Cosmic Rays in the Heliosphere

Monica Laurenza, INAF-National Institute for Astrophysics, Rome, Italy

Galactic cosmic rays (GCRs) are high-energy protons and atomic nuclei entering the Heliosphere from the interstellar medium and propagating through a turbulent solar wind with an embedded heliospheric magnetic field. This leads to the so-called solar modulation, namely significant global and temporal variations in the GCR intensity and energy spectra as a function of position inside the heliosphere on long time scales (11-year solar activity cycle, 22-year magnetic polarity cycle). The modulation of GCRs involves several physical mechanisms such as diffusion, convection, adiabatic energy losses and drifts. The GCR intensity is also variable at short-term temporal scales. For instance, the large-scale magnetic field configuration of interplanetary perturbations can produce GCR depressions called Forbush decreases. In addition, the emission at the Sun of high-energy solar particles (the so-called solar cosmic rays) produces increases in the GCR intensity. This tutorial provides an overview of GCR variability as measured by the ground-based neutron monitors and spacecraft at different locations in the Heliosphere as well as the physical processes responsible for the solar modulation and short-term variations.