SOLAR MODULATION OF GALACTIC COSMIC RAYS WITH HELMOD-4

Solar Modulation is a decrease in galactic cosmic rays (GCR) intensity with respect to the Local Interstellar Spectrum (LIS, i.e., the spectra at the border of the heliosphere) typically at energies lower than 30 GeV/Nucl. The intensity varies with time and is anti-correlated with solar activity at these energies. This process is described by Parker’s Equation, a Fokker-Plank-like equation that includes diffusion, convection, and energy loss of GCR propagating within the Heliosphere. Modulated omnidirectional intensities of GCRs were observed during different solar activity phases using both balloon flights and space-borne missions, in particular, during the latest solar cycles. The increased performance of on-board spectrometers was and is currently enabling to enhance the accuracy of the observed spectra. Thus, it was opening the way to a more in-depth understanding of processes related to the transport of GCRs through the Heliosphere and, ultimately, to the capability (a) to unveil LIS of GCR species; (b) to investigate their generation, acceleration, and diffusion process within the Milky Way; (c) to possibly untangle features due to new physics — i.e., dark matter — or additional astrophysical sources so far not considered. HelMod-4 Code was developed to solve the Parker Equation inside the Heliosphere using a Monte Carlo approach. The HelMod-4 model balances complexity with user accessibility. It assesses GCR spectrum variations during different solar phases, with recent updates emphasizing solar cycle 24. This model is valuable for forecasting space radiation environments and understanding CR propagation through the heliosphere. A joint effort between GALPROP and HelMod-4 codes combines CR source and propagation models with solar modulation effects, allowing us to infer LISs and, by comparison with experimental data, to exploit structures and unexpected excess in the GCR spectra. A summary of relevant results from this joint effort is then presented and discussed.