Sketch of the altitude-dependent evolution of a secondary particle cascade induced by a high-energy primary cosmic ray particle (Z = 1–28). The cascade develops three branches: the electromagnetic branch mainly consisting of electrons, positrons and photons (also known as “soft component”), the muonic branch (the “hard component”), as well as the hadronic branch, mainly consisting of neutrons and protons (see, e.g., Bazilevskaya et al. 2008).