ESA Science & Technology11-Jul-2005 10:07:11

Science Results

Telescopic/Microscopic view of a substorm

The Solar storm viewed by the Telescope (IMAGE) and the microscope (Cluster) (from D. Baker et al., Geophys. Res. Lett, 2002.

A powerful solar eruption occurred on 29 March 2001, which then released a coronal mass ejection toward the Earth. Early on 31 March 2001, since it is taking about 2 days for the CME to reach the Earth, a strong interplanetary shock struck the Earth, initiating one of the largest geomagnetic storms of this solar cycle. The magnetopause, and very probably even the Earth's bow shock, were pushed inside the geostationary orbit (6.6 Earth Radii (RE) geocentric distance). Such an extreme magnetospheric global ''compression'' is very rare.

A schematic summary of the substorm onset events at 0635 UT on March 31, 2001 (from D. Baker et al., Geophys. Res. Lett, 2002).

The Cluster constellation was near local midnight and at 4 RE geocentric distance, sensors observed an energetic electron injection event associated with a strong magnetospheric substorm. The energetic neutral atom imaging experiments onboard the IMAGE spacecraft detected an injection of ions in the pre-midnight sector commencing at 0630 UT. Electron injection signatures at the four separate Cluster locations allow us to infer the location, speed, and direction of the substorm injection boundary. Hence, the Cluster (and IMAGE) telescope-microscope combination is a long-sought realization of a major magnetospheric research objective and shows the power of localized multipoint measurements from Cluster. These results were published in D. Baker et al., Geophys. Res. Lett, 2002.

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