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The Ground-level Enhancements of 1989 September 29 and October 22

Published online by Cambridge University Press:  25 April 2016

M.L. Duldig ,
J.L. Cramp ,
J.E. Humble ,
J.W. Bieber ,
P. Evenson ,
K.B. Fenton ,
A.G. Fenton  and
M.B.M. Bendoricchio
M.L. Duldig
Affiliation:
Australian Antarctic Division, c/o Physics Department, University of Tasmania, GPO Box 252C, Hobart, Tas 7001
J.L. Cramp
Affiliation:
Physics Department, University of TasmaniaD.F. Smart, M.A. Shea, Geophysics Directorate, Phillips Laboratories, USA
J.E. Humble
Affiliation:
Physics Department, University of TasmaniaD.F. Smart, M.A. Shea, Geophysics Directorate, Phillips Laboratories, USA
J.W. Bieber
Affiliation:
Bartol Research Institute, University of Delaware, USA
P. Evenson
Affiliation:
Bartol Research Institute, University of Delaware, USA
K.B. Fenton
Affiliation:
Physics Department, University of Tasmania, Hobart
A.G. Fenton
Affiliation:
Physics Department, University of Tasmania, Hobart
M.B.M. Bendoricchio
Affiliation:
Physics Department, University of Tasmania, Hobart
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Abstract

During the solar maximum of 1989–91 an unprecedented sequence of 13 cosmic ray ground-level enhancements (GLEs) was observed by the world-wide neutron monitor network. Of particular interest were two GLEs observed by the Australian network. The 1989 September 29 event was the largest GLE in the space era while the October 22 GLE included an highly anisotropic precursor peak.

Analysis of both these GLEs, taking into account disturbed geomagnetic conditions, shows that the particle arrivals at the earth were unusual. The September 29 GLE had significant particle propagation in the reverse direction and as the particle flux decreased following the peak the spectrum also softened. In contrast, the 1989 October 22 precursor exhibited extreme anisotropy while the particles involved in the main GLE showed a complex temporal structure possibly indicating multiple particle injection at the solar acceleration region.

Type
High Energy Astrophysics
Information
Publications of the Astronomical Society of Australia , Volume 10 , Issue 3 , 1993 , pp. 211 - 217
Copyright
Copyright © Astronomical Society of Australia 1993

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