Galactic cosmic ray transport in inner heliosphere: Study with ion chamber and neutron monitor data for 1936–2006

Abstract

Galactic cosmic ray (GCR) solar diurnal variation data recorded by shielded ion chambers at Cheltenham/Fredericksburg (CH-IC) and Yakutsk (Yak-IC) are corrected for diurnal temperature variation in upper atmosphere and used to calculate the ratio α of GCR free paths normal (λ⊥) and parallel (λ||) to mean interplanetary magnetic field (IMF) B for 1936–2006; α is an important parameter in theories for GCR modulations in heliosphere including anisotropies. Also, neutron monitor (NM) data at low latitudes (Huancayo / Haleakala) are analyzed for 1953–2006; they are not affected by temperature variation in upper atmosphere. Calculations assume negligible symmetric latitude GCR density gradient (Gθs) based on observational evidence. Results support Ahluwalia and Modzelewska (2020) inference for global network of NMs and Nagoya vertical muon telescope (NagV-MT) that α depends on polarity of B at Earth orbit. GCR modulation theories quote α values much smaller than those computed by us. Flat heliosphere current sheet (HCS) and Master equations derived by Ahluwalia and Dorman (1997) are used for computing α and study its correlation with solar activity for positive (p) and negative (n) polarity intervals of B at 1 AU; B points outward/ inward from the Sun during p/n interval in northern hemisphere, IMF polarity changes sign near sunspot number (SSN) maximum. The results challenge validity of the conceptual understanding of GCR modulation processes in the heliosphere, pointing to a need for an acceptable theory to explain empirical results reported in this paper. We propose two Ulysses-like spacecrafts be put in a fast scan mode, making complimentary observations in solar north and south hemispheres for at least a complete solar cycle to obtain more precise information about temporal variations of GCR latitude gradients with solar activity and its dependence on GCR rigidity, facilitating a physically meaningful computation of α.