Cosmic ray angular distribution dynamics during Forbush decrease in 3-4 November 2021

P.Yu. Gololobov, V.G. Grigoryev, S.A. Starodubtsev, S.K. Gerasimova, A.S. Zverev, ShICRA SB RAS, Russia

In 3-4 November 2021 a coronal mass ejection (CME) has passed through the Earth. According to the direct measurements of the interplanetary magnetic field and solar wind parameters the CME was accompanied by a magnetic cloud. During this event the NMDB neutron monitors have registered a two step Forbush decrease with a total amplitude up to 15 %. Preliminary analysis of the NMDB data shows that the first step was caused by the depression of cosmic ray (CR) density in the shock front while the second step was caused by an anisotropy formed inside the magnetic cloud. The current work is aimed to study the dynamics of the angular distribution of CR during this event. Derivation of the CR angular distribution is performed using the global survey method developed in ShICRA SB RAS in 1960s. The method allows using the world network of neutron monitors as a single multidirectional device and get hour to hour dynamics of CR angular distribution. It is shown that inside the magnetic cloud both unidirectional and bidirectional anisotropies of CR with significant amplitudes were formed. The obtained results are discussed in the frames of modern theories of magnetic clouds.

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