EAGER: On the Impact of Solar Energetic Particles in the High Latitude Regions

Solar energetic particles (SEPs) from the Sun can penetrate Earth’s magnetic environment, disturb the upper atmosphere, and disrupt high-frequency radio communications used in aviation, emergency response, scientific operations, and national security. This project will analyze unique measurements from more than a dozen SEP events over Earth’s polar regions to investigate how Earth’s magnetic field regulates SEP access to the atmosphere and whether energetic electrons play a previously underappreciated role in polar cap absorption events. The study builds upon an NSF-supported CubeSat mission and will establish the scientific and analysis framework needed for an upcoming NSF-supported instrument on the interplanetary space mission to the asteroid belt. By combining satellite and ground-based observations, the project will explore new ideas about Sun–Earth interactions and improve understanding of how space weather affects the near-Earth space environment. All resulting data products and analysis tools will be made publicly available to enable broad community use and to stimulate further exploratory research. The project will support the training of graduate students in space physics data analysis and multi-platform observations. The Relativistic Electron and Proton Telescope integrated little experiment (REPTile) onboard the NSF-funded Colorado Student Space Weather Experiment (CSSWE) CubeSat demonstrated that a student-led CubeSat mission can deliver transformative science through the discovery of Cosmic Ray Albedo Neutron Decay (CRAND) electrons in the inner radiation belt. Building on this heritage, REPTile-2 flew on a NASA CubeSat mission (Apr 2023–Oct 2024) in a highly inclined low-Earth orbit, providing high-energy-resolution measurements of energetic protons and electrons. During its 1.5-year operation, REPTile-2 recorded more than 12 solar energetic particle (SEP) events over Earth’s high-latitude regions. This project will conduct an exploratory analysis of REPTile-2 SEP observations in conjunction with concurrent NOAA/POES, MetOp, and ground-based riometer measurements. It will quantify storm-time variability of cutoff latitudes, characterize energy-dependent SEP access, and examine relationships among SEP spectra, geomagnetic conditions, magnetic local time, and ionospheric absorption. The project will provide new insight into particle transport, magnetosphere–ionosphere coupling, and storm-time geospace dynamics, while establishing the analysis framework needed for analyzing future REPTile-3 measurements. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria. NSF Award ID: 2618143 | Program: 01002627DB NSF RESEARCH & RELATED ACTIVIT | Principal Investigator: Xinlin Li | Institution: University of Colorado at Boulder, BOULDER, CO | Award Amount: $299,673 View on NSF Award Search: https://www.nsf.gov/awardsearch/show-award/?AWD_ID=2618143 View on Research.gov: https://www.research.gov/awardapi-service/v1/awards/2618143.html