Unidirectional gradient of galactic cosmic ray intensity at different cut-off rigidities and solar magnetic polarities

Abstract

Energetic charged particles known as Galactic cosmic rays (GCRs) are mostly protons originating from supernova remnants. The solar wind modulates the GCR intensity near-Earth along the solar cycles (SCs) in association with the heliospheric magnetic field (HMF). GCR intensity as observed by the neutron monitor at low, medium, high cut-off rigidities (Pc ) is employed to calculate the South-North (SN) asymmetry of GCR densities (n) of different magnetic polarity states (A) of the HMF. The study covered SCs 22/23, 23/24 and 24/25, during negative and positive states (A < 0 and A > 0). We used the modified correction for secular changes in n to determine the SN asymmetry of n (δnS−N /n) with respect to the heliospheric current sheet (HCS), a wavy structure dividing the northern and southern HMFs. We found anti-correlation of corrected tilt angle of HCS [α] for Earth’s excursions in helio-latitude with the corrected δnS−N/n, particularly during A < 0 epoch (2004-2008) and A > 0 epoch (2015-2019 not 1996-1998). The results indicate that HCS drift is crucial for asymmetric modulation and latitude gradient of GCR in both epochs. The asymmetric latitudinal gradient [G ⊥] shows strong positive correlation to the consistency between the corrected δnS−N/n and for all epochs and Pc .