Drift Effects on the Galactic Cosmic Ray Modulation

Abstract

Cosmic ray (CR) modulation is driven by both solar activity and drift effects in the heliosphere, although their role is only qualitatively understood as it is difficult to connect the CR variations to their sources. In order to address this problem, the Empirical Mode Decomposition technique has been applied to the CR intensity, recorded by three neutron monitors at different rigidities (Climax, Rome, and Huancayo-Haleakala (HH)), the sunspot area, as a proxy for solar activity, the heliospheric magnetic field magnitude, directly related to CR propagation, and the tilt angle (TA) of the heliospheric current sheet (HCS), which characterizes drift effects on CRs. A prominent periodicity at ∼six years is detected in all the analyzed CR data sets and it is found to be highly correlated with changes in the HCS inclination at the same timescale. In addition, this variation is found to be responsible for the main features of the CR modulation during periods of low solar activity, such as the flat (peaked) maximum in even (odd) solar cycles. The contribution of the drift effects to the global Galactic CR modulation has been estimated to be between 30% and 35%, depending on the CR particle energy. Nevertheless, the importance of the drift contribution is generally reduced in periods nearing the sunspot maximum. Finally, threshold values of ∼40 • , ∼45 • , and >55 • have been derived for the TA, critical for the CR modulation at the Climax, Rome, and HH rigidity thresholds, respectively.

Observational evidence for buffeting-induced kink waves in solar magnetic elements

“…The EMD technique has already been used in many contexts of solar physics, heliospheric and magnetospheric physics such as, but not limited to, the study of coronal oscillations (Terradas et al 2004), neutrino flux modulation (Vecchio et al 2010(Vecchio et al , 2012, cosmic rays modulation (Laurenza et al 2014), and magnetospheric studies (De Michelis et al 2012). …”

Study of Cosmic-Ray Modulation During the Recent Unusual Minimum and Mini-Maximum of Solar Cycle 24

“…The long-term GCR modulation shows an ≈ 22-year cycle related to the solar magnetic cycle as the solar polarity reverses near solar maximum of every activity cycle. The polarity dependent effects on cosmic rays have also been an area of active research (e.g., Jokipii, Levy, and Hubbard, 1977;Potgieter and Moraal, 1985;Smith and Thomas, 1986;Cliver and Ling, 2001;Kota 2013;Potgieter, 2014;Laurenza et al, 2014;Potgieter et al, 2014;and references therein).…”

Characteristics and Energy Dependence of Recurrent Galactic Cosmic-Ray Flux Depressions and of a Forbush Decrease with LISA Pathfinder

“…Both were extensively studied in the last 60 years on Earth with neutron monitors and in space (Forbush 1954(Forbush , 1958Storini et al 1992;Beer 2000;Clem & Evenson 2004;Ferreira et al 2004;Grimani 2004Grimani , 2007Hajadas et al 2004;Grimani et al 2007;Shikaze et al 2007;Sabbah & Kudela 2011;Usoskin et al 2011Usoskin et al , 2017Laurenza et al 2012Laurenza et al , 2014.…”