Dr. Jim Wild (Lancaster University)
| Substorms represent the explosive reconfiguration of the magnetosphere resulting from the release of solar wind energy and momentum stored in the Earth's magnetic tail. They are typically subdivided into three distinct stages, namely the growth, expansion and recovery phases. During the growth phase (usually associated with extended intervals of southward-directed interplanetary magnetic field) reconnection at the dayside magnetopause results in magnetic flux being added to the Earth's magnetotail and the transfer of solar wind energy and momentum into the magnetosphere. At the onset of the expansion phase, an instability prompts the rapid reconfiguration of the magnetotail and results in highly dynamic aurora and enhanced ionospheric currents. The location and timing of expansion phase onset is one of the most significant outstanding questions in solar-terrestrial physics: new results from the THEMIS mission will be discussed that offer clues to the onset region and mechanism. Furthermore, some studies over the last decade have indicated that the instability responsible for substorm expansion phase onset may require an external trigger (i.e. a triggering factor in the solar wind or interplanetary magnetic field). Statistical investigations have lead to contrasting interpretations regarding the relationship between proposed solar wind triggers and substorm onsets identified from geomagnetic data. Results of an investigation into the possible triggering of substorms observed over the 2001-2005 period and exploiting data from the Cluster and IMAGE satellite missions will be presented and compared to earlier studies. Finally, the ionospheric response to magnetospheric substorms, based upon several thousand individual substorms will be discussed. |
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