Solar modulation of the galactic cosmic ray spectra since the maunder minimum

Abstract

Investigations on the galactic cosmic ray (GCR) flux in the past centuries are important for understanding the heliospheric modulation effects during prolonged solar quiet periods like the Gleissberg minima and the Maunder minimum of solar activity. We inferred the GCR annual mean spectra on the basis of the following data: primary spectra of cosmic rays obtained from balloon and spacecraft measurements during different phases of the solar cycles # 20-23; the Climax neutron monitor time series available since 1953; variation of the annual means of the coronal source magnetic flux as derived from the aa index available since 1868 and of the evolution of the Sun's large scale magnetic field; the sunspot number time series from 1600. The differential flux of the galactic cosmic ray JG(T,M) (particles/m2 s sr MeV) has been characterized by the parameter M (MeV), the energy lost by particles in traversing the heliosphere, which depends on the modulation by the solar magnetic field. The relations among these data sets were extrapolated back to 1700.