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Average spatial distribution of cosmic rays behind the interplanetary shock - global muon detector network observations


Kozai, M and Munakata, K and Kato, C and Kuwabara, T and Rockenbach, M and Dal Lago, A and Schuch, NJ and Braga, CR and Mendonca, RRS and Al Jassar, HK and Sharma, MM and Duldig, ML and Humble, JE and Evenson, P and Sabbah, I and Tokumaru, M, Average spatial distribution of cosmic rays behind the interplanetary shock - global muon detector network observations, Astrophysical Journal, 825, (2) Article 100. ISSN 0004-637X (2016) [Refereed Article]


Copyright Statement

© 2016. The American Astronomical Society. All rights reserved.

DOI: doi:10.3847/0004-637X/825/2/100


We analyze the galactic cosmic ray (GCR) density and its spatial gradient in Forbush Decreases (FDs) observed with the Global Muon Detector Network (GMDN) and neutron monitors (NMs). By superposing the GCR density and density gradient observed in FDs following 45 interplanetary shocks (IP-shocks), each associated with an identified eruption on the Sun, we infer the average spatial distribution of GCRs behind IP-shocks. We find two distinct modulations of GCR density in FDs, one in the magnetic sheath and the other in the coronal mass ejection (CME) behind the sheath. The density modulation in the sheath is dominant in the western flank of the shock, while the modulation in the CME ejecta stands out in the eastern flank. This east–west asymmetry is more prominent in GMDN data responding to ~60 GV GCRs than in NM data responding to ~10 GV GCRs, because of the softer rigidity spectrum of the modulation in the CME ejecta than in the sheath. The geocentric solar ecliptic-y component of the density gradient, Gy, shows a negative (positive) enhancement in FDs caused by the eastern (western) eruptions, while Gz shows a negative (positive) enhancement in FDs caused by the northern (southern) eruptions. This implies that the GCR density minimum is located behind the central flank of IP-shocks and propagating radially outward from the location of the solar eruption. We also confirmed that the average Gz changes its sign above and below the heliospheric current sheet, in accord with the prediction of the drift model for the large-scale GCR transport in the heliosphere.

Item Details

Item Type:Refereed Article
Keywords:cosmic rays, interplanetary medium, solar wind, coronal mass ejections (CMEs)
Research Division:Physical Sciences
Research Group:Astronomical sciences
Research Field:High energy astrophysics and galactic cosmic rays
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the physical sciences
UTAS Author:Duldig, ML (Dr Marc Duldig)
UTAS Author:Humble, JE (Dr John Humble)
ID Code:110212
Year Published:2016
Web of Science® Times Cited:4
Deposited By:Mathematics and Physics
Deposited On:2016-07-20
Last Modified:2017-11-03
Downloads:185 View Download Statistics

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