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Northern Lights: Earth Activity

The unique structure of Earth's atmsophere and magnetic field play a critical role in protecting us from deadly radiation and space weather. Their specific characteristics determine why, how, when, and where the Northern Lights occur, so it is very important to spend some time learning about how they work.

  • Atmosphere
  • Magnetosphere
  • Van Allen Belts
  • Aurora

Atmosphere Layers

Earth's atmosphere gradually dissipates into space, but we define separate layers based on characteristics at each altitude, particularly how temperature changes with height. Scroll down to get a complete view of the Earth's atmosphere. Wikipedia does a great job describing the different layers.

More LayersThe thermosphere and some of the exosphere are part of the "ionosphere". The Ionosphere is the layer of charged particles that have been ionized by solar radiation, knocking off some of their electrons. These charged particles interact strongly with plasma from the Sun, and are responsible for most the space weather we experience. The ionosphere marks the inner edge of the Magnetosphere, but this boundary varies depending on the strength of geomagnetic storms.

You can see that even satellites such as the Hubble Space Telescope that orbit Earth are still partially in the atmosphere. Even the Space Shuttle orbits only a couple hundred of miles up.

The Northern Lights occur in the thermosphere below the International Space Station's (ISS's) orbit. This means that astronauts are above the safe zone and are exposed to much of the dangerous high energy radiation that accompanies geomagnetic storms. They also get a good view of the lights.

Knowledge of the atmosphere may also be useful for your remote sensing project. Your blimp is tethered so that it will not rise much more than 150 feet, so it will stay in the troposhere. At this level, the temperature of the air decreases with height. This is called the "Lapse Rate", and it amounts to about 7 degrees Celsius per kilometer.

Altitude vs. Temperature and PressureYou can see how the temperature and pressure in the atmosphere change with altitude in the graphs at right. These graphs were made with data taken by a high altitude balloon in Great Falls, MT.

At low altitudes, such as those in the troposphere, we get the highest temperatures and pressures. Temperature steadily decreases with altitude at the "Lapse Rate" until about 13km, where it starts to increase again, zig-zagging back and forth. Pressure steadily decreases with altitude and quickly dissipates above the 30km mark.




Earth's Magnetic FieldEarth's Magnetic Field:

If you have used a compass before, you are probably familiar with the fact that Earth has a magnetic field. Earth’s magnetic field is very similar to a huge bar magnet. While it has some complicated twists and loops inside the Earth (as shown below at right), the general structure loops out of the earth near Antarctica and into the earth in the arctic islands of Northern Canada, wrapping around outside. The north pole of a compass points to the Earth's geographic North pole, which is physically a magnetic South pole. We call it the Magnetic North Pole because it is where the North pole of a compass points. And even the place where compasses point is slightly skewed from the geographic north pole (as seen below (image used with permission of Peter Reid( Earth's Magnetic FieldReal Field Lines









Earth's Magnetosphere


The magnetic field lines of the earth extend into outer space far beyond our atmosphere. The protective case this creates around earth is called the Magnetosphere. Earth’s magnetosphere isn’t quite spherical -  its shape is modified by the solar wind and the interplanetary magnetic field, which give it an oblong shape that points away from the Sun.

The magnetosphere protects us from the dangerous high-energy particles from the solar wind and other space weather by deflecting most of the high energy particles from the Sun around earth.

Van Allen Radiation BeltsAt a distance of about one and half Earths away lies the Van Allen Radiation Belts. The two belts (inner and outer) are torus shapes - hollow lobes that surround the Earth. Each belt is composed of energetic free electrons and some protons. Though above most satellite and space shuttle orbits, the charged particles move fast enough to create dangerous radiation to astronauts that may pass through. The belts are not well-understood, but they are believed to play a part in auroral activilty by streaming charged particles back and forth between the Earth's North and South magnetic poles.

Auroral Oval

Aurora occur when an influx of charged particles from the Sun get trapped by the Earth's magnetic field and strung along the field lines to the poles. At the North pole they are called the Aurora Borealis, or the Northern Lights, and at the South pole they are called the Aurora Australis, or the Southern Lights. The Earth's magnetic field lines protude in a ring pattern at each pole. However, the solar wind pushes against the magnetosphere, causing the circle to bulge into more of an oval, pointing away from the Sun. As the solar particles encounter the atmosphere, they energize oxygen and nitrogen atoms, creating an "auroral oval" of beautiful colors.

As the particles stream in, the colors appear to ripple with a curtain-like appearance. You can watch an amazing timelapse video of the this effect here.

Aurora from aboveAurora from space








Astronauts in space get an amazing view that showcases how high in the atmosphere the aurorae occur, as shown by the images above. On the ground, however, we only view a small portion of the auroral oval, and it is difficult for us to discern a definite shape or to tell from how high the colors are arriving. From the ground, the aurorae may appear just as a faint change in color of the sky, but occasionally the most spectacular views show the rippling curtain effect. Faint AuroraAurora over Alaska