Other
Scientific paper
May 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusmsm42a..08s&link_type=abstract
American Geophysical Union, Spring Meeting 2002, abstract #SM42A-08
Other
2720 Energetic Particles, Trapped, 2740 Magnetospheric Configuration And Dynamics, 2778 Ring Current, 2788 Storms And Substorms
Scientific paper
During geomagnetic storms the fluxes of energetic particles observed at geosynchronous orbit often exhibit a "sawtooth" profile, with quasi-periodic repetitions of sudden flux increases followed by gradual but dramatic decreases in flux. Some studies have suggested that each sawtooth is caused by a substorm injection, while others have suggested that they instead represent some sort of global oscillation of the magnetosphere. In this study, we examine the nature of sawtooth flux variations observed from July 2000 to December 2001 using a combination of in situ observations from geosynchronous satellites and global energetic neutral atom (ENA) and UV images from the IMAGE spacecraft. We find that sawtooth events appear to be substorms on a more global scale. These events show the auroral signatures of substorms, increases in the global particle flux, and increases in the sym-H index (sym-H becomes less negative) at the flux increases. Each sawtooth enhancement is first observed near midnight, and the events then propagate rapidly around the Earth at speeds exceeding the particle drift speeds. Sawtooth enhancements tend to occur during times of moderate solar wind driving. The geomagnetic field stretches during the decay phase of each sawtooth, and dipolarizes at each flux increase. The dipolarizations are often very large (20-50 degrees), and are observed at nearly all local times, again showing the global nature of these events. In addition, variations in the azimuthal angle of the geomagnetic field are also observed at sawtooth enhancements. We examine the implications of these magnetic field variations for the current systems responsible for sawtooth enhancements.
Borovsky Joseph E.
C:son Brandt Pontus
Funsten Herbert O.
Henderson Gideon M.
Jahn J.-
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