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Solar Modulation of Cosmic Nuclei over a Solar Cycle: Results from the Alpha Magnetic Spectrometer
M Aguilar1, B Alpat2, G Ambrosi2
1Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), 28040 Madrid, Spain.
Physical Review Letters
|February 21, 2025
Summary
Galactic cosmic nuclei fluxes exhibit solar cycle variations. Their modulation depends on spectral shape, not velocity, revealing insights into space weather effects.
Area of Science:
- Cosmic ray physics
- Heliophysics
- Astrophysics
Background:
- Galactic cosmic rays (GCRs) are high-energy particles originating outside the solar system.
- Solar activity significantly influences the flux of GCRs reaching Earth.
- Understanding GCR modulation is crucial for space weather prediction and instrument design.
Purpose of the Study:
- To investigate the time variations of cosmic nuclei fluxes (Helium to Oxygen) over an 11-year solar cycle.
- To determine the dependence of solar modulation on nuclear properties like spectral shape and mass-to-charge ratio.
- To provide model-independent insights into the mechanisms of GCR modulation.
Main Methods:
- Analysis of cosmic nuclei fluxes (He, Li, Be, B, C, N, O) from May 2011 to November 2022.
- Measurement of fluxes in the rigidity range of 1.92 to 60.3 GV.
- Correlation analysis between solar modulation amplitudes, spectral indices, and mass-to-charge ratios.
Main Results:
- Cosmic nuclei fluxes show similar, rigidity-dependent time variations over the solar cycle.
- Lower-rigidity Li, Be, B, C, N, and O fluxes are less modulated than Helium.
- Differences in solar modulation correlate linearly with spectral index differences, independent of specific modulation models.
- No significant modulation differences were observed based on the mass-to-charge ratio (A/Z).
Conclusions:
- Solar modulation of galactic cosmic nuclei is primarily dependent on their spectral shape.
- The observed differences in modulation are not explained by velocity dependence on the mass-to-charge ratio.
- This study offers a model-independent understanding of GCR modulation mechanisms.
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