Neutron monitor measurements as a complement to space measurements of energetic solar particle fluxes

Neutron monitors remain indispensable cosmic ray detectors for primary energies from about 500 MeV to 30 GeV. They respond to variations of the cosmic ray intensity of the near-Earth scape that are no measured by space experiments. The records of the world wide network of standardized neutron monitors, therefore, complement cosmic ray spacecraft measurements. In this review paper we first describe the design of a neutron monitor and its characteristic parameters as a continuous ground-based cosmic ray instrument. We then discuss how the data from the world wide network of neutron monitors are evaluated to determine the energetic solar proton fluxes in near-Earth space during the solar cosmic ray events.

We present, as an example, the solar proton fluxes near Earth during the May 7, 1978 solar cosmic ray event. These fluxes were derived from neutron monitor data and measurements of the cosmic ray telescopes on board IMP-7 and cover the energy range from 50 MeV up to 10 GeV. Finally, we describe the method of analyzing solar neutron events. As an example, we summarize the observations made during the solar flare on June 3, 1982 by the Gamma-Ray-Spectrometer on the Solar Maximum Mission Satellite and the Jung-fraujoch neutron monitor. These measurements were used to determine the directional solar neutron emissivity spectrum of the June 3, 1982 solar neutron event over the energy range from 100 MeV to about 3 GeV.