Grad-Shafranov reconstruction of a magnetic cloud: Effects of the magnetic-field topology on the galactic cosmic-ray intensity

The passage of the interplanetary counterpart of a coronal mass ejection was observed at L1 between 2016 August 2 at 14:00 UT and August 3 at 03:00 UT. The transit of shock, sheath and magnetic cloud (MC) regions are identified and the MC configuration is studied through the Grad-Shafranov reconstruction technique. A classical Forbush decrease (FD) in the galactic cosmic ray (GCR) intensity was observed by the particle detector (PD) aboard the European Space Agency LISA Pathfinder (LPF) mission on 2016 August 2. The PD allowed to monitor the GCR intensity at energies above 70 MeV n−1 with a statistical uncertainty of 1% on one-hour binned data. The observed fractional decrease of the GCR intensity around the dip of the event is investigated through a full-orbit particle propagation in the MC and related to the reconstructed magnetic field topology