A direct link between chorus emissions and pulsating aurora on timescales from milliseconds to minutes: A case study at subauroral latitudes

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  • Mitsunori Ozaki
    Graduate School of Natural Science and Technology Kanazawa University Kanazawa Japan
  • Satoshi Yagitani
    Graduate School of Natural Science and Technology Kanazawa University Kanazawa Japan
  • Kaoru Sawai
    Graduate School of Natural Science and Technology Kanazawa University Kanazawa Japan
  • Kazuo Shiokawa
    Institute for Space-Earth Environmental Research Nagoya University Nagoya Japan
  • Yoshizumi Miyoshi
    Institute for Space-Earth Environmental Research Nagoya University Nagoya Japan
  • Ryuho Kataoka
    National Institute of Polar Research Tachikawa Japan
  • Akimasa Ieda
    Institute for Space-Earth Environmental Research Nagoya University Nagoya Japan
  • Yusuke Ebihara
    Research Institute for Sustainable Humanosphere Kyoto University Uji Japan
  • Martin Connors
    Center for Science Athabasca University Athabasca Canada
  • Ian Schofield
    Center for Science Athabasca University Athabasca Canada
  • Yuto Katoh
    Graduate School of Science Tohoku University Sendai Japan
  • Yuichi Otsuka
    Institute for Space-Earth Environmental Research Nagoya University Nagoya Japan
  • Naoki Sunagawa
    Institute for Space-Earth Environmental Research Nagoya University Nagoya Japan
  • Vania K. Jordanova
    Los Alamos National Laboratory Los Alamos New Mexico USA

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<jats:title>Abstract</jats:title><jats:p>A correlation was observed between chorus emissions and pulsating aurora (PA) from observations at Athabasca (<jats:italic>L</jats:italic>≈4.3) in Canada at 9:00–9:20 UT on 7 February 2013, using an electron multiplying charge‐coupled device camera and a VLF loop antenna with sampling rates of 110 Hz and 100 kHz, respectively. Pulsating aurora having a quasiperiodic variation in luminosity and a few hertz modulation was observed together with chorus emissions consisting of a group of successive rising‐tone elements. The repetition period and modulation frequency of the PA are in good agreement with those of the modulated chorus. After 9:11 UT, the temporal features of the aurora became aperiodic PA of indistinct modulation. Simultaneously, the rising‐tone chorus turned into chorus emissions consisting of numerous rising‐tone elements. The equatorial geomagnetic field inhomogeneity calculated using the Tsyganenko 2002 model shows a decreasing trend during the period. This result is consistent with nonlinear wave growth theory having a small geomagnetic field inhomogeneity, which contributes to a decrease in the threshold amplitude to trigger discrete chorus elements. These observations show a close connection between chorus emissions and PA on timescales from milliseconds for generation of discrete chorus elements on the microphysics of wave‐particle interaction to minutes for the variations of the geomagnetic field inhomogeneity related with the substorm activity.</jats:p>

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