Polarization of Pc1/EMIC waves and related proton auroras observed at subauroral latitudes

Abstract

[1] We have investigated the polarization of Pc1 geomagnetic pulsations and related proton auroras at subauroral latitudes, using an induction magnetometer and an all-sky camera at Athabasca, Canada (54.7°N, 246.7°E, magnetic latitude (mlat) 61.7°N). Isolated proton auroras often appear in association with Pc1 pulsations, because of proton scattering by electromagnetic ion cyclotron (EMIC) waves in the magnetosphere. We used the proton aurora as a proxy for the location and size of the Pc1 ionospheric source. For 27 Pc1 events with simultaneously observed proton auroras over 4 years from September 7, 2005 to September 6, 2009, we calculated the distances between the Pc1 ionospheric source and the observation site, normalized by the scale size of the source. We tried three different definitions of the scale size of Pc1 ionospheric source to calculate the normalized distances. We found that the rotation angle q between the Pc1 polarization ellipse and the direction to the proton aurora changes from 90°to 0°as the normalized distance increases. For the definition of the scale sizes that gives most clear q-transition from 90°to 0°, the transition occurs at the normalized distance $2.0-4.0, while it was $1.0-2.0 by the model calculation of Fujita and Tamao (1988). The averaged major axes tend to point toward the proton aurora at larger distances. The difference of the transition location may imply that the Pc1 ionospheric sources are larger than the isolated proton auroras, or that the inhomogenuity of the ionospheric conductivity by the proton precipitation affects the transition distances.

Global characteristics of Pc1 magnetic pulsations during solar cycle 23 deduced from CHAMP data

“…They frequently occur in the subauroral region (e.g. Fraser et al, 1996;Nomura et al, 2012) and in the auroral region (e.g. Roldugin et al, 2013).…”

“…At mid-latitudes the polarization obviously depends on frequency (Nomura et al, 2011), and the major axis of the polarization ellipse points to the source location when the observation point is far from the source (Nomura et al, 2012).…”

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

“…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). …”

Pc1–2 auroral pulsations

“…A relationship between the appearance of geomagnetic Pc1 pulsations on the ground and the occurrence of patchy proton auroras over an observatory by IMAGE satellite observations was reported by Yahnin et al [2007] and Yahnina et al [2008], but there is no data about the intensity of the aurora. A simultaneous occurrence of proton auroras and Pc1 pulsations at subauroral latitudes has been also reported by Sakaguchi et al [2007Sakaguchi et al [ , 2008 and Nomura et al [2012].…”

“…This camera uses the FE-0.8-MAO (4.2) "fish-eye" lenses with no filters. Its maximum sensitivity is in the range 500-600 nm; that is, the intensity of 557.7 nm emission makes a major contribution to the images, as it was in the proton aurora investigation by Nomura et al [2012]. The frame rate is one per second, and the resolution is 360 Â 360 pixels with 2 bytes per pixel.…”