Cosmic rays: bringing messages from the sky to the Earth's surface

Abstract

All the evolution of the scientific knowledge about Cosmic Rays (CRs) in the 20 t h century leads to the following statement: Cosmic Rays constitutes a time and spatial variable flux of fully ionized energetic atoms and sub-atomic particles with specific abundances and energies that continuously permeates the solar system, reaching the Earth and producing ionization and nuclear reactions in our atmosphere. Since the primary CR flux is composed of charged particles, it is expected that any magnetic irregularity and/or turbulence affects their large scale transport and consequently its energy spectrum. Moreover, since the interaction of the CR particles with the terrestrial atmosphere produces not only atmospheric ionization, but also nuclear reactions (creating a cascade of secondary particles), it is easy to understand that near ground CR measurements (direct or indirect) may allow us to study the physical processes involved in the journey of CR particles (including the birth conditions of the lower energetic ones and the propagation of the higher energetic ones through the heliosphere) before reaching the terrestrial environment, and also along the transport of the secondary particles into the Earth's atmosphere. In this sense, considering a cosmic ray particle as a ”celestial messenger” is reasonable. Therefore, several works have been using the CR footprints found in the terrestrial surface (through the ground-based measurement of cosmogenic tracers) as a tool for solar and atmospheric studies. It is present here a discussion concerning the time evolution of the CR scientific knowledge and a brief review of the physical concepts of those celestial messengers.