AGU: Geophysical Research Letters

 

Editors' Highlight

Ballooning instabilities: Triggers of geomagnetic substorms?

Geomagnetic substorms are driven by variations on the Sun and can disrupt satellite systems, produce aurorae, and increase the radiation dose of astronauts and passengers on transpolar flights. Right before the onset of a geomagnetic substorm, a large upsurge in duskward ion flux occurs that some scientists believe excites cross-field current instabilities and possibly triggers substorm expansion. Saito et al. (2008) sought to discover whether this ballooning instability influences the magnetotail near Earth in the late-growth stage of substorms. Using data from the joint Japan/U.S. Geotail satellite, the authors determined that the ballooning instability deforms magnetic field lines in the magnetotail, producing magnetic field fluctuations. Further examination of a set of six substorms that were detected in the vicinity of the magnetic equator revealed that that ballooning mode was identified in cases where plasma flow velocities were high. From this knowledge of the plasma flow velocity, the scientists were able to estimate the wavelength of the instabilities. The authors expect that such studies will help scientists better predict geomagnetic substorms.

View abstract

View full article (Subscription required)