Explaining occurrences of auroral kilometric radiation in Van Allen radiation belts

Abstract

Auroral kilometric radiation (AKR) is a strong terrestrial radio emission and dominates at higher latitudes because of reflection in vicinities of the source cavity and plasmapause. Recently, Van Allen Probes have observed occurrences of AKR emission in the equatorial region of Earth's radiation belts but its origin still remains an open question. Equatorial AKR can produce efficient acceleration of radiation belt electrons and is a risk to space weather. Here we report high‐resolution observations during two small storm periods 4–6 April and 18–20 May 2013 and show, using a 3‐D ray tracing simulation, that AKR can propagate downward all the way into the equatorial plane in the radiation belts under appropriate conditions. The simulated results can successfully explain the observed AKR's spatial distribution and frequency range, and the current results have a wide application to all other magnetized astrophysical objects in the universe.

Global Occurrences of Auroral Kilometric Radiation Related to Suprathermal Electrons in Radiation Belts

“…This is because enhanced magnetospheric convection can maintain strong injections of plasmasheet suprathermal electrons in the presence of strong storms, consequently providing more free energy for AKR generation when those suprathermal electrons move along the geomagnetic field into the polar cavity region. Then under suitable circumstances, AKR emissions propagate downward into the radiation belts and are observed by Van Allen Probes (Xiao et al, ).…”

“…The recent high‐precision observation from Van Allen Probes (Kurth et al, ) has reported the presence of AKR in radiation belts. Xiao et al () have demonstrated that AKR can propagate into the equatorial plane in the radiation belts under appropriate conditions by three‐dimensional ray‐tracing modeling.…”

A Concise Empirical Formula for the Field‐Aligned Distribution of Auroral Kilometeric Radiation Based on Arase Satellite and Van Allen Probes

“…The major reason is probably as follows: when AKR emissions propagate downward to the equatorial plane, they should encounter magnetospheric reflections because the cutoff frequency f cut increases due to the increasing background density. Previous three‐dimensional ray tracing study (Xiao et al., 2016) has demonstrated that AKR emissions with higher (lower) wave frequency tend to stay in lower (higher) L‐shells of the equatorial plane. We check all AKR samples and find that about 80 % of total AKR samples exhibit higher peak wave frequency (≥200 kHz) on the nightside and about 40 % of total AKR samples have lower peak wave frequency (<200 kHz) on the dayside.…”

“…Those studies which used the data from high latitudes, focus on the generation in the source region and/or propagation characteristics in the magnetosphere. Kurth et al (2015) have reported the presence of AKR in the equatorial region of radiation belts via observations from Van Allen Probes, and Xiao et al (2016) have proposed that AKR can propagate down to the equatorial plane from source regions by the three-dimensional ray-tracing method. Zhao et al (2019) have presented the global occurrence of AKR emissions in the radiation belts and confirmed that they are strongly associated with suprathermal electron injections from the plasma sheet.…”

Dominant Roles of High Harmonics on Interactions Between AKR and Radiation Belt Relativistic Electrons

“…This study is important for better modeling of AKR-induced radiation belt electron dynamics.Recently, AKR has been observed in the radiation belt by Van Allen Probes (Kurth et al, 2015). Xiao et al (2016) have proposed that AKR can propagate down to extremely low-latitude regions even through the equatorial plane from source cavities by the three-dimensional ray tracing method. The statistical results of the AKR occurrences have shown that AKR exists on a broad region of L = 3-6.5 and the whole magnetic local time (Zhao et al, 2019).…”