11 December 2007

Giant Magnetic Ropes and Magnetic Explosions! THEMIS Looks At the Sun-Earth Magnetic Connection

A set of 5 satellites under NASA's "Time History of Events and Macroscale Interactions during Substorms (THEMIS)" mission are beginning to accumulate evidence of "magnetic ropes" connecting the sun to Earth's upper atmosphere:
"The satellites have found evidence of magnetic ropes connecting Earth's upper atmosphere directly to the sun," said David Sibeck, project scientist for the mission at NASA's Goddard Space Flight Center in Greenbelt, Md. "We believe that solar wind particles flow in along these ropes, providing energy for geomagnetic storms and auroras."

A magnetic rope is a twisted bundle of magnetic fields organized much like the twisted hemp of a rope. Spacecraft have detected hints of these ropes before, but a single spacecraft was insufficient to map their 3-D structure. THEMIS' five identical micro-satellites were able to perform the feat.

"THEMIS encountered its first magnetic rope on May 20," said Sibeck. "It was very large, about as wide as Earth, and located approximately 40,000 miles (70,000 kilometers) above Earth's surface in a region called the magnetopause." The magnetopause is where the solar wind and Earth's magnetic field meet and push against one another like sumo wrestlers locked in combat. There, the rope formed and unraveled in just a few minutes, providing a brief but significant conduit for solar wind energy....Sometimes a burst of electrical current within the solar wind will hit the bow shock and -bang! We get an explosion."

One such explosion occurred on July 4, releasing as much energy as 100 million firecrackers (10 gigajoules), according to UC Berkeley research physicist Jonathan Eastwood. These so-called "hot flow anomalies" occur when a discontinuity in the solar magnetic field - evidenced by an electrical current - hits the bowshock and decelerates from a million miles per hour to a dead stop. The area of plasma heats rapidly by a factor of 10 to as much as 10 million degrees Celsius...

Clearly there are tremendous electromagnetic energy transfers between Sol and the Earth. How does this fascinating electromagnetic connection tie in to Earth's variable climate? If we keep studying the profound everyday influence of our star with our planet, we just may find out.

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