Time dependence of the proton flux measured by PAMELA during the July 2006 - December 2009 solar minimum

TL;DR

This study analyzes how solar activity during a prolonged solar minimum affected galactic proton flux near Earth, using PAMELA data from 2006 to 2009, and compares observations with advanced solar modulation models.

Contribution

It provides detailed, time-resolved measurements of proton spectra during a unique solar minimum and compares them with a sophisticated 3D solar modulation model.

Findings

Proton flux varied significantly over the period.

Data closely match the 3D solar modulation model.

Proton spectra showed clear solar cycle dependence.

Abstract

The energy spectra of galactic cosmic rays carry fundamental information regarding their origin and propagation. These spectra, when measured near Earth, are significantly affected by the solar magnetic field. A comprehensive description of the cosmic radiation must therefore include the transport and modulation of cosmic rays inside the heliosphere. During the end of the last decade the Sun underwent a peculiarly long quiet phase well suited to study modulation processes. In this paper we present proton spectra measured from July 2006 to December 2009 by PAMELA. The large collected statistics of protons allowed the time variation to be followed on a nearly monthly basis down to 400 MV. Data are compared with a state-of-the-art three-dimensional model of solar modulation.