Evidence for a Time Lag in Solar Modulation of Galactic Cosmic Rays

Tomassetti, Nicola; Orcinha, M.; Barão, F.; Bertucci, B.

doi:10.3847/2041-8213/aa9373

Cited by 64 publications

(70 citation statements)

References 55 publications

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“…This approach means that the model is diffusion dominated, rather than drift dominated as the original drift models of the 1980s and 1990s were, and also as recently applied by e.g. Tomassetti et al (2017).…”

Section: Diffusion and Drift Coefficientsmentioning

confidence: 99%

Numerical Modeling of Galactic Cosmic-Ray Proton and Helium Observed by AMS-02 during the Solar Maximum of Solar Cycle 24

Corti¹,

Potgieter²,

Bindi³

et al. 2019

ApJ

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Galactic cosmic rays (GCRs) are affected by solar modulation while they propagate through the heliosphere. The study of the time variation of GCR spectra observed at Earth can shed light on the underlying physical processes, specifically diffusion and particle drifts. Recently, the AMS-02 experiment measured with very high accuracy the time variation of the cosmic ray proton and helium flux between May 2011 and May 2017 in the rigidity range from 1 to 60 GV. In this work, a comprehensive three-dimensional (3D) steady-state numerical model is used to solve Parker's transport equation and is used to reproduce the monthly proton fluxes observed by AMS-02. We find that the rigidity slope of the perpendicular mean free path above 4 GV remains constant, while below 4 GV it increases during solar maximum. Assuming the same mean free paths for helium and protons, the models are able to reproduce the time behavior of the p/He ratio observed by AMS-02. The dependence of the diffusion tensor on the particle mass-to-charge ratio, A/Z, is found to be the main cause of the time dependence of p/He below 3 GV.

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Section: Diffusion and Drift Coefficientsmentioning

confidence: 99%

Numerical Modeling of Galactic Cosmic-Ray Proton and Helium Observed by AMS-02 during the Solar Maximum of Solar Cycle 24

Corti¹,

Potgieter²,

Bindi³

et al. 2019

ApJ

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“…13 HELMOD parameters-usually determined at 1 au-are used for the properties of any heliospheric sector, according to the time required by the solar wind coming from the Sun to reach such a region Boschini et al 2017a). When this is not accounted for there is an effective time delay in the correlation between time variations of the parameters of the solar magnetic field, as measured at Earth, and the observed intensity variations of GCRs (see, e.g., Tomassetti et al 2017, and references therein).…”

Section: Interstellar Propagationmentioning

confidence: 99%

HelMod in the Works: From Direct Observations to the Local Interstellar Spectrum of Cosmic-Ray Electrons

Boschini

Torre

Gervasi

et al. 2018

ApJ

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The local interstellar spectrum (LIS) of cosmic-ray (CR) electrons for the energy range 1 MeV to 1 TeV is derived using the most recent experimental results combined with the state-of-the-art models for CR propagation in the Galaxy and in the heliosphere. Two propagation packages, GALPROP and HELMOD, are combined to provide a single framework that is run to reproduce direct measurements of CR species at different modulation levels, and at both polarities of the solar magnetic field. An iterative maximum-likelihood method is developed that uses GALPROP-predicted LIS as input to HELMOD, which provides the modulated spectra for specific time periods of the selected experiments for model-data comparison. The optimized HelMod parameters are then used to adjust GALPROP parameters to predict a refined LIS with the procedure repeated subject to a convergence criterion. The parameter optimization uses an extensive data set of proton spectra from 1997 to 2015. The proposed CR electron LIS accommodates both the low-energy interstellar spectra measured by Voyager 1 as well as the high-energy observations by PAMELA and AMS-02 that are made deep in the heliosphere; it also accounts for Ulysses counting rate features measured out of the ecliptic plane. The interstellar and heliospheric propagation parameters derived in this study agree well with our earlier results for CR protons, helium nuclei, and anti-protons propagation and LIS obtained in the same framework.

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“…Inspecting the relation betweenκ 0 j and the "delayed" SSN revealed a correlation coefficient of ρ ∆T = −0.89 against the ρ 0 = −0.66 for the scenario of ∆T = 0. Figures for both ∆T = 8.1 months and ∆T = 0 scenarios can be found in [35].…”

Section: Resultsmentioning

confidence: 99%

Observation of a time lag in solar modulation of cosmic rays in the heliosphere

Orcinha

Tomassetti

Barão

et al. 2019

J. Phys.: Conf. Ser.

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The solar modulation effect of Galactic cosmic rays is a time-dependent phenomenon that is caused by the transport of these particles through the magnetized plasma of the heliosphere. Using a data-driven model of cosmic-ray transport in the heliosphere, in combination with a large collection of data, we report the evidence for a eight-month time lag between observations of solar activity and measurements of cosmic-ray fluxes in space. As we will discuss, this result enables us to forecast the cosmic ray flux at Earth well in advance by monitoring solar activity. We also compare our predictions with the new multi-channel measurements of cosmic rays operated by the AMS experiment in space.

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Evidence for a Time Lag in Solar Modulation of Galactic Cosmic Rays

Cited by 64 publications

References 55 publications

Numerical Modeling of Galactic Cosmic-Ray Proton and Helium Observed by AMS-02 during the Solar Maximum of Solar Cycle 24

Numerical Modeling of Galactic Cosmic-Ray Proton and Helium Observed by AMS-02 during the Solar Maximum of Solar Cycle 24

HelMod in the Works: From Direct Observations to the Local Interstellar Spectrum of Cosmic-Ray Electrons

Observation of a time lag in solar modulation of cosmic rays in the heliosphere

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