Helium fluxes measured by the PAMELA experiment from the minimum to the maximum solar activity for solar cycle 24

Abstract

Time-dependent energy spectra of galactic cosmic rays (GCRs) carry fundamental information regarding their origin and propagation. When observed at the Earth, these spectra are significantly affected by the solar wind and the embedded solar magnetic field that permeates the heliosphere, changing significantly over an 11-year solar cycle. Energy spectra of GCRs measured during different epochs of solar activity provide crucial information for a thorough understanding of solar and heliospheric phenomena. The PAMELA experiment had collected data for almost ten years (15th June 2006 - 23rd January 2016), including the minimum phase of solar cycle 23 and the maximum phase of solar cycle 24. In this paper, we present new spectra for helium nuclei measured by the PAMELA instrument from January 2010 to September 2014 over a three Carrington rotation time basis. These data are compared to the PAMELA spectra measured during the previous solar minimum providing a picture of the time dependence of the helium nuclei fluxes over a nearly full solar cycle. Time and rigidity dependencies are observed in the proton-to-helium flux ratios. The force-field approximation of the solar modulation was used to relate these dependencies to the shapes of the local interstellar proton and helium-nuclei spectra.

9 pages, 5 figures

References in corpus (5)

• PAMELA - A Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics
• Time dependence of the electron and positron components of the cosmic radiation measured by the PAMELA experiment between July 2006 and December 2015
• Validation of the neutron monitor yield function using data from AMS-02 experiment, 2011--2017
• Testing diffusion of cosmic rays in the heliosphere with proton and helium data from AMS
• Time dependence of the flux of helium nuclei in cosmic rays measured by the PAMELA experiment between July 2006 and December 2009

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• A cosmic-ray database update: CRDB v4.1
• On the Role of ${}^{40}$K in the Origin of Terrestrial Life
• A forecasting framework for galactic cosmic ray flux in space weather applications