Evidence of energy and charge sign dependence of the recovery time for the 2006 December Forbush event measured by the PAMELA experiment
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Date
2018Author
Munini, R.
Potgieter, M.S.
Boezio, M.
Bruno, A.
Christian, E.C.
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New results on the short-term galactic cosmic-ray (GCR) intensity variation (Forbish decrease) in 2006 December
measured by the PAMELA instrument are presented. Forbush decreases are sudden suppressions of the GCR
intensities, which are associated with the passage of interplanetary transients such as shocks and interplanetary
coronal mass ejections (ICMEs). Most of the past measurements of this phenomenon were carried out with groundbased
detectors such as neutron monitors or muon telescopes. These techniques allow only the indirect detection of
the overall GCR intensity over an integrated energy range. For the first time, thanks to the unique features of the
PAMELA magnetic spectrometer, the Forbush decrease, commencing on 2006 December 14 and following a CME
at the Sun on 2006 December 13, was studied in a wide rigidity range (0.4–20 GV) and for different species of
GCRs detected directly in space. The daily averaged GCR proton intensity was used to investigate the rigidity
dependence of the amplitude and the recovery time of the Forbush decrease. Additionally, for the first time, the
temporal variations in the helium and electron intensities during a Forbush decrease were studied. Interestingly, the
temporal evolutions of the helium and proton intensities during the Forbush decrease were found to be in good
agreement, while the low rigidity electrons (<2 GV) displayed a faster recovery. This difference in the electron
recovery is interpreted as a charge sign dependence introduced by drift motions experienced by the GCRs during
their propagation through the heliosphere
URI
http://hdl.handle.net/10394/26431https://doi.org/10.3847/1538-4357/aaa0c8
http://iopscience.iop.org/article/10.3847/1538-4357/aaa0c8/pdf