Abstract
The main objective is to check whether the periodicities observed in the cosmic rays in the interval 2013-2018 are affected by the magnetic rigidity or the height at which the neutron monitors are placed. A Global Neutron Monitor (GNM) has been defined as representative of the neutron monitor global network. The Morlet wave - let analysis is applied to the GNM and the selected solar activity parameters to find out common periodicities. Short-term periodicities of 13.5, 27, 48, 92, 132 and 298 days have been observed in cosmic ray intensity. A clear inverse relationship between rigidity and spectral power has been obtained for the 13.5, 48, 92, 132-day periods. A not so clear but still observed direct relationship between the height of the neutron monitors and the spectral power for the 48, 92, 132-day periods has been also found. The periodicity of 92 days is the one which shows the highest dependence with rigidity cutoff and height. As far as we know, this is the first time that these dependencies are reported. We think that these observations could be explained by assuming some cosmic ray intensity energy dependence in such periodicities and a competitive effect between rigidity and height.
Highlights
The primary cosmic rays are electrically charged high energy particles, mostly originating in violent phenomena of our galaxy and, to a lesser extent, solar or extragalactic phenomena, that continuously affect the terrestrial atmosphere with energies between 106 and 1020 eV/nucleon
The Morlet wavelet analysis is applied to the Global Neutron Monitor (GNM) and the selected solar activity parameters to find out common periodicities
Once the outliers are substituted in the data from the selected stations, the wavelet analysis is applied to their counting rates to find out periodicities in the data
Summary
The primary cosmic rays are electrically charged high energy particles, mostly originating in violent phenomena of our galaxy (such as supernova explosions, pulsars with very strong magnetic fields) and, to a lesser extent, solar or extragalactic phenomena, that continuously affect the terrestrial atmosphere with energies between 106 and 1020 eV/nucleon When these primary CR interact with particles present in the Earth’s atmosphere, other particles called secondary cosmic rays, such as protons, muons, neutrons and mesons are created. To study the solar activity through NMs requires the use of multiple stations located in different geomagnetic locations because their position with respect to the Earth’s magnetic field determines the minimum energy of cosmic rays to generate counts on a given NM This need justifies the foundation of the NMDB. Cosmic Ray Intensity is anticorrelated to the solar activity, measured by the sunspot number, with a certain delay caused by irregularities in the Interplanetary Magnetic Field, Forbush (1958) and Usoskin et al (1998)
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