Opening a Window on ICME-driven GCR Modulation in the Inner Solar System

Author
Keywords
Abstract
<p>Interplanetary coronal mass ejections (ICMEs) often cause Forbush decreases (Fds) in the flux of galactic cosmic rays (GCRs). We investigate how a single ICME, launched from the Sun on 2014 February 12, affected GCR fluxes at Mercury, Earth, and Mars. We use GCR observations from MESSENGER at Mercury, ACE/LRO at the Earth/Moon, and MSL at Mars. We find that Fds are steeper and deeper closer to the Sun, and that the magnitude of the magnetic field in the ICME magnetic ejecta as well as the \textquotedblleftstrength\textquotedblright of the ICME sheath both play a large role in modulating the depth of the Fd. Based on our results, we hypothesize that (1) the Fd size decreases exponentially with heliocentric distance, and (2) that two-step Fds are more common closer to the Sun. Both hypotheses will be directly verifiable by the upcoming Parker Solar Probe and Solar Orbiter missions. This investigation provides the first systematic study of the changes in GCR modulation as a function of distance from the Sun using nearly contemporaneous observations at Mercury, Earth/Moon, and Mars, which will be critical for validating our physical understanding of the modulation process throughout the heliosphere.</p>
Year of Publication
2018
Journal
The Astrophysical Journal
Volume
856
Number
Number of Pages
139
Date Published
04/2018
URL
http://stacks.iop.org/0004-637X/856/i=2/a=139?key=crossref.287f3cbc519cdfae455bd8b9d0a9351a
DOI
10.3847/1538-4357/aab098