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The Unusual Behavior of Anomalous and Galactic Cosmic Ray Intensities at 1 AU During the Present Solar Minimum

Leske, R. A. and Cummings, A. C. and Cohen, C. M. S. and Mewaldt, R. A. and Stone, E. C. and Wiedenbeck, M. E. and von Rosenvinge, T. T. (2009) The Unusual Behavior of Anomalous and Galactic Cosmic Ray Intensities at 1 AU During the Present Solar Minimum. In: Proceedings of the 31st International Cosmic Ray Conference. , Lodz, Poland. https://resolver.caltech.edu/CaltechAUTHORS:20150527-091845568

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Abstract

Since the early 1970's, anomalous cosmic ray (ACR) intensities at 1 AU at solar minimum have generally tracked the galactic cosmic ray (GCR) intensities as measured by neutron monitors. Throughout the current A<0 cycle, however, the ACR intensities are a factor of 3-4 lower than expected from scaling neutron monitor rates; a similar discrepancy seems to have been present during the last A<0 period in the mid-1980's. Also, although there have been no major solar particle events for over 2 years, and sunspot numbers have been at minimum levels for at least a year, the ACR intensities are at present a factor of ~2 lower than their maximum values during each of the last 3 solar minima, suggesting that heliospheric conditions are not yet at minimum modulation levels. This is probably associated with the fact that ACRs drift inward along the heliospheric current sheet (HCS) during A<0 cycles, and the tilt of the current sheet is still relatively high (~23�) for solar minimum. However, while ACR intensities are low, GCR intensities are at a record high, and compared with the last A<0 cycle, we find that both ACR and GCR intensities are actually much higher now for a given HCS tilt angle than they were in the mid-1980's.


Item Type:Book Section
Related URLs:
URLURL TypeDescription
http://icrc2009.uni.lodz.pl/proc/pdf/icrc0536.pdfOrganizationArticle
ORCID:
AuthorORCID
Leske, R. A.0000-0002-0156-2414
Cummings, A. C.0000-0002-3840-7696
Cohen, C. M. S.0000-0002-0978-8127
Mewaldt, R. A.0000-0003-2178-9111
Stone, E. C.0000-0002-2010-5462
Wiedenbeck, M. E.0000-0002-2825-3128
Additional Information:Copyright University of Łódź. Department of High Energy Astrophysics, 2010. This work was supported by NASA grant NNX08AI11G. The Newark neutron monitor of the Bartol Research Institute is supported by NSF grant ATM-0527878. We thank the Wilcox Solar Observatory for making the HCS data publicly available [7], and acknowledge the ACE/SWEPAM team and ACE Science Center for the SWEPAM solar wind data.
Group:Space Radiation Laboratory
Funders:
Funding AgencyGrant Number
NASANNX8AI11G
NSFATM-0527878
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Space Radiation Laboratory2009-22
Record Number:CaltechAUTHORS:20150527-091845568
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20150527-091845568
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:57848
Collection:CaltechAUTHORS
Deposited By: Deborah Miles
Deposited On:01 Jun 2015 23:40
Last Modified:09 Mar 2020 13:19

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