Third harmonic of the 27 day periodicity of galactic cosmic rays: Coupling with interplanetary parameters

Abstract

Spectral analysis of neutron monitors and muon telescope daily averages counts shows a significant higher harmonic (∼9 day) of the 27 day variation of galactic cosmic rays (CRs). This quasiperiodicity is also present in the time series of daily averages of the product of interplanetary magnetic field magnitude and the square of solar wind speed (BV2). The wavelet spectrum density of the third harmonic of the 27 day variation of CRs is weakly correlated with the quantity BV2. This result reflects the coupling between galactic CR modulation and interplanetary parameters. Copyright 2011 by the American Geophysical Union.