A Multi‐Instrument Approach to Determining the Source‐Region Extent of EEP‐Driving EMIC Waves

Abstract

Recent years have seen debate regarding the ability of electromagnetic ion cyclotron (EMIC) waves to drive EEP (energetic electron precipitation) into the Earth's atmosphere. Questions still remain regarding the energies and rates at which these waves are able to interact with electrons. Many studies have attempted to characterize these interactions using simulations; however, these are limited by a lack of precise information regarding the spatial scale size of EMIC activity regions. In this study we examine a fortuitous simultaneous observation of EMIC wave activity by the RBSP-B and Arase satellites in conjunction with ground-based observations of EEP by a subionospheric VLF network. We describe a simple method for determining the longitudinal extent of the EMIC source region based on these observations, calculating a width of 0.75 hr MLT and a drift rate of 0.67 MLT/hr. We describe how this may be applied to other similar EMIC wave events. Plain Language SummaryThe Earth is surrounded by the Van Allen radiation belts, rings of high-energy charged particles trapped by the Earth's magnetic field. These particle populations are constantly changing, driven by forces from the Sun, Earth, and from the belts themselves. One of the most important drivers of this dynamism is the interaction between particles and electromagnetic waves. One such wave species, known as Electromagnetic Ion Cyclotron (EMIC) waves, has come under scrutiny recently due to experimental results calling into question the theoretical energy limits of their interactions with radiation belt electrons. Studying these waves and their interactions is hampered by our inability to accurately determine the size of the source region of these waves. In this study, we investigate a single EMIC wave event observed simultaneously by two separate satellites and use a network of ground-based radio wave receivers to estimate the size of the EMIC region. We also explain how the method used in this study may be generalized to other EMIC wave events. This method will allow us to carry out statistical analysis of the size of EMIC wave regions in general, aiding future research into the impacts of these waves on the radiation belts.

Modulation of Pc1 Wave Ducting by Equatorial Plasma Bubble

“…Second, Kim et al (2018) did not thoroughly discuss possible intersatellite differences of the wave intensity and electron density observed by the Swarm-A and Swarm-C, which fly in a tight formation. The separation of the two satellites (~1.5°in longitude or 0.1 hr in local time) is smaller than reported scale sizes of EMIC wave source regions: for example, up to 0.7 hr in local time in Blum et al (2016, Table 1), >0.3 hr in local time in Blum et al (2017, Summary), and 0.75 hr in local time in Hendry et al (2020). Hence, differences in Pc1 amplitudes observed by the two Swarm satellites, if any, are largely attributable to wave propagation effects through two different ionospheric paths.…”

Evening Side EMIC Waves and Related Proton Precipitation Induced by a Substorm

“…Due to the multipoint EMIC wave observations in space, we can estimate the minimum extent of the region occupied by the waves, which is significant for estimates of their roles in both ring current ion dynamics and relativistic electron precipitation (see also Hendry et al., 2020). In our case, VAP‐A and VAP‐B observe the EMIC waves simultaneously from 16:15 to 16:30 UT when the distance between them was 1.5 h in MLT.…”

On the Impacts of Ions of Ionospheric Origin and Their Composition on Magnetospheric EMIC Waves

“…At the same time, sub-MeV electron precipitation associated with EMIC waves has been reported with statistical lower cut off energy down to 300 keV (e.g. Hendry et al, 2020;Capannolo et al, 2019). Many of the low Earth orbit (LEO) satellite observations used to infer the electron precipitation caused by EMIC waves have not been energy-resolved and future direct measurements will continue to help characterize the spectrum of energetic electrons impacted by EMIC waves (cf.…”