Ground-Based Measurements of Energetic Particles by Neutron Monitors

Abstract

Since the International Geophysical Year (IGY) in 1957/58, the worldwide network of neutron monitors is the standard instrument to investigate the variations of the cosmic ray flux near Earth (11-year modulation of the galactic cosmic rays, Forbush decreases, solar cosmic ray events) in the GeV range. The ensemble of neutron monitors together with the geomagnetic field acts as a giant spectrometer and enables to deduce information about the primary cosmic ray spectrum near Earth in the energy range ∼ 500 MeV to ∼ 15 GeV. For the interpretation of the ground-based neutron monitor measurements, the transport of the cosmic rays in the Earth’s magnetic field as well as the transport in the Earth’s atmosphere and the detection efficiency of the secondary nucleons by the neutron monitors must be known. The Neutron Monitor Data Base (NMDB) developed in 2008/09 enables a rapid accessibility to the data of the worldwide neutron monitor network. A considerable number of neutron monitor stations send their data to NMDB in real-time which enables the operation of space weather applications based on neutron monitor data.