Astroparticle Physics

1417 Secondary Cosmic Rays“There are more things in heaven and earth,Horatio, than are dreamt of in your philosophy.”Shakespeare, HamletFor the purpose of astroparticle physics the influence of theSun and the Earth’s magnetic field is a perturbation, whichcomplicates a search for the sources of cosmic rays. Thesolar activity produces an additional magnetic field whichprevents part of galactic cosmic rays from reaching Earth.Figure 7.1, however, shows that the influence of the Sunis limited to primary particles with energies below 10 GeV.The flux of low-energy primary cosmic-ray particles is anticorrelatedto the solar activity.solar modulationFig. 7.1Modulation of the primaryspectrum by the 11-year cycle ofthe SunFig. 7.2Flux densities of protons andelectrons in the radiation belts ofthe EarthOn the other hand, the solar wind, whose magnetic fieldmodulates primary cosmic rays, is a particle stream in itself,which can be measured at Earth. The particles constitutingthe solar wind (predominantly protons and electrons) are oflow energy (MeV region). These particles are captured to alarge extent by the Earth’s magnetic field in the Van Allenbelts or they are absorbed in the upper layers of the Earth’satmosphere (see Fig. 7.9). Figure 7.2 shows the flux den-solar wind