segunda-feira, dezembro 04, 2017

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.

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