Characteristics of Relativistic Microburst Intensity From SAMPEX Observations

Abstract

Relativistic electron microbursts are an important electron loss process from the radiation belts into the atmosphere. These precipitation events have been shown to significantly impact the radiation belt fluxes and atmospheric chemistry. In this study we address a lack of knowledge about the relativistic microburst intensity using measurements of 21,746 microbursts from the Solar Anomalous Magnetospheric Particle Explorer (SAMPEX). We find that the relativistic microburst intensity increases as we move inward in L, with a higher proportion of low‐intensity microbursts (<2,250 [MeV cm2 sr s]−1) in the 03–11 magnetic local time region. The mean microburst intensity increases by a factor of 1.7 as the geomagnetic activity level increases and the proportion of high‐intensity relativistic microbursts (>2,250 [MeV cm2 sr s]−1) in the 03–11 magnetic local time region increases as geomagnetic activity increases, consistent with changes in the whistler mode chorus wave activity. Comparisons between relativistic microburst properties and trapped fluxes suggest that the microburst intensities are not limited by the trapped flux present alongside the scattering processes. However, microburst activity appears to correspond to the changing trapped flux; more microbursts occur when the trapped fluxes are enhancing, suggesting that microbursts are linked to processes causing the increased trapped fluxes. Finally, modeling of the impact of a published microburst spectra on a flux tube shows that microbursts are capable of depleting <500‐keV electrons within 1 hr and depleting higher‐energy electrons in 1–23 hr.

Statistical Properties of Electron Curtain Precipitation Estimated With AeroCube‐6

“…Lastly, Figure 5b shows that curtains are associated with an enhanced AE up to around 600 nT. While it is not a direct comparison (due to the electron energy channels and the binning scheme), Douma et al (2019) showed that the number of microburst observed by SAMPEX also increases with increasing AE, up to about AE = 300 nT.…”

“…While the impact of curtains on the magnetosphere and Earth's atmosphere is unknown, the impact of microbursts has been estimated to be substantial. Lorentzen, Looper, et al (2001), Thorne et al (2005), Breneman et al (2017), and Douma et al (2019), among others, estimated that microbursts could deplete the outer radiation belt electrons in about a day. Furthermore, Seppälä et al (2018) modeled a 6‐hr microburst storm and concluded that microbursts depleted mesospheric ozone by roughly 10%.…”

Cosmic noise absorption signature of particle precipitation during interplanetary coronal mass ejection sheaths and ejecta

“…More details on the CNA derivation (in particular the determination of the quiet-day curve) from SGO riometer observations can be found in Sect. 2.1.3 of Grandin (2017).…”

Impact of EMIC‐Wave Driven Electron Precipitation on the Radiation Belts and the Atmosphere

“…For this thought‐experiment, however, a constant loss‐rate is sufficient to determine the relative impact of the precipitation at different energies; a very similar approach was undertaken to investigate the long‐term impact of electron microburst precipitation on trapped electron fluxes by Douma et al. (2019).…”

“…We note that Equation 1 is time-invariant-a more realistic approach would be to introduce some time-dependence to better model the decaying trapped flux. For this thought-experiment, however, a constant loss-rate is sufficient to determine the relative impact of the precipitation at different energies; a very similar approach was undertaken to investigate the long-term impact of electron microburst precipitation on trapped electron fluxes by Douma et al (2019). interaction time between electrons and EMIC waves is not exactly clear, as it depends not only on the energy of the electrons in question, but also strongly on the longitudinal extent of the EMIC-wave region, which is in general fairly difficult to determine, and has to date largely only been examined on a case-by-case basis (e.g., Hendry et al, 2020).…”