AVERAGE SPATIAL DISTRIBUTION OF COSMIC RAYS BEHIND THE INTERPLANETARY SHOCK-GLOBAL MUON DETECTOR NETWORK OBSERVATIONS

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Kozai, M. ; Munakata, K. ; Kato, C. ; Kuwabara, T. ; Rockenbach, M. ; Dal Lago, A. ; Schuch, N. J. ; Braga, C. R. ; Mendonca, R. R. S. ; Al Jassar, H. K. ; Sharma, M. M. ; Duldig, M. L. ; Humble, J. E. ; Evenson, P. ; Sabbah, I. ; Tokumaru, M.

• Document type: Journal article
• Source: ASTROPHYSICAL JOURNAL; v. 825, n. 2 JUL 10 2016.
• Web of Science Citations: 3

Abstract

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 similar to 60 GV GCRs than in NM data responding to similar 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, G(y), shows a negative (positive) enhancement in FDs caused by the eastern (western) eruptions, while G(z) 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. (AU)

• FAPESP's process: 12/20594-0 - 1D and 2D analysis of geomagnetic storms precursors using the Gobal Muon Detector Network data
• Grantee: Rafael Rodrigues Souza de Mendonça
• Support Opportunities: Scholarships in Brazil - Doctorate
• FAPESP's process: 08/08840-0 - Study of solar-interplanetary-geomagnetic disturbances using satellite data and Global Muon Detector Network (GMDN) observations for Space Weather applications
• Grantee: Carlos Roberto Braga
• Support Opportunities: Scholarships in Brazil - Master
• FAPESP's process: 14/24711-6 - Study of coronal mass ejections and its corresponding interplanetary structures near the Earth
• Grantee: Carlos Roberto Braga
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 13/02712-8 - Study of interplanetary magnetic structures using cosmic ray data from the global muon detector network
• Grantee: Carlos Roberto Braga
• Support Opportunities: Scholarships abroad - Research Internship - Doctorate
• FAPESP's process: 12/05436-9 - Study of coronal mass ejections and their interplanetary counterparts combining observations of ground cosmic ray detectors and coronagraphs
• Grantee: Carlos Roberto Braga
• Support Opportunities: Scholarships in Brazil - Doctorate
• FAPESP's process: 13/03530-0 - 1D and 2D analysis of geomagnetic storms precursors using the Gobal muon detector network data
• Grantee: Rafael Rodrigues Souza de Mendonça
• Support Opportunities: Scholarships abroad - Research Internship - Doctorate