. The contact point or 'interface' between the magnetospheric system and the atmosphere reaches deeply into the atmosphere and ends at about the location of the ionosphere some 100 kilometers above the ground.
The ionosphere is an electrically-charged layer of gas that we use to reflect radio waves between distant stations. Energy and currents flow from the magnetosphere into the ionosphere, and back out into the magnetosphere, like an invisible electrical current. Along the way, some of these currents can cause the Northern and Southern Lights (Aurora Borealis and Aurora Australis) in the polar regions of Earth.
The location of the main ionospheric regions. (Courtesy University of Alaska/NASA.)
Meanwhile, lightning storms in the lower atmosphere cause electrical currents to flow into the upper atmosphere and ionosphere. The ionosphere receives energy both from the magnetosphere and from electrical storms in the lower atmosphere. This also means that the magnetospheric system can have some affect upon atmospheric electrical systems near the ground and in the lower atmosphere (troposphere). The sun also causes changes in the atmosphere above the ozone layer, as its ultraviolet light is absorbed and delivers energy to atoms there.
The Earth's atmosphere knows no true boundary. Even at the orbit of the Space Shuttle, there is still quite a lot of air there. Satellites can easily detect our atmosphere out to 10,000 kilometers from the Earth's surface. The outer atmosphere actually occupies the same region of space as the plasmasphere, the ring current and the van Allen Belts themselves. The Earth's atmosphere is far more complex than a simple onion-layered picture would suggest. These layers exchange gas and energy all the way out into the depths of the invisible magnetosphere, and deep into the atmosphere. One of the most interesting of these atmospheric layers is the ionosphere: A layer of charged particles surrounding the Earth at an altitude of about 100 kilometers. The ionosphere has been the workhorse of communication technology for most of the 20th century, until satellite communications offered another means of relaying radio messages from place to place across the globe. No sooner had Marconi invented the wireless radio in 1909, but scientists used this to prove that there must be a charged layer of gases several hundred miles above the Earth's surface. By 1931, it was also discovered that the charged layer could be upset by solar flares, causing radio blackouts across the globe. Just as a mirror reflects light, a cloud of charged particles can reflect longer-wavelength radio waves. The denser the cloud, the higher the frequency of the wave that can be reflected. In the ionosphere there are typically 100 charged particles per cubic inch, so this means that radio frequencies in the AM radio band are easily reflected, but it also means that the much higher frequency FM signals pass through it very easily. TV signals are at such high frequencies that the ionosphere is completely transparent. As a system, the ionosphere is electrically connected to the ground through the tops of thunder storm clouds, and it is connected to the rest of the magnetosphere through the magnetic lines of force and currents that flow along them.
The ionosphere is a lumpy, cloudy layer, and radio signals actually 'twinkle' like stars because of the changing transparency and location of these cloudlets, in a phenomenon called radio scintillation. Meteors that disintegrate near these layers also add their charged gases to this layer. Radio amateurs and the military alike use these meteor trails to reflect radio signals at very high frequencies; much higher than what the ionosphere can naturally reflect. Also in this layer, or near its base, we can occasionally see very high altitude clouds forming, which can be seen well after sunset. They are called noctilucent clouds and scientists still don't know how they form or why. Their appearance seems to have something to do with the level of solar activity.
External Links
- " 4D Ionosphere" a "4D" live model of Earth's ionosphere - Science@NASA.
- Basics of the Polar Ionosphere from the Real-Time UAF Eulerian Parallel Polar Ionosphere Model - Website: Arctic Region Supercomputing Center, University of Alaska.
- "First Global Connection Between Earth And Space Weather Found" - NASA, Goddard Space Flight Center. (Discusses Earth's ionosphere and weather interactions.)
- Images, Information and Maps from the Real-Time UAF Eulerian Parallel Polar Ionosphere Model - Website: Arctic Region Supercomputing Center, University of Alaska.
- "Index of Information About the Ionosphere" - High Frequency Active Auroral Research Program (HAARP).
- "The Ionosphere" - Space Physics and Aeronomy Section, American Geophysical Union.
- Space Physics and Aeronomy - University of Alaska.
Preview Image
This is a false-color image of ultraviolet light from two plasma bands in the ionosphere that encircle the Earth over the equator. Bright, blue-white areas are where the plasma is densest. Solid white lines outline the continents; Africa is on the left, and North and South America are on the right. Dotted white lines mark regions where rising tides of hot air indirectly create the bright, dense zones in the bands. The picture is a composite built up from 30 days of observations with NASA's IMAGE satellite (March 20 to April 20, 2002). (Source/Credit: NASA/University of California, Berkeley.)
Citation
Odenwald, Sten, Ph.D. (Contributing Author); Bernard Haisch (Topic Editor). 2008. "Ionosphere." In: Encyclopedia of the Cosmos. Eds. Bernard Haisch and Joakim F. Lindblom (Redwood City, CA: Digital Universe Foundation). [First published November 13, 2007].
<http://www.cosmosportal.org/articles/view/135813/>
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