GEM: From the Micro to the Macro--Identifying the Mechanisms Responsible for Megaelectron-Volt (MeV) Electron Microbursts and Quantifying Their Role in Global Radiation Belt Losses

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The dynamical evolution of the Earth’s radiation belts is governed by the relative balance between particles being accelerated and transported into and lost from the magnetosphere. Relativistic electron microbursts are one source of particle losses in the magnetosphere. This work is a modeling effort to better understand the physical process of losses from microbursts. The work will have a broader impact on the technological infrastructure that supports our society and national security, due to the significant space weather hazard that radiation belt electrons pose to Earth-orbiting spacecraft. Two undergraduates and one graduate student researcher will be supported.The effort will develop a computational framework to identify the physical mechanisms that produce relativistic electron microbursts in the Earth’s outer radiation belt and to quantify, for the first time, accurate loss estimates due to this scattering process. The science investigation will be carried out as follows. Numerical ray tracing will be used to calculate the chorus wave power spectrum (frequency and wave normal angle) as a function of time and location along a given magnetic field line, including Landau damping. Then, the wave power distribution will be used to calculate the resultant pitch-angle change near the loss cone at each point along the field line due to resonant interactions with the obtained chorus wave field, including nonlinear effects. This is then repeated for a set of test-particles (i.e., energetic electrons) over a range of initial energies. For an assumed radiation belt electron distribution taken from an empirical model, the work calculates the spatio-temporal dependence of the electron flux precipitated into the ionosphere due to the derived resonant pitch-angle scattering. Repeating this entire procedure across a range of locations provides a map of the electron flux precipitated into the ionosphere as a function of time, position, and energy, due to resonant interactions with chorus waves. With these model calculations in hand, the work explores and evaluates the various potential mechanisms involved in the scattering through parameter variation, for example by increasing/suppressing Landau damping, or by restricting/including higher order resonances. These mechanisms will then be additionally scrutinized through data-model comparisons, both statistical and for an individual event.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.