Seminar: Energetic particle injections and Earth’s radiation belt electrons
Wednesday, November 10, 2021 - 3:00pm to 4:00pm
Speaker Drew Turner, a postdoctoral researcher at UNH, will discuss energetic particle injections and Earth’s radiation belt electrons: Critical ties between the magnetotail and inner magnetosphere.
In this talk, I’ll focus on the critical role that energetic particle injections from Earth’s magnetotail plasma sheet play in driving the extreme and chaotic variability of relativistic (≥100 keV) electrons in Earth’s radiation belts. Energetic particle injections are thought to occur due to accelerated particles in the plasma sheet (10s to 100s keV) drift-resonating with, or even being quasi-stably trapped by, fast (100s km/s), mesoscale (1000s km to ~3 RE) plasma flows moving earthward from active reconnection sites. However, some challenges remain as to whether that picture can explain all energetic particle injections, or if there are different types depending on level of substorm activity. Once injected into the inner magnetosphere, energetic electrons contribute to the growth of whistler-mode chorus waves and also provide a “seed” population of several 100 keV electrons that can resonate with and be rapidly accelerated by those same chorus waves. This mechanism is thought to be responsible as the source of relativistic electrons in the outer radiation belt during sudden enhancement events. Furthermore, there is a noted relationship between energetic particle injections, substorm activity, and sudden particle enhancements at low L-shells (SPELLS; down to L < 3). We will briefly discuss the latest insights on SPELLS revealed by Van Allen Probes and show evidence that these events are the dominant source of 100s of keV to ~1.5 MeV electrons in the inner radiation belt. Finally, we will return to the plasma sheet and investigate two interesting aspects of energetic electron injections: 1) whether the source of electrons in the plasma sheet might ever serve as a direct source of MeV electrons in the outer radiation belt, and 2) why injections of >300 keV electrons into and inside of GEO (~6.6 RE geocentric distance) are extremely rare. Using new results from MMS and Van Allen Probes, we will show that there is often significant source of ~MeV electrons in the plasma sheet, yet those rarely are injected into the outer belt. We finish with a discussion of the mystery surrounding what might be so efficiently accelerating electrons to such high energies in the plasma sheet and some thoughts for future mission architectures to study these interesting physics of relativistic electron acceleration in magnetospheric systems.