Two Distinct Plasma and Energetic Ion Distributions within the June 1998 Magnetic Cloud
D. K. Haggerty, E. C. Roelof 
The Johns Hopkins University Applied Physics laboratory, Laurel MD 20723

C. W. Smith, N. F. Ness
Bartol Research Institute, University of Delaware, Newark DE 19716

R. M. Skoug, R. L. Tokar
Los Alamos National Laboratory, Los Alamos, NM 87545

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 n ot 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.