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Volume 358 - 36th International Cosmic Ray Conference (ICRC2019) - CRD - Cosmic Ray Direct
Interplanetary Magnetic Field Parameters Affecting Cosmic Ray Forbush Decrease
D.M.L. Chauhan,* M.K. Richharia, B. Soni
*corresponding author
Full text: pdf
Pre-published on: 2019 July 22
Published on:
Coronal mass ejections (CMEs) hurl huge volumes of magnetized plasma
into interplanetary space often referred to as ICMEs or ejecta. They are an
important component of solar wind and can cause enhanced geomagnetic
activity when they interact with the Earth’s magnetosphere. When the ejecta
have an average speed greater than the upstream solar wind speed they create a
shock. The large IMF variations due to interplanetary shocks cause depression
in the cosmic ray intensity (CRI) called Forbush Decrease (FD). Large FDs
caused by fast CMEs are specifically associated with energetic X-ray flares. In
the present paper, the author has studied seven largest Forbush decrease events
selected from Moscow Neutron Monitor Station during a period of twelve years
(1996-2008), i.e., 23rd solar cycle. The analysis of CRI data with interplanetary
magnetic field |B|, its southward component Bz, solar wind velocity, Kp and Dst
indices shows that all the three phenomena- solar, interplanetary and
geomagnetic are connected to FD. The relationship between interplanetary
parameters and FDs is discussed in detail. Moreover the solar cycle effect is
found to be slightly shifted for large FDs as the frequency of occurrence of
major FD events is more in the descending phase of the solar cycle.
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