Search for periodicities in the IMP 8 Charged Particle Measurement Experiment proton fluxes for the energy bands 0.50–0.96 MeV and 190–440 MeV

Abstract

Past studies revealed that the photospheric magnetic field, as well as many solar activity phenomena, undergoes both periodic and quasiperiodic variations on different time scales. Nevertheless, only a few attempts have been made so far to detect corresponding variations in the occurrence frequency of solar energetic particle events. Here we search for periodicities in the proton fluxes, measured in the interplanetary space, on time scales ranging from a few (>6) Bartels rotations (27 days) up to the Schwabe (∼11 years) period. We apply the wavelet technique to the proton fluxes recorded by the Charged Particle Measurement Experiment (CPME) instrument aboard IMP 8 spacecraft, from 1974 to 2001, in the energy bands 0.50–0.96 MeV and 190–440 MeV. The reliability of the obtained results is tested by analyzing the wavelet response to suitable artificial functions. The ∼9.8, ∼3.8, and ∼1.7–2.2 year periods are the most significant found in the interplanetary proton flux. Shorter periods (such as ∼1 year) are detected in some time intervals, but they are not significant in the whole sequence of data.