Energetic Ion and Cosmic Ray Characteristics of a Magnetic Cloud

  1. C. T. Russell,
  2. E. R. Priest and
  3. L. C. Lee
  1. T. R. Sanderson1,
  2. J. Beeck1,
  3. R. G. Marsden1,
  4. C. Tranquille1,
  5. K.-P. Wenzel1,
  6. R. B. McKibben2 and
  7. E. J. Smith3

Published Online: 21 MAR 2013

DOI: 10.1029/GM058p0385

Physics of Magnetic Flux Ropes

Physics of Magnetic Flux Ropes

How to Cite

Sanderson, T. R., Beeck, J., Marsden, R. G., Tranquille, C., Wenzel, K.-P., McKibben, R. B. and Smith, E. J. (1990) Energetic Ion and Cosmic Ray Characteristics of a Magnetic Cloud, in Physics of Magnetic Flux Ropes (eds C. T. Russell, E. R. Priest and L. C. Lee), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM058p0385

Author Information

  1. 1

    Space Science Dept. of ESA, Estec, Noordwijk, the Netherlands

  2. 2

    LASR, Enrico Fermi Institute, University of Chicago, Chicago

  3. 3

    Jet Propulsion Laboratory, California Institute of Technology, Pasadena

Publication History

  1. Published Online: 21 MAR 2013
  2. Published Print: 1 JAN 1990

ISBN Information

Print ISBN: 9780875900261

Online ISBN: 9781118663868



  • Solar photosphere;
  • Magnetic flux;
  • Astrophysics


We present energetic ion and magnetic field observations from ISEE-3 and ground based cosmic ray observations from selected neutron monitors, of the magnetic cloud associated with the large interplanetary shock event of February 11, 1982. This shock event had distinct features which included an upstream foreshock, a turbulent downstream region lasting for several hours, and a large magnetic cloud containing bidirectional energetic ion fluxes lasting for several days. Associated with the event was a Forbush decrease observed at the earth. The timing of the onset of the Forbush decrease coincides with the arrival at the earth of the magnetic cloud, and the duration of the decrease corresponds to the duration of the passage of the cloud past the earth. In this event the magnetic cloud appears to be the major cause of the Forbush decrease, whilst the shock and the post-shock turbulent region do not appear to playa major role. Within the cloud we observe highly anisotropic bidirectional energetic ion fluxes and a well ordered magnetic field, both of which signify a large scattering mean free path. The large scattering mean free path suggests that the ions within the magnetic cloud can easily travel along the magnetic field lines, but not across, and therefore, once inside the cloud cannot get out. In the same way, the well ordered magnetic field lines act as a barrier to the cosmic rays crossing the field lines, thereby preventing them from entering into the cloud. The onset of the Forbush decrease occured when the asymptotic arrival direction of the cosmic ray particles for the Deep River, Climax and Huancayo neutron monitors was from an anti-sunward direction. Therefore when the magnetic cloud arrived at the earth, the cosmic rays were immediately prevented from reaching the earth. We conclude that the magnetic cloud is the major cause of the Forbush decrease, whilst the post-shock region plays only a minor role, if any, in this decrease.