Study of Pc1 pearl structures observed at multi-point ground stations in Russia, Japan, and Canada

Abstract

We investigate possible generation mechanisms of Pc1 pearl structures using multi-point induction magnetometers in Athabasca in Canada, Magadan in Russia, and Moshiri in Japan. We selected two Pc1 pulsations that were simultaneously observed at the three stations and applied a polarization analysis. In case 1, on 8 April 2010, Pc1 pearl structures were slightly different in some time intervals at different stations, and their polarization angles varied depending on the frequencies at the three stations. Case 2, on 11 April 2010, showed Pc1 pearl structures that were similar at different stations, and their polarization angle was independent of frequency at all three stations. In order to understand these differences, we performed two simple model calculations of Pc1 pearl structures under different conditions. The first model assumes that Pc1 waves propagated from a latitudinally extended source with different frequencies at different latitudes to the observation points, representing beating of these waves in the ionosphere. The second model considers Pc1 waves for which different frequencies are mixed at a point source to cause the beating at the source point, indicating that the Pc1 pearl structures are generated in the magnetosphere. The first model shows slightly different waveforms at different stations. In contrast, the second model shows identical waveforms at different stations. From these results, we conclude that, in case 1, Pc1 pearl structures were caused by beating in the ionosphere. On the other hand, in case 2, they were the result of magnetospheric effects. We suggest that beating processes in the ionosphere could be one of the generation mechanisms of Pc1 pearl structures.

A Statistical Study of EMIC Waves Associated With and Without Energetic Particle Injection From the Magnetotail

“…The AE index was less than 25 nT during this 2-hr interval (Figure 3a), and there were no significant variations of the proton and electron fluxes at GOES 15 (Figures 3f-3h), indicating extremely quiet geomagnetic conditions. In These structured EMIC waves are called "pearl structures" (e.g., Jun et al, 2014Jun et al, , 2016Paulson et al, 2014) that have often been observed during quiet geomagnetic conditions in the morning sector within the inner magnetosphere (Paulson et al, 2016). During this EMIC event, we can see a clear H + flux enhancement at 0.1-1 keV (Figure 3e).…”

“…Figures c and d present structured H + band EMIC waves from 1118 to 1210 UT, representing a long duration event. These structured EMIC waves are called “pearl structures” (e.g., Jun et al, , ; Paulson et al, ) that have often been observed during quiet geomagnetic conditions in the morning sector within the inner magnetosphere (Paulson et al, ). During this EMIC event, we can see a clear H + flux enhancement at 0.1–1 keV (Figure e).…”

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

“…In previous studies, the amplitude modulation mechanisms for Pc1 pulsations were classified into two types, the beating effect in the ionosphere [Pope, 1964;Nomura et al, 2011;Jun et al, 2014] and the propagating effect in the magnetosphere along the magnetic field line [Obayashi, 1965;Guglielmi et al, 1996;Mursula et al, 1999]. However, the observed high correlation between the Pc1 and BG3 (aurora) intensities suggests that rather than these mechanisms, the quasiperiodic Pc1 amplitude modulations are generated at the waveparticle interaction region in the magnetosphere.…”

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

“…The Pc1 waves propagate horizontally through the ionospheric duct over a few thousand kilometers (e.g., Fraser 1975;Kawamura et al 1981). 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).…”