Telescopic and Microscopic views of the Magnetosphere: Multispacecraft Observations

Baker, D. N.

	The magnetospheric research community has long sought the capability to view the
Sun-Earth system in a global way and concurrently to probe the microphysical details
of key physical regions. This objective has now been substantially realized with the
combination of the CLUSTER and IMAGE missions. With the additional use of SOHO, ACE,
FAST, SAMPEX, POLAR, and geostationary orbit spacecraft, there is a remarkable
ability to apply both telescopic and microscopic principles. As an example, a bright
active region on the Sun gave rise on 29 March 2001 to a fast halo coronal mass
ejection (CME) event observed by SOHO instruments. Subsequently on 31 March, a
strong interplanetary shock wave ahead of a magnetic cloud (probably arising from
the earlier CME) passed the ACE spacecraft and hit the EarthÕs magnetosphere. This
driver compressed the subsolar magnetopause to ²4 RE geocentric distance and
initiated a powerful geomagnetic storm (minimum Dst ~ -360 nT). The CLUSTER II set
of four spacecraft were located in the midnight sector of the magnetosphere near
perigee (r~4 RE) at ~0635 UT and observed a dispersionless injection of energetic
(E³20 keV) electrons in association with a large magnetospheric substorm expansion
phase onset (AE ~1200 nT). A Los Alamos geostationary spacecraft located at ~20 LT
(1991-080) observed a strong electron injection event commencing at ~0630 UT,
confirming the timing of the substorm onset. At ~0637 UT, the FAST spacecraft at
~1800 km altitude and ~19 MLT saw a powerful field-aligned current signature and a
perpendicular electric field of ~60 mV/m at an invariant latitude of ~60ûS.
Concurrent to these in situ observations, the IMAGE spacecraft was returning a
sequence of global Energetic Neutral Atom (ENA) images from the medium-energy (MENA)
and high-energy (HENA) sensor systems. These data showed a very prominent injection
of substorm ions in the premidnight (and postdusk) sector of the inner
magnetosphere.  This event is consistent with a substorm onset that pushed the
substorm "injection boundary" far inside of geostationary orbit and far toward the
dusk sector. The CLUSTER data, especially, reveal microphysical details of the
injection boundary properties. Together, this armada of spacecraft gave an
unprecedented view both telescopically and microscopically of a powerful
magnetospheric substorm during the main phase development of a major geomagnetic
storm. This and many other available events reveal the power of multispacecraft
observations.

_______________
To be presented at the Magnetospheric Imaging Workshop, 
Yosemite National Park, California, U.S.A., Feb. 5-8, 2002.