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The Ionosphere Explained: What does the ionosphere have to do with the aurora?
What
is the ionosphere?
The ionosphere is a name for
the layer of the earth's atmosphere that is ionized by solar radiation.
The more common name for this radiation is solar wind. Even though
many believe the space around earth is a vacuum, it is not completely
empty. The sun's upper atmosphere (the corona) is very hot and some
of its hydrogen and helium are able escape the sun's gravity. Because
the gas is hot and is in a constant stream of solar energy it becomes
a fully ionized plasma.
This streaming plasma is the solar wind, and it flows out past the
earth affecting the earth's magnetic field, the magnetosphere and
ionosphere. The Earth receives a lot of energy from the sun in the
form of radiation- about 1370 Watts per square meter! That is enough
energy to power 6 desktop computers coming from an area you
could barely fit one computer into! Who
Discovered the Ionosphere? The discovery of
the ionosphere came together through the work of many people from
different fields. In 1864 James Clerk Maxwell proposed a theory
of how electromagnetic waves could be created by using an oscillating
magnetic and electric field together. He realized that light is
an eletromagnetic wave and just a very small visible part of the
electromagnetic spectrum that could be used for other things. In
1901 Marconi used Maxwell's discovery to send radio waves (electromagnetic
waves of a lower frequency than light) across the Atlantic Ocean.
He realized that because the listening station was out of his line
of sight, the electromagnetic waves he was sending must be bouncing
off some part of the atmosphere and travelling back further than
expected. In 1902 Oliver Heaviside and Arthur Kennelly heard of
Marconi's interesting discovery and proposed that there was a conducting
reflective layer that was bouncing these waves back to earth, the
Ionosphere! What
is the structure of the ionosphere? F-region: 150-1000km
contains a range of ion from NO+ and O+ at the bottom to H+ and
He+ ions at the top. Electron density is highest in this layer. E-region: 95-150km,
contains mostly 02+ ions D-region: 75-95
kilometers up, relatively weak ionization due to its position at
the bottom. Click here
for a diagram showing electron concentration and temperature vs.
altitude. Why
is the Ionosphere important? Our society has
learned to use the properties of the ionosphere in many beneficial
ways over the last century (radio, television, satellite communications,
etc.), but there is still a great deal to learn about its physics,
its chemical makeup and its everyday changes because of solar radiation.
The upper parts
of the ionosphere can be studied to some extent with satellites
but the lower levels are below orbital altitudes while still too
high to be studied using instruments carried by balloons or high
flying aircraft. Most of what we know now is from ground-based observations
of: Some very useful
information has been obtained using rockets (for example, from the
Poker Flat Research Range
near Fairbanks, AK). What
does the ionosphere have to do with the aurora? Above the north
and south poles there is an oval region in which there is no magnetoshpere,
charged particles can enter the ionosphere and excite its weaker
neutral plasma. These particles excite the electrons in the neutral
gas, which in turn radiate the energy as visible light at frequencies
which are characteristic of the particular gas which was excited,
just like flourescent lighting: "In a florescent light tube,
the inside is a near vacuum," explains Patrick Newell in an
article in Nature. "An electric field (the voltage from your
wall socket) is applied across the ends. The electric field accelerates
electrons, that then strike the small amount of gas inside, giving
off light." This all happens in the ionosphere, 60-200km up. For more information
on the aurora, try Neal Brown's Alaska
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The
ionosphere is composed of three main parts: the D, E, and F regions.
