Solar-cycle Variations of South Atlantic Anomaly Proton Intensities Measured with the PAMELA Mission

Abstract

We present a study of the solar-cycle variations of >80 MeV proton flux intensities in the lower edge of the inner radiation belt, based on the measurements of the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) mission. The analyzed data sample covers an ∼8 yr interval from 2006 July to 2014 September, thus spanning from the decaying phase of the 23rd solar cycle to the maximum of the 24th cycle. We explored the intensity temporal variations as a function of drift shell and proton energy, also providing an explicit investigation of the solar modulation effects at different equatorial pitch angles. PAMELA observations offer new important constraints for the modeling of low-altitude particle radiation environment at the highest trapping energies.

The Relativistic Proton Spectrometer: A Review of Sensor Performance, Applications, and Science

“… 2000 ) and the approximately first four years of the PAMELA investigation on the Resurs-DK1 mission (Bruno et al. 2021 ).…”

“…Berthoud et al 2022) yet have not been as thoroughly explored from LEO because of short orbital lifetimes. Some example missions that probed the inner belt below 400 km were the AMS-01 spectrometer on board a space shuttle flight in 1998 (Alcaraz et al 2000) and the approximately first four years of the PAMELA investigation on the Resurs-DK1 mission (Bruno et al 2021).…”

Proton Flux Variations During Solar Energetic Particle Events, Minimum and Maximum Solar Activity, and Splitting of the Proton Belt in the South Atlantic Anomaly

“…In addition to secular drifts, the inner belt particles are affected by solar cycle variation. In fact, the low‐altitude geomagnetically trapped population is known to be coupled to the atmospheric density through changes induced by solar activity (Anderson et al., 2018; Bruno et al., 2021b). Protons with energies above a few tens of MeV mostly originate through the Cosmic‐Ray Albedo Neutron Decay (CRAND) mechanism.…”

“…Hence the SAA has been drifting and growing in recent years (Amit et al, 2021;Anderson et al, 2018;Stassinopoulos et al, 2015), and those secular trends have an effect on the inner belt, especially as observed at Low Earth Orbit (LEO) (Girgis et al, 2021).In addition to secular drifts, the inner belt particles are affected by solar cycle variation. In fact, the low-altitude geomagnetically trapped population is known to be coupled to the atmospheric density through changes induced by solar activity (Anderson et al, 2018;Bruno et al, 2021b). Protons with energies above a few tens of MeV mostly originate through the Cosmic-Ray Albedo Neutron Decay (CRAND) mechanism.…”

Gleissberg Cycle Dependence of Inner Zone Proton Flux

“…The proton flux in the inner zone is anticorrelated with solar activity (Bruno et al., 2021; Dragt, 1971; Huston et al., 1998; Kuznetsov et al., 2010; Li et al., 2020; Lin et al., 2020; Nakano & Heckman, 1968; Qin et al., 2014). During solar maximum, the upper atmosphere is heated and expands due to increased solar EUV (Gombosi, 1998), thus the density at Low Earth Orbit (<1,000 km) increases as the atmospheric scale height increases, and protons encounter higher neutral density along their trajectories.…”