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Two Distinct Plasma and Energetic Ion Distributions within the June 1998
On June 24-25, 1998 a magnetic cloud was observed by ACE near the
L1 Lagrangian point. On the basis of magnetic field data the cloud
contains what at first appears to be a single interplanetary magnetic field
(IMF) flux rope. However, within this flux rope we find two distinct
distributions of plasma and energetic particles. The first region
of the cloud is populated with anti-sunward streaming energetic ions and
suprathermal electrons and exhibits a low alpha to proton ratio, typical
of the solar wind. Halfway into the magnetic cloud a second and distinct
spatial region was encountered, demarcated by a significant drop in the
proton temperature and increase in the alpha to proton ratio, as well as
an increase in the proton density, consistent with the second region being
populated with photospheric material. This second region was also
populated with bidirectional suprathermal electron pitch angle distributions
(PADs) and "pancake" energetic ion PADs. Therefore not only are the
two regions within the flux rope occupied by two different plasma regimes,
implying different coronal origins, but the electron and ion anisotropies
are completely different, (unidirectional vs. bidirectional), implying
markedly different global topologies for the magnetic field lines.
Authors: D. K. Haggerty, E. C. Roelof ,C. W.
Smith, N. F. Ness, R. M. Skoug, R. L. Tokar, R. A. Howard, M. D. Andrews
Organization: The Johns Hopkins University Applied Physics Laboratory
Address: 11100 Johns Hopkins Road
Laurel, MD 20723-6099
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