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Abstract Precipitation of relativistic electrons into the Earth's atmosphere regulates the outer radiation belt fluxes and contributes to magnetosphere‐atmosphere coupling. One of the main drivers of such precipitation is electron scattering by whistler‐mode waves. Such waves typically originate at the equator, where they can resonate with and scatter sub‐relativistic (tens to a few hundred keV) electrons. However, they can occasionally propagate far away from the equator along field lines, reaching middle latitudes, where they can resonate with and scatter relativistic (>500 keV) electrons. Such a propagation is typical for the dayside, but statistically has not been found on the nightside where the waves are quickly damped along their propagation due to Landau damping. Here we explore two events of relativistic electron precipitation from low‐altitude observations on the nightside. Combining measurements of whistler‐mode waves from ground observatories, relativistic electron precipitation from low‐altitude satellites, total electron content maps from GPS receivers, and magnetic field and electron flux from equatorial satellites, we show wave ducting by plasma density gradients is the possible channel that allows the waves to reach middle latitudes and scatter relativistic electrons. We suggest that both whistler‐mode wave generation and ducting can be driven by equatorial mesoscale (with spatial scales of about one Earth radius) transient structures during nightside injections. We also compare these nightside events with observations of ducted waves and relativistic electron precipitation at the dayside, where wave generation and ducting are driven by ultra‐low‐frequency waves. This study demonstrates the potential importance of mesoscale transients in relativistic electron precipitation, but does not however unequivocally establish that ducted whistler‐mode waves are the primary cause of the observed electron precipitation.
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Ionospheric Plasma Density Gradients Associated With Night‐Side Energetic Electron Precipitation
Abstract Energetic electron precipitation from the equatorial magnetosphere into the atmosphere plays an important role in magnetosphere‐ionosphere coupling: precipitating electrons alter ionospheric properties, whereas ionospheric outflows modify equatorial plasma conditions affecting electromagnetic wave generation and energetic electron scattering. However, ionospheric measurements cannot be directly related to wave and energetic electron properties measured by high‐altitude, near‐equatorial spacecraft, due to large mapping uncertainties. We aim to resolve this by projecting low‐altitude measurements of energetic electron precipitation by ELFIN CubeSats onto total electron content (TEC) maps serving as a proxy for ionospheric density structures. We examine three types of precipitation on the nightside: precipitation of <200 keV electrons in the plasma sheet, bursty precipitation of <500 keV electrons by whistler‐mode waves, and relativistic (>500 keV) electron precipitation by EMIC waves. All three types of precipitation show distinct features in TEC horizontal gradients, and we discuss possible implications of these features.
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- PAR ID:
- 10495002
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 50
- Issue:
- 21
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1029/2023GL105630
