Pecularities of cosmic ray modulation in the solar minimum 23/24

TL;DR

This study analyzes galactic cosmic ray modulation during the solar minimum 23/24, revealing consistent physical mechanisms and modeling cosmic ray transport with increased diffusion coefficients during the period.

Contribution

It presents a 2-D non-stationary transport model of GCRs that accounts for solar cycle variations and demonstrates increased diffusion coefficients during the minimum.

Findings

GCR intensity increased in 2009 due to decreased solar wind and magnetic field strength.

Rigidity dependence of GCR variations remains consistent before and after 2009.

The diffusion coefficient for cosmic rays increased by 30% in 2009 compared to 1996.

Abstract

We study changes of the galactic cosmic ray (GCR) intensity for the ending period of the solar cycle 23 and the beginning of the solar cycle 24 using neutron monitors experimental data. We show that an increase of the GCR intensity in 2009 is generally related with decrease of the solar wind velocity U, the strength B of the interplanetary magnetic field (IMF), and the drift in negative (Aneg) polarity epoch. We present that temporal changes of rigidity dependence of the GCR intensity variation before reaching maximum level in 2009 and after it, do not noticeably differ from each other. The rigidity spectrum of the GCR intensity variations calculated based on neutron monitors data (for rigidities greaten than 10 GV) is hard in the minimum and near minimum epoch. We do not recognize any non-ordinary changes in the physical mechanism of modulation of the GCR intensity in the rigidity range of GCR particles to which neutron monitors respond. We compose 2-D non stationary model of transport equation to describe variations of the GCR intensity for 1996-2012 including the Apos (1996-2001) and the Aneg (2002-2012) periods; diffusion coefficient of cosmic rays for rigidity 10-15 GV is increased by 30 percent in 2009 (Aneg) comparing with 1996 (Apos). We believe that the proposed model is relatively realistic and obtained results are satisfactorily compatible with neutron monitors data.