Observation of an Electron Microburst With an Inverse Time‐Of‐Flight Energy Dispersion

• Published in: Geophysical research letters 2023-08, Vol.50 (15), p.n/a
• Main Authors: Shumko, M., Miyoshi, Y., Blum, L. W., Halford, A. J., Breneman, A. W., Johnson, A. T., Sample, J. G., Klumpar, D. M., Spence, H. E.
• Format: Article
• Language: English
• Subjects: Acceleration; Aerospace environments; Atmospheric models; Balloons; chorus wave; Chorus waves; CubeSat; Cyclotron resonance; Dispersion; Earth; Earth orbits; Electron microbursts; Electron precipitation; Electrons; Energy; FIREBIRD; Flight; Gyrofrequency; High altitude; High altitude balloons; Kinetic energy; Low earth orbits; Meteorological balloons; microburst; Microbursts; Microbursts (meteorology); Narrowband; Outer radiation belt; Particle acceleration; Particle interactions; Plasma waves; Precipitation; Radiation; Radiation belt electrons; Radiation belts; Resonance; Resonance scattering; Time dependence
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2023GL104804

Interactions between whistler mode chorus waves and electrons are a dominant mechanism for particle acceleration and loss in the outer radiation belt. One form of this loss is electron microburst precipitation: a sub‐second intense burst of electrons. Despite previous investigations, details regarding the microburst‐chorus scattering mechanism—such as dominant resonance harmonic—are largely unconstrained. One way to observationally probe this is via the time‐of‐flight energy dispersion. If a single cyclotron resonance is dominant, then higher energy electrons will resonate at higher magnetic latitudes: sometimes resulting in an inverse time‐of‐flight dispersion with lower‐energy electrons leading. Here we present a clear example of this phenomena, observed by a FIREBIRD‐II CubeSat on 27 August 2015, that shows good agreement with the Miyoshi‐Saito time‐of‐flight model. When constrained by this observation, the Miyoshi‐Saito model predicts that a relatively narrowband chorus wave with a ∼0.2 of the equatorial electron gyrofrequency scattered the microburst. Plain Language Summary Wave‐particle interactions are a ubiquitous phenomenon in plasmas. Around Earth, interactions between electrons and a plasma wave termed whistler mode chorus leads to both the acceleration of the outer Van Allen radiation belt electrons, and rapid precipitation of electrons into Earth's atmosphere. One form of this precipitation is called electron microbursts: a sub‐second and intense bursts of electrons most often observed by high altitude balloons and low Earth orbiting satellites. While microbursts have been studied since the dawn of the Space Age, fundamental details regarding how they are generated are largely unknown. One clue to the properties of the scattering mechanism comes from energy‐dependent time‐of‐flight dispersion signatures. Electrons with a larger kinetic energy move faster, and will therefore precipitate before the electrons with lower kinetic energy. However, in this paper we show observations made by the FIREBIRD‐II CubeSat mission of the opposite: lower‐energy electrons arriving first. This counter‐intuitive phenomena, termed inverse time‐of‐flight energy dispersion, together with models, is a powerful tool to sense the detailed nature of how plasma waves scatter electrons in Earth's near space environment. Key Points FIREBIRD‐II observed a microburst whose 250 keV electrons arrived before the 650 keV electrons We estimate that the observed inverse energy dis