Authors: Andrew Kuhlman (University of Hawaii at Manoa), Veronica Bindi (University of Hawaii at Manoa), Cristina Consolandi (University of Hawaii at Manoa), Claudio Corti (University of Hawaii at Manoa), Alexandria Holthaus (University of Hawaii at Manoa), Nikolay Nikonov (University of Hawaii at Manoa), Siqi Wang (University of Hawaii at Manoa)

Solar Energetic Particles (SEPs) are particles, mainly protons, which are accelerated during explosive events on the sun like solar flares and Coronal Mass Ejections. Particles inside the Earth’s magnetosphere (especially SEPs) can be a significant radiation hazard for humans and technology in space. To accurately measure the increase in particle flux due to SEP events, a characterization of the geomagnetic cutoff is necessary, especially considering that some SEP events occur during a Forbush Decrease when the galactic cosmic ray flux at Earth decreases significantly. The geomagnetic cutoff determines the rigidity required for a particle to reach a specific location inside the Earth’s Magnetosphere, and therefore, allows one to discriminate between primary particles (including SEPs), which follow trajectories originating from outside the magnetosphere, and secondary/trapped particles, which do not. The value of the geomagnetic cutoff varies significantly with altitude, geomagnetic latitude, and incoming direction. We have developed a method of calculating the geomagnetic cutoff using the proton rate from the Alpha Magnetic Spectrometer (AMS), a particle detector that has been operational on the International Space Station since 2011. Implementing corrections due to the efficiencies of the AMS subdetectors is ongoing; once this procedure is finalized, which will use the AMS proton flux instead of the proton rate, this method of estimating the cutoff will be extremely useful for SEP analysis.