Global-scale coherence modulation of radiation-belt electron loss from plasmaspheric hiss

Abstract

Over 40 years ago it was suggested that electron loss in the region of the radiation belts that overlaps with the region of high plasma density called the plasmasphere, within four to five Earth radii, arises largely from interaction with an electromagnetic plasma wave called plasmaspheric hiss. This interaction strongly influences the evolution of the radiation belts during a geomagnetic storm, and over the course of many hours to days helps to return the radiation-belt structure to its 'quiet' pre-storm configuration. Observations have shown that the long-term electron-loss rate is consistent with this theory but the temporal and spatial dynamics of the loss process remain to be directly verified. Here we report simultaneous measurements of structured radiation-belt electron losses and the hiss phenomenon that causes the losses. Losses were observed in the form of bremsstrahlung X-rays generated by hiss-scattered electrons colliding with the Earth's atmosphere after removal from the radiation belts. Our results show that changes of up to an order of magnitude in the dynamics of electron loss arising from hiss occur on timescales as short as one to twenty minutes, in association with modulations in plasma density and magnetic field. Furthermore, these loss dynamics are coherent with hiss dynamics on spatial scales comparable to the size of the plasmasphere. This nearly global-scale coherence was not predicted and may affect the short-term evolution of the radiation belts during active times.

Modulation of chorus intensity by ULF waves deep in the inner magnetosphere

“…Breneman et al [2015] present an event of plasmaspheric hiss modulated by ULF waves over a global scale, leading to modulated electron precipitation. Beside chorus waves, there are also other types of whistler-mode waves, such as plasmaspheric hiss or magnetosonic waves.…”

Rapid Loss of Radiation Belt Relativistic Electrons by EMIC Waves

“…There have been two main competing paradigms for the loss of radiation belt relativistic electrons: radial loss to the magnetopause (Shprits, Thorne, Friedel, et al, ; Loto'Aniu et al, ) and local loss to the atmosphere (Thorne & Kennel, ; Horne & Thorne, ; Summers et al, ). For the former, the primary observational evidence is the radially peaked PSD profile of relativistic electrons (Turner et al, ; Mann et al, ); for the latter, the observational evidences frequently mentioned in previous works are the wave‐related electron precipitation at low altitudes (Lorentzen et al, ; Millan et al, ; Miyoshi et al, ; Tsurutani et al, ; Breneman et al, ) and the flat‐top PAD characteristic (Usanova et al, ; Engebretson et al, ; Su et al, ; Shprits et al, ). Here on the basis of the analysis of an extreme radiation belt electron loss event observed by RBSP and POES on 27 February 2014, we present new evidence for the EMIC wave‐driven local precipitation loss of relativistic electrons in the heart of the outer radiation belt: The RBSP‐observed radial profile of the relativistic electron PSD appeared to be quasi‐monotonic, in contrast to the peaked type of previously reported events (e.g., Turner et al, ; Mann et al, ).…”

“…The whistler mode plasmaspheric hiss (Horne & Thorne, ; Summers et al, ; Breneman et al, ) and magnetosonic waves (Roberts & Schulz , Shprits; ) may also contribute to the local precipitation loss of relativistic electrons. As shown in the previous simulations (e.g., Li et al, ; Su et al, ), the typical loss time scale of the off‐equatorially mirroring relativistic electrons driven by plasmaspheric hiss waves (a few days to hundreds of days) is much larger than that associated with EMIC waves (hours) (e.g., Summers et al, , ).…”

“…Wave‐driven pitch angle scattering can reduce the altitudes of electron mirror points, and collisions with atmospheric particles yield the precipitation loss of electrons. The primary characteristic of radial loss is a radially peaked PSD profile (Turner et al, ; Mann et al, ), while the main evidences for local loss are the flat‐top PAD characteristic (Usanova et al, ; Engebretson et al, ; Su et al, ; Shprits et al, ) and the wave‐related electron precipitation observed at low altitudes (Lorentzen et al, ; Millan et al, ; Miyoshi et al, ; Tsurutani et al, ; Breneman et al, ; Zhang, Halford, et al, ).…”

Recent advances in radiation belt dynamics and wave-particle interactions in the Earth’s inner magnetosphere

“…Combining plasmaspheric hiss observations from the Van Allen Probes and precipitation electron observations from the BARREL balloons data that measures bremsstrahlung X-rays generated by electrons colliding with the Earth's atmosphere, Breneman et al (2015) have shown that the electron loss and hiss magnitude are highly coherent, and both are modulated by fluctuations of density and magnetic field in ULF range (maybe related to the ULF wave). The timescales could be as short as one to twenty minutes, while the space scale was comparable to the size of the plasmasphere.…”