Temporal and energy behavior of cosmic ray fluxes in the periods of low solar activity

TL;DR

This study analyzes how cosmic ray fluxes vary with energy during low solar activity periods over three solar cycles, revealing a softening of the energy spectrum below 10 GeV during minima.

Contribution

It provides a detailed examination of the energy dependence of cosmic ray modulation across multiple solar cycles, highlighting the softening of the spectrum during minima.

Findings

Soft energy spectrum observed during solar minima below 10 GeV.

Energy dependence of cosmic rays has become softer from mid-1980s onwards.

Record high fluxes during the deep minimum between cycles 23 and 24.

Abstract

Modulation of galactic cosmic ray intensity is governed by several mechanisms including diffusion, convection, adiabatic energy losses and drift. Relative roles of these factors change in the course of an 11-year solar cycle. That can result in the changes in the energy dependence of the 11-year cosmic ray modulation. The minimum between the solar cycles 23 and 24 was extremely deep and long-lasting which led to the record high cosmic ray fluxes low-energy particles dominating. This was a signature of unusually soft energy spectrum of the cosmic rays. In this work we examine the energy dependence of the 11-year modulation during the last three solar cycles and argue that a soft energy spectrum was observed in the minimum of each cycle however only for particles below of energy around 10 GeV. From mid 1980s the energy dependence of cosmic rays became softer from minimum to minimum of solar activity. The work is based on the cosmic ray data of the spacecraft, balloon-borne and the ground-based observations.