Topology and Dynamics of the 12 December 1980 Magnetic Cloud Event

In this work we have performed an analysis of the interplanetary magnetic field and plasma parameters associated with the 12th December 1980 shock–magnetic cloud event. The study was complemented by including a detailed analysis of the energetic particles fluxes, spectral indexes and directional information. Locally, the magnetic cloud had a latitude of 48°, longitude of 220° and a radius of 0.15 AU. The maximum approach of the ISEE-3 spacecraft to the magnetic cloud axis was 0.047 AU. Moreover, our results suggest that, when encountered by the spacecraft, the magnetic cloud was expanding at a rate of roughly r ₁/r ₀=1.5 (r ₁ is the final radius and r ₀ the initial one) and that it had been expanding during 59 hr. We have also found evidence which indicates that the particle injection inside the cloud depended on the particle energy and pitch angle. These features also suggest that the energetic particle bi-directional fluxes could not be produced by mirroring in the magnetic cloud feet. Instead we think that these fluxes could be generated by the intrinsic properties of the injection mechanism.