Modulation of High-Energy Particles and the Heliospheric Current Sheet Tilts throughout 1976-2014

TL;DR

This study analyzes how cosmic ray intensities are affected by the tilt angles of the heliospheric current sheet over three solar cycles, revealing polarity-dependent sensitivities and hysteresis effects.

Contribution

It provides new insights into the relationship between cosmic ray intensities, heliospheric current sheet tilts, and magnetic field polarity over multiple solar cycles.

Findings

CRIs are sensitive to heliospheric current sheet tilt angles.

Stronger correlation when the North Polar Magnetic Field is inward.

Faster decrease of CRIs with tilt during qA < 0.

Abstract

Cosmic ray intensities (CRIs) recorded by sixteen neutron monitors have been used to study its dependence on the tilt angles (TA) of the heliospheric current sheet (HCS) during period 1976-2014, which covers three solar activity cycles 21, 22 and 23. The median primary rigidity covers the range 16-33 GV. Our results have indicated that the CRIs are directly sensitive to, and organized by, the interplanetary magnetic field (IMF) and its neutral sheet inclinations. The observed differences in the sensitivity of cosmic ray intensity to changes in the neutral sheet tilt angles before and after the reversal of interplanetary magnetic field polarity have been studied. Much stronger intensity-tilt angle correlation was found when the solar magnetic field in the North Polar Region was directed inward than it was outward. The rigidity dependence of sensitivities of cosmic rays differs according to the IMF polarity, for the periods 1981-1988 and 2001-2008 (qA < 0) it was R-1.00 and R-1.48 respectively, while for the 1991-1998 epoch (qA > 0) it was R-1.35. Hysteresis loops between TA and CRIs have been examined during three solar activity cycles 21, 22 and 23. A consider differences in time lags during qA > 0 and qA < 0 polarity states of the heliosphere have been observed. We also found that the cosmic ray intensity decreases at much faster rate with increase of tilt angle during qA < 0 than qA > 0, indicating stronger response to the tilt angle changes during qA < 0. Our results are discussed in the light of 3D modulation models including the gradient, curvature drifts and the tilt of the heliospheric current sheet.