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ISTP News May 2000
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Aurora Over the North Pole of Earth
NASA's Polar spacecraft took these two images of the aurora over Earth's northern hemisphere. The images were collected by Polar's Visible Imaging System in February 2000, and they reveal the auroral oval around the polar regions in visible and ultraviolet light. The most intense auroral activity -- typically provoked by magnetic reconnection events in Earth's tail -- appears in bright red or white. See animation
Credit: University of Iowa/NASA Scientific Visualization Studio
Correlation of Reconnection with Auroras
Scientific data from the Polar and Geotail spacecraft show how changes in the magnetic field and speed of plasma in Earth's tail (bottom half) precedes the brightening of the auroral oval (known as a substorm) by a matter of minutes. Scientists interpret this to mean that as reconnection happens in Earth's magnetic tail, energy flows down to Earth as the aurora.
Credit: Akimasa Ieda/NASA
Schematic Diagram of Aurora-Reconnection Correlation
This cartoon shows how Geotail measured the flow of plasma away from Earth -- "plasmoids" sliding down the tail after reconnection -- and Polar measured the arrival of plasma and energy flowing in the other direction, toward Earth.
Credit: Akimasa Ieda/NASA
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Global View of Magnetic Reconnection
These still frames come from an animation depicting how the magnetic field of the Sun -- carried by the solar wind -- can be deflected by or attached to Earth's magnetosphere (yellow lines).
1) When the solar wind is oriented with a southward magnetic field, it connects to the Earth's northward field (making orange field lines). 2) This magnetic reconnection pulls field lines (in orange) from the day side of Earth around to the night side, and allows electrified gas (plasma) to pour into the tail of the magnetosphere. 3) As the field lines pile up on the night side, the system becomes unstable. 4) Reconnection happens again -- this time in the middle of the tail. Particles and energy are shot down toward Earth's poles to make auroras, while a blob of plasma pinches off of the tail and flows downwind of Earth.
Credit: Angela Cheyunski/Honeywell Max-Q Digital Group for NASA
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Shaping Earth's Magnetosphere These two images are still frames from an animation depicting how Earth's magnetosphere is stretched from a simple, symmetrical dipole field into a windsock- or jellyfish-shaped body.
1) Like a bar magnet, Earth has a dipole magnetic field -- that is, a north and south magnetic pole. If there were no solar wind, Earth's magnetosphere would make a near-perfect dipole. But as we see in the second image (2), when the magnetized solar wind blows past the Earth, it compresses the day (or sunlit) side of Earth's field and stretches out the night side into a long tail.
Credit: Angela Cheyunski/Honeywell Max-Q Digital Group for NASA
Artist's Conception of the Solar Wind-Magnetosphere Interaction,
from the Space Weather Center museum exhibit
Credit: Steele Hill/NASA
Title: Artist's Conception of the Sun-Earth System,
from the "Electric Space" museum exhibit
Credit: Steve Mercer/Space Science Institute

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