PAMELA's measurements of geomagnetic cutoff variations during the 14 December 2006 storm

TL;DR

This study used PAMELA satellite data to measure how geomagnetic cutoff latitudes for high-energy protons varied during the December 2006 storm, revealing significant reductions linked to magnetospheric changes.

Contribution

First direct measurements of geomagnetic cutoffs for protons in the sub-GeV and GeV range during a major geomagnetic storm.

Findings

Maximum cutoff latitude suppression of about 7 degrees during the storm

Significant correlation between cutoff variations and magnetospheric parameters

First direct measurement of high-energy proton cutoff variations during a geomagnetic storm

Abstract

Data from the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) satellite experiment were used to measure the geomagnetic cutoff for high-energy (>80 MeV) protons during the 14 December 2006 geomagnetic storm. The variations of the cutoff latitude as a function of rigidity were studied on relatively short timescales, corresponding to spacecraft orbital periods (94 min). Estimated cutoff values were compared with those obtained by means of a trajectory tracing approach based on a dynamical empirical modeling of the Earth's magnetosphere. We found significant variations in the cutoff latitude, with a maximum suppression of about 7 deg at lowest rigidities during the main phase of the storm. The observed reduction in the geomagnetic shielding and its temporal evolution were related to the changes in the magnetospheric configuration, investigating the role of interplanetary magnetic field, solar wind and geomagnetic parameters. PAMELA's results represent the first direct measurement of geomagnetic cutoffs for protons with kinetic energies in the sub-GeV and GeV region.