University of Iowa physics professor Jack Scudder said today (Thursday, June 1) that an international team of physicists has significantly advanced mankind's understanding of the northern lights and related phenomena by making the first direct observations of the switch that permits energy to be transferred between the solar wind and the Earth.
Scudder, who spoke on behalf of his co-authors at a news conference at the spring meeting of the American Geophysical Union in Washington, D.C., noted that the naturally occurring switch for this energy transfer, known as "magnetic reconnection," is responsible for the aurora borealis and australis, as well as occasional interruptions in radio and satellite communications. He said that the outer layer of the Earth's magnetosphere generally behaves like a cocoon, shielding the Earth from reconnection, but that every once in a while a tear appears as a result of reconnection.
"Sometimes the solar wind creates tears in the cocoon, and charged particles and energy from the sun penetrate into the magnetosphere," said Scudder, who is principal investigator for the Hot Plasma Analyzer (HYDRA) on NASA's Polar spacecraft. "We have directly observed these tears for the first time using Polar.
"One of the most exciting things about the detection is finding that such small-scale structures really do exist in the precise sizes predicted 25 years ago. Some of these tears are extremely small -- on the order of one kilometer long," he said.
In the current investigation, scientists involved in the multi-satellite International Solar-Terrestrial Physics (ISTP) program identified two general areas where reconnection occurs. One region penetrated by Polar is 30,000 to 40,000 miles on the dayside of the cocoon, and the other (observed by the Geotail satellite) is inferred to be some 85,000 to 96,000 miles downwind of the Earth, on the night side of the planet and in the tail of the teardrop-shaped magnetosphere. ISTP is a collaborative study between NASA, the Japanese space agency (ISAS), and the European Space Agency (ESA), with contributions from Russia's Institute for Space Research (IKI) and many other international science institutions.
The observation of magnetic reconnection is of interest to physicists because it answers a half-century-old question surrounding the origin of the energy responsible for auroras and magnetic disturbances. On the dayside of the Earth, reconnection allows energy from the solar wind to enter the magnetosphere, that volume of magnetic fields surrounding the Earth that contains the Van Allen radiation belts. On the night side, reconnection permits the transfer of energy down to the Earth's atmosphere, but the whole sequence is started by reconnection on the dayside, as observed by Polar.
"Everything that happens regarding space weather happens through and because of these slits," Scudder said. "We're excited that the data clearly show the electrons jumping through these slits, doorways really, that open the Earth to these particles from space. The $64 question is what makes the tears possible. We'd like to see some more of them to know whether those already detected represent a general or an unusual picture of the switch."
To better define where the tears take place, Scudder has helped outline an entire NASA satellite mission. Dubbed BLAST (Boundary LAyer SnapshoT), it would carefully study these small, but crucial, intersections of the magnetic highways between the sun and the Earth. The investigation would be a collaborative effort between the University of California, Berkeley; UCLA; the University of Colorado and the University of Iowa. Additional information on reconnection and ISTP can be found on the web at: http://www-st.physics.uiowa.edu/www/html/press/video.html.
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