Collaborative Research: GEM--Plasmapause Control of Outer Radiation Belt Electron Enhancements

About This Grant

The radiation belts are a region of high-energy particles that orbit around the Earth. These energetic particles present a hazard to human exploration and technology in space, especially for satellites in geostationary orbit. Understanding the timing and dominant mechanism of radiation belt enhancement events (sudden, system-wide energization of radiation belt particles) is critical to nation security. This project will determine how the plasmapause (the outer boundary of a region of cold, dense plasma surrounding the Earth) controls radiation belt enhancements. One major acceleration mechanism of radiation belt particles (local acceleration) is driven by plasma waves that only occur outside the plasmapause, so we expect that the radiation belt enhancements that are driven by local acceleration would occur outside the plasmapause while other acceleration mechanisms may drive enhancements inside the plasmasphere. This study will systematically evaluate the long-term behavior of radiation belt enhancements and conduct in-depth case studies to evaluate how plasmapause controls radiation belt enhancement events. Radiation belt enhancement events occur when electrons in near-Earth space are accelerated close to the speed of light. Local acceleration is a major acceleration mechanism, which occurs when 10’s – 100’s keV electrons interact with chorus waves, resulting in particle energization to multiple MeV. Chorus waves can only happen outside the plasmapause, so radiation belt enhancements tend to occur outside the plasmasphere. This study will use multi-spacecraft observations provided by the Global Positioning System (GPS) constellation to study the control of the plasmapause on radiation belt enhancements on timescales over a solar cycle. We will study data from 2008 (when 8 GPS with combined X-ray dosimeters, CXDs, were active) until 2023 (25 active GPS with CXD) and combine these data with plasmapause models to statistically analyze the offset of enhancement locations from the plasmapause and energy-dependence of radiation belt enhancements. Case studies will then be performed to examine why the radiation belt enhancements tend to be offset from the plasmapause, determine the spatial extent of the region of electron energization, and evaluate why some radiation belt enhancements occur inside the plasmasphere. 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.