How are Forbush decreases related with IP magnetic field enhancements?

K. P. Arunbabu 1, P. Subramanian1 , Sunil Gupta 2, H. M. Antia 2
1Indian Institute of Science Education and Research, Sai Trinity Building, Pashan, Pune 411 021, India
2Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005, India

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Cosmic ray Forbush decreases (FDs) are usually thought to be due to Earth-directed coronal mass ejections (CMEs) from the Sun and their associated shocks. When CMEs and their shocks reach the Earth, they cause magnetic field compressions. We investigate the relation between these magnetic field compressions and FDs at rigidities between 12 and 42 GV using data from the GRAPES-3 instrument at Ooty. We find that the shapes of the Forbush decrease profiles show a startling similarity to that of the magnetic field compression in the near-Earth IP medium. We seek to understand the implications of this interesting result.

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Keywords : Forbush decrease – CMEs – interplanetary magnetic field