Multiple Spacecraft Observations of the Major Geomagnetic Storm on 31 March 2001

Daniel N. Baker (LASP/U. of Colorado, Boulder, CO, 80303-7814), 
Scot R. Elkington, Michael J. Wiltberger, Robert S. Weigel
 

Early on March 31, 2001 a strong interplanetary shock wave struck the Earth,
initiating one of the largest geomagnetic storms of this solar cycle (minimum
Dst=-360 nT at 0900 UT on March 31). Direct observations near geostationary
orbit showed that the magnetopause, and very probably even the EarthÕs bow
shock, were pushed inside 6.6 Re geocentric distance. Such an extreme
magnetospheric global "compressionÕÕ is very rare. On March 31 at 0635 UT when
the CLUSTER constellation was near local midnight and at 4 Re geocentric
distance, sensors observed an energetic electron injection event associated with
a strong (AE =1500 nT) magnetospheric substorm. Geostationary spacecraft
1991-080 located at 20 LT also saw an abrupt electron injection event at 0630 UT
and FAST spacecraft instruments 19 LT) detected a powerful set of magnetic
field, electric field, and energetic plasma signatures at 0637 UT. GOES 8 and 10
(which bracketed local midnight) saw strong magnetic field depolarization events
at this same time. The energetic neutral atom imaging experiments onboard the
IMAGE spacecraft detected an injection of substorm-produced 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 constellation
together with IMAGE and the other well-placed spacecraft provide the
telescope-microscope combination that is the long-sought realization of a major
magnetospheric research objective. This shows particularly the power of
localized multi-point measurements from CLUSTER. We report the wide range of
observations in this case and relate those observations to the global MHD
simulation our team has performed for the 31 March event.

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Presented at the August 2003 AGU Chapman Conference, Helsinki, Finland