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Descrizione
The galactic cosmic ray (GCR) intensity is modulated by solar activity and represents indirect probe of the heliospheric conditions. For instance, the GCR intensity follows the approximately 11-year solar cycle, exhibiting a well-known anti-correlation with solar activity. At short-term time scales, Forbush decreases (FDs), i.e. GCR intensity ranging from hours to days are driven by transient solar wind structures, such as interplanetary coronal mass ejections (ICMEs).
Understanding the link between long and short-term variations is essential for a comprehensive description of solar activity, heliospheric environment and space weather–space climate coupling. A particularly interesting feature emerging at solar maximum is the temporary decrease in solar activity known solar cycle double-peak or Gnevyshev gap (GG).
We investigated the specific relation between the occurrence of FDs and the solar activity cycle characteristics, including GG, over the course of five solar cycles. The GCR intensity data are provided by the SVIRCO (Studio delle Variazioni dell’Intensità dei Raggi COsmici) Observatory, i.e. the neutron monitor located in Rome (Italy), having a geomagnetic cutoff of 6.27 GV.
We perform a statistical analysis of the occurrence of CME and geoeffective ICME as a major driver of FDs, showing similarities and differences with respect to FD occurrence during the different phases of the solar cycles. We discuss how the frequency and magnitude of FDs evolve in response to the structuring of the solar cycle. Our results confirm the existence of the GG in the FD occurrence and highlight a dependence on the odd-even parity of the solar cycles[M.
| Sessione | Eliofisica e Space Weather |
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