Solar activity varies strongly with time (approximately over 11 years) from a minimum level, when the Sun is quiet, to a maximum of activity. Cosmic rays of galactic origin respond to this activity, that significantly modifies the original differential spectra depending on particle energy, species, sign of charge and time, when measured at Earth. The resulting solar modulation effect is evident in neutron monitor data, showing a clear anticorrelation between particle intensities and solar activity. Particles with rigidities up to at least 30 GV are mainly affected and the effect becomes progressively larger as the rigidity decreases.
Solar activity is characterized by a number of transient phenomena such as solar flares - sudden flashes of particles observed on the Sun’s surface - and Coronal Mass Ejections, when a huge amount of matter and magnetic field is emitted. The ejected particles can be accelerated at an energy ranging from a few tens of keV to a few GeV (Solar energetic particles - SEP) and escape the Sun magnetic field; transported through the heliosphere they can reach the Earth causing geomagnetic storms by interacting with the outermost layers of the magnetosphere.
CSES mission will monitor the solar impulsive activity and cosmic ray solar modulation, by detecting proton and electron fluxes from a few MeV to hundreds of MeV. The measurements will provide an extension up to very low energy of the range of the particle spectra that are monitored, in the current 24th solar cycle, by PAMELA and AMS experiments. It will be also possible to compare the measured spectra with those from other space mission, such as GOES and ACE.
Solar Modulation of Galactic Cosmic Rays
Proton fluxes vs energy - Solar Flare December 13th, 2006