ABSTRACT
Atmospheric neutrinos are produced in meson and muon decays, created by interactions of cosmic rays within the atmosphere. The study of these neutrinos revealed evidence for neutrino oscillations. The part of the cosmic-ray spectrum which is dominantly responsible for the atmospheric neutrino investigations is in the energy range below 1 TeV. In the GeV energy range several effects can occur. This chapter shows a compilation of various measured atmospheric neutrino fluxes. As the atmospheric neutrino results are known, the experiments could be located with a certain distance from the source to cover at least a tiny fraction of the earth diameter and thus a signal. This led to the concept of long-baseline experiments where the source and detectors are more than 100 km away from each other. The first of the accelerator-based long-baseline experiments was the KEK-E362 experiment sending a neutrino beam from KEK to Super-Kamiokande.
