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Title: Variations in the Inferred Cosmic-Ray Spectral Index as Measured by Neutron Monitors in Antarctica
Abstract A technique has recently been developed for tracking short-term spectral variations in Galactic cosmic rays (GCRs) using data from a single neutron monitor (NM), by collecting histograms of the time delay between successive neutron counts and extracting the leader fractionLas a proxy of the spectral index. Here we analyzeLfrom four Antarctic NMs from 2015 March to 2023 September. We have calibratedLfrom the South Pole NM with respect to a daily spectral index determined from published data of GCR proton fluxes during 2015–2019 from the Alpha Magnetic Spectrometer (AMS-02) on board the International Space Station. Our results demonstrate a robust correlation between the leader fraction and the spectral index fit over the rigidity range 2.97–16.6 GV for AMS-02 data, with uncertainty of 0.018 in the daily spectral index as inferred fromL. In addition to the 11 yr solar activity cycle, a wavelet analysis confirms a 27 day periodicity in the GCR flux and spectral index corresponding to solar rotation, especially near sunspot minimum, while the flux occasionally exhibits a strong harmonic at 13.5 days. The magnetic field component along a nominal Parker spiral (i.e., the magnetic sector structure) is a strong determinant of such spectral and flux variations, with the solar wind speed exerting an additional, nearly rigidity-independent influence on flux variations. Our investigation affirms the capability of ground-based NM stations to accurately and continuously monitor cosmic-ray spectral variations over the long-term future.  more » « less
Award ID(s):
2112437
PAR ID:
10621819
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ;
Publisher / Repository:
Published by the American Astronomical Society
Date Published:
Journal Name:
The Astrophysical Journal
Volume:
974
Issue:
2
ISSN:
0004-637X
Page Range / eLocation ID:
284
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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