  The fluxes of atmospheric muons and neutrinos are calculated by a three
dimensional Monte Carlo simulation with the air shower code CORSIKA using the
hadronic interaction models DPMJET, VENUS, GHEISHA, and UrQMD. For the
simulation of low energy primary particles the original CORSIKA has been
extended by a parametrization of the solar modulation and a microscopic
calculation of the directional dependence of the geomagnetic cut-off functions.
An accurate description for the geography of the Earth has been included by a
digital elevation model, tables for the local magnetic field in the atmosphere,
and various atmospheric models for different geographic latitudes and annual
seasons. CORSIKA is used to calculate atmospheric muon fluxes for different
locations and the neutrino fluxes for Kamioka. The results of CORSIKA for the
muon fluxes are verified by an extensive comparison with recent measurements.
The obtained neutrino fluxes are compared with other calculations and the
influence of the hadronic interaction model, the geomagnetic cut-off and the
local magnetic field on the neutrino fluxes is investigated.
