Rapid sub-second relativistic electron precipitation, termed microbursts, has long been associated with whistler mode chorus wave activity. The similar distributions in local time and l shell…

This is a $681,457 grant awarded by the NASA Shared Services Center to the Regents of the University of Colorado, performing work at its Boulder, Colorado campus. The grant will fund research to investigate the characteristics and generation mechanisms of relativistic electron microbursts, a type of rapid precipitation of high-energy electrons from the Earth's radiation belts. The research will combine data analysis from satellites, modeling of chorus wave-particle interactions, and test particle simulations to better understand the key factors controlling microburst properties. This work is directly relevant to NASA's Heliophysics Division goals, including improving understanding of magnetosphere-ionosphere-atmosphere coupling and fundamental plasma processes within the heliosphere. The grant does not have a set-aside designation.

Rapid sub-second relativistic electron precipitation, termed microbursts, has long been associated with whistler mode chorus wave activity. The similar distributions in local time and l shell between the waves and precipitation features suggest that the two phenomena are likely related, and theoretical calculations have shown that chorus waves can rapidly scatter energetic electrons through nonlinear interactions. While the occurrence rates and magnitudes of relativistic microbursts have been studied by previous authors, there has been little attention to the more detailed properties of these phenomena, which can give further insight into their generation. Through a combination of data analysis, RAY tracing, and test particle simulations, we propose to explore what key chorus wave properties (e.g. frequency extent, sweep rate, wave amplitude, latitude of interaction) control microburst characteristics (e.g. burst duration, pitch angle anisotropy, energy dependence) and how are these are mediated by wave-particle interaction physics. Specifically, we aim to answer the following science questions: 1. What are the characteristics of relativistic electron microbursts? 2. How are relativistic electron microbursts produced? 3. What wave and plasma characteristics dictate the precipitation properties? To address these questions, we will utilize a combination of data analysis, including microburst measurements by satellites in low- earth orbit (LEO) and chorus wave measurements near the equatorial plane, as well as test particle simulations to study chorus wave electron interactions. We propose to perform the following tasks: 1. Analyze microburst properties in the sampex and firebird II datasets, including burst duration, energy dependence, and pitch angle anisotropy 2. Analyze chorus wave properties in van allen probe data, including frequency extent, sweep rate, and wave amplitude 3. Perform test particle simulations to model chorus wave-electron interactions and examine key magnetospheric parameters that control microburst precipitation properties through data-model comparisons, we will explore the correspondence between measured and simulated microburst properties, relating both individual burst characteristics as well as their global dependencies to chorus wave parameters. Relevance to NASA: the proposed work is directly relevant to the goals and objectives of NASA s heliophysics division and addresses two of the four heliophysics decadal survey goals, determining the dynamics and coupling of earth s magnetosphere, ionosphere, and atmosphere and their response to solar and terrestrial inputs and discovering and characterizing fundamental processes that occur both within the heliosphere and throughout the universe. Wave-particle interactions are ubiquitous throughout the heliosphere and have important implications for particle energization as well as scattering. As energetic electron precipitation is a critical process both for radiation belt dynamics in earth s magnetosphere as well as for energy input to earth s atmosphere, the results of this effort will have important cross-disciplinary implications.