Study of solar modulation effects on cosmic ray fluxes measured by the AMS experiment

As cosmic rays traverse through the solar system they are faced with an outward flow of highly-conductive magnetised plasma known as the Solar Wind. Embedded in this wind is the turbulent Heliospheric Magnetic Field with which cosmic rays interact, significantly changing both their energy and trajectory. Due to solar activity, the heliosphere is subjected to both short and long-term changes which reflect as temporal variations on the cosmic-ray flux, specially at lower energies (up to 50 GeV). These temporal variations of cosmic ray intensity in the heliosphere are known as the Solar Modulation of Galactic Cosmic Rays. AMS-02, the Alpha Magnetic Spectrometer is a high-precision state-of-the-art cosmic-ray detector installed in the International Space Station, continuously monitoring the cosmic-ray flux as it changes with time positioning it as a unique platform to study Solar Modulation. In this thesis we will begin by briefly exploring the history of the discovery of cosmic rays and showcase AMS as the detector used to observe them. After, we characterise the estimation of a cosmic-ray flux in detail as we study the performance of the different AMS detectors involved. Finally we describe the process by which we use AMS’ high-precision detectors to identify the cosmic-ray particles arriving at the detector and how we estimated the 27-day (known as Bartel solar rotation) time-resolved cosmic-ray proton flux. We will then introduce the physical process that is Solar Modulation and present an over- view of Parker’s transport equation and its connections to the solar magnetic field through the different propagation parameters. Utilising modern frequency-analysis techniques we characterised the time-resolved pro- ton flux, in both time and frequency domains, as we correlated it to the different temporal periodicities present in the Solar Activity Cycle. Using a data-driven model of cosmic-ray transport in the heliosphere, in combination with a large collection of data, we showed evidence of an eight-month time-lag between observations of solar activity and measurements of cosmic-ray fluxes in space. This result enables us to forecast the cosmic ray flux on Earth well in advance by monitoring solar activity.