Evidence for a Time Lag in Solar Modulation of Galactic Cosmic Rays
Nicola Tomassetti1, Miguel Orcinha2, Fernando Barão2, and Bruna Bertucci1
Published 2017 November 8 • © 2017. The American Astronomical Society.
The Astrophysical Journal Letters, Volume 849, Number 2
Source/Fonte: AAS NOVA
Artist’s impression of the shower of particles caused when a cosmic ray, a charged particle often produced by a distant astrophysical source, hits Earth’s upper atmosphere. [J. Yang/NSF]
Abstract
The solar modulation effect of cosmic rays in the heliosphere is an energy-, time-, and particle-dependent phenomenon that arises from a combination of basic particle transport processes such as diffusion, convection, adiabatic cooling, and drift motion. Making use of a large collection of time-resolved cosmic-ray data from recent space missions, we construct a simple predictive model of solar modulation that depends on direct solar-physics inputs: the number of solar sunspots and the tilt angle of the heliospheric current sheet. Under this framework, we present calculations of cosmic-ray proton spectra, positron/electron and antiproton/proton ratios, and their time dependence in connection with the evolving solar activity. We report evidence for a time lag ${\rm{\Delta }}T=8.1\pm \,1.2$ months, between solar-activity data and cosmic-ray flux measurements in space, which reflects the dynamics of the formation of the modulation region. This result enables us to forecast the cosmic-ray flux near Earth well in advance by monitoring solar activity.
Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
FREE PDF GRATIS: The Astrophysical Journal Letters
