ASTRONOMICAL BREAKING NEWS – Auroral mechanism

This is the Abstract of the paper published on July 24, 2008, by SCIENCE magazine. The magazine belongs to the American Association for the Advancement of Science, (AAAS).

Tail Reconnection Triggering Substorm Onset

Vassilis Angelopoulos 1*, James P. McFadden 2, Davin Larson 2, Charles W. Carlson 2, Stephen B. Mende 2, Harald Frey 2, Tai Phan 2, David G. Sibeck 3, Karl-Heinz Glassmeier 4, Uli Auster 4, Eric Donovan 5, Ian R. Mann 6, I. Jonathan Rae 6, Christopher T. Russell 1, Andrei Runov 1, Xu-Zhi Zhou 1, Larry Kepko 7

1 IGPP/ESS, UCLA, Los Angeles, CA, USA.
2 Space Sciences Laboratory, University of California at Berkeley, CA, USA.
3 Code 674, NASA/GSFC, Greenbelt, MD, USA.
4 TUBS, Braunschweig, D-38106, Germany.
5 Department of Physics and Astronomy, University of Calgary, Calgary, Canada.
6 Department of Physics, University of Alberta, Edmonton, Alberta, Canada.
7 Space Science Center, University of New Hampshire, Durham, NH, USA.

* To whom correspondence should be addressed to: Vassilis Angelopoulos, e-mail: vassilis@ucla.edu

 

Magnetospheric substorms explosively release solar wind energy previously stored in Earth’s magnetotail, encompassing the entire magnetosphere and producing spectacular auroral displays. It has been unclear whether a substorm is triggered by a disruption of the electrical current flowing across the near-Earth magnetotail, at ~10 RE (RE = Earth Radius, or 6374 km), or by the process of magnetic reconnection typically seen farther out in the magnetotail, at ~20 to 30 RE. We report on simultaneous measurements in the magnetotail at multiple distances, at the time of substorm onset. Reconnection was observed at 20 RE, at least 1.5 min before auroral intensification, at least 2 min before near-Earth current disruption, and about 3 min before substorm expansion. These results demonstrate that substorms are likely initiated by tail reconnection.