Fast modulations of pulsating proton aurora related to subpacket structures of Pc1 geomagnetic pulsations at subauroral latitudes

Abstract

To understand the role of electromagnetic ion cyclotron (EMIC) waves in determining the temporal features of pulsating proton aurora (PPA) via wave‐particle interactions at subauroral latitudes, high‐time‐resolution (1/8 s) images of proton‐induced N2+ emissions were recorded using a new electron multiplying charge‐coupled device camera, along with related Pc1 pulsations on the ground. The observed Pc1 pulsations consisted of successive rising‐tone elements with a spacing for each element of 100 s and subpacket structures, which manifest as amplitude modulations with a period of a few tens of seconds. In accordance with the temporal features of the Pc1 pulsations, the auroral intensity showed a similar repetition period of 100 s and an unpredicted fast modulation of a few tens of seconds. These results indicate that PPA is generated by pitch angle scattering, nonlinearly interacting with Pc1/EMIC waves at the magnetic equator.

Microscopic Observations of Pulsating Aurora Associated With Chorus Element Structures: Coordinated Arase Satellite‐PWING Observations

“…Next, the ratio of the auroral intensity related to discrete elements to that for subpacket structures is almost the same as for the case of a pulsating proton aurora and Pc1 waves at subauroral latitudes (Ozaki et al, 2016). The association between pulsating proton aurora and Pc1 waves is close to that between pulsating electron aurora and chorus waves; thus, the observed intensity modulations of tens of milliseconds can be possibly related to the chorus subpacket structures.…”

Discovery of 1 Hz Range Modulation of Isolated Proton Aurora at Subauroral Latitudes

“…The BG3 images are wideband but are colocated with Hbeta (Hydrogen Balmer ®, wavelength of 486.1 nm) emissions, which are a signature of energetic (several tens of keV) proton precipitation. The other IPA event on 12 November 2015 is the same as that presented in Ozaki et al (2016). Both pulsating IPA events are highly correlated with the Pc1 intensity variations, which are calculated as the integration from 0.35 to 0.90 Hz in Figure 1d.…”

“…Isolated proton aurora (IPA) allows the diagnosis of localized wave-particle interaction in the inner magnetosphere. Recently, pulsating IPA was discovered at subauroral latitudes (Nomura et al, 2016;Ozaki et al, 2016). The likely IPA generation mechanism is pitch angle scattering of protons by electromagnetic ion cyclotron (EMIC) waves undergoing wave-particle interactions at the magnetic equator (e.g., Albert, 2003;Jordanova et al, 2001;Kennel & Petschek, 1966;Shoji & Omura, 2014), which leads to proton precipitation in the energy range from 30 to 800 keV (Hyun et al, 2014;Yahnin et al, 2007).…”

Ground-based instruments of the PWING project to investigate dynamics of the inner magnetosphere at subauroral latitudes as a part of the ERG-ground coordinated observation network

“…Thus comparison of these EMCCD data with data from the loop antenna will be very interesting to investigate such a wave-particle interactions, though usually the magnetospheric ELF/VLF emissions are masked by the highly conductive ionosphere during pulsating aurora. Comparison of the EMCCD camera images of isolated proton aurora with EMIC waves observed by induction magnetometer will be more promising to study the interaction of highenergy ions and EMIC waves (e.g., Ozaki et al 2016). Comparison with the Arase and Van Allen Probes satellites will be essential to study these wave-particle interaction processes by monitoring their spatial and temporal motion by using this ground EMCCD camera.…”

“…As shown by Jun et al (2014Jun et al ( , 2016, comparison of Pc1 pearl structures (amplitude modulation) at different stations may help understanding the generation mechanisms of the pearl structure through beating of different waves during duct propagation. Comparison with all-sky airglow/aurora imager data gives us an interesting opportunity to monitor interaction between EMIC waves and ring-current protons/relativistic electrons (e.g., Sakaguchi et al 2007Sakaguchi et al , 2008Sakaguchi et al , 2012Miyoshi et al 2008;Nomura et al 2011Nomura et al , 2012Nomura et al , 2016Ozaki et al 2016). …”