Scholarly Work - Physics

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Microburst Scale Size Derived from Multiple Bounces of a Microburst Simultaneously Observed with the FIREBIRD-II CubeSats
(2018-07) Shumko, Mykhaylo; Sample, John; Johnson, Arlo; Blake, Bern; Crew, Alex; Spence, Harlan; Klumpar, David; Agapitov, Oleksiy; Handley, Matthew
We present the observation of a spatially large microburst with multiple bounces made simultaneously by the FIREBIRD‐II CubeSats on February 2nd, 2015. This is the first observation of a microburst with a subsequent decay made by two co‐orbiting but spatially separated spacecraft. From these unique measurements, we place estimates on the lower bounds of the spatial scales as well as quantify the electron bounce periods. The microburst's lower bound latitudinal scale size was 29 ± 1 km and the longitudinal scale size was 51 ± 1 km in low earth orbit. We mapped these scale sizes to the magnetic equator and found that the radial and azimuthal scale sizes were at least 500 ± 10 km and 530 ± 10 km, respectively. These lower bound equatorial scale sizes are similar to whistler‐mode chorus wave source scale sizes, which supports the hypothesis that microbursts are a product of electron scattering by chorus waves. Lastly, we estimated the bounce periods for 200‐800 keV electrons and found good agreement with four common magnetic field models.
Microburst Scale Size Derived From Multiple Bounces of a Microburst Simultaneously Observed With the FIREBIRD-II CubeSats
(2018-09) Shumko, Mykhaylo; Sample, John; Johnson, Arlo; Blake, Bern; Crew, Alex; Spence, Harlan; Klumpar, David; Agapitov, Oleksiy; Handley, Matthew
We present the observation of a spatially large microburst with multiple bounces made simultaneously by the Focused Investigation of Relativistic Electron Bursts: Intensity, Range, and Dynamics II (FIREBIRD‐II) CubeSats on 2 February 2015. This is the first observation of a microburst with a subsequent decay made by two coorbiting but spatially separated spacecraft. From these unique measurements, we place estimates on the lower bounds of the spatial scales as well as quantify the electron bounce periods. The microburst's lower bound latitudinal scale size was 29 ± 1 km and the longitudinal scale size was 51 ± 1 km in low Earth orbit. We mapped these scale sizes to the magnetic equator and found that the radial and azimuthal scale sizes were at least 500 ± 10 km and 530 ± 10 km, respectively. These lower bound equatorial scale sizes are similar to whistler mode chorus wave source scale sizes, which supports the hypothesis that microbursts are a product of electron scattering by chorus waves. Lastly, we estimated the bounce periods for 200‐ to 800‐keV electrons and found good agreement with four common magnetic field models.
Observations Directly Linking Relativistic Electron Microbursts to Whistler Mode Chorus: Van Allen Probes and FIREBIRD II
(2017-12) Breneman, A. W.; Crew, Alex; Sample, John; Klumpar, David; Johnson, Arlo; Agapitov, Oleksiy; Shumko, Mykhaylo; Turner, D. L.; Santolik, O.; Wygant, John R.; Cattell, C. A.; Thaller, S.; Blake, Bern; Spence, Harlan; Kletzing, C. A.
We present observations that provide the strongest evidence yet that discrete whistler mode chorus packets cause relativistic electron microbursts. On 20 January 2016 near 1944 UT the low Earth orbiting CubeSat Focused Investigations of Relativistic Electron Bursts: Intensity, Range, and Dynamics (FIREBIRD II) observed energetic microbursts (near L = 5.6 and MLT = 10.5) from its lower limit of 220 keV, to 1 MeV. In the outer radiation belt and magnetically conjugate, Van Allen Probe A observed rising-tone, lower band chorus waves with durations and cadences similar to the microbursts. No other waves were observed. This is the first time that chorus and microbursts have been simultaneously observed with a separation smaller than a chorus packet. A majority of the microbursts do not have the energy dispersion expected for trapped electrons bouncing between mirror points. This confirms that the electrons are rapidly (nonlinearly) scattered into the loss cone by a coherent interaction with the large amplitude (up to 900 pT) chorus. Comparison of observed time-averaged microburst flux and estimated total electron drift shell content at L = 5.6 indicate that microbursts may represent a significant source of energetic electron loss in the outer radiation belt.