Re-Entrant Albedo Proton Fluxes Measured by the PAMELA Experiment

TL;DR

This paper reports precise measurements of albedo proton fluxes above 70 MeV by the PAMELA experiment, classifying them into different trapped and un-trapped populations and analyzing the penumbra region near the geomagnetic cutoff.

Contribution

It provides a detailed classification and characterization of high-energy albedo protons at low Earth orbit, improving understanding of their populations and behaviors.

Findings

Identification of quasi-trapped and un-trapped proton populations.

Detailed analysis of the penumbra region near the geomagnetic cutoff.

Enhanced characterization of high-energy albedo proton fluxes.

Abstract

We present a precise measurement of downward-going albedo proton fluxes for kinetic energy above $\sim$ 70 MeV performed by the PAMELA experiment at an altitude between 350 and 610 km. On the basis of a trajectory tracing simulation, the analyzed protons were classified into quasi-trapped, concentrating in the magnetic equatorial region, and un-trapped spreading over all latitudes, including both short-lived (precipitating) and long-lived (pseudo-trapped) components. In addition, features of the penumbra region around the geomagnetic cutoff were investigated in detail. PAMELA results significantly improve the characterization of the high energy albedo proton populations at low Earth orbits.