[P-EM11] Dynamics of the Inner Magnetospheric System

[PEM11-13] Pulsating aurora immediately after the onset of a substorm observed by the Arase satellite, all-sky imager, and digital camera

*Sota Nanjo¹, Olivier Staiger², Akira Kadokura³, Yoshimasa Tanaka³, Ryuho Kataoka³, Yoshizumi Miyoshi⁴, Satoko Nakamura⁴, Yasunobu Ogawa³, Yoshiya Kasahara⁵, Shoya Matsuda⁵, Satoshi Kasahara⁶, Yoichi Kazama⁷, Shoichiro Yokota⁸, Tomoaki Hori⁴, Ayako Matsuoka⁹, Kunihiro Keika⁶, Chae-Woo Jun⁴, Iku Shinohara¹⁰, Keisuke Hosokawa¹ (1.The University of Electro-Communications, 2.Auroral Guide, 3.National Institute of Polar Research, 4.ISEE, Nagoya University, 5.Kanazawa Uniersity, 6.The University of Tokyo, 7.Institute of Astronomy and Astrophysics, Academia Sinica, 8.Osaka University, 9.Kyoto University, 10.Institute of Space and Astronautical Science)

Keywords:Pulsating Aurora, Arase satellite, Digital camera observation

We report an auroral substorm event observed by the Arase satellite and ground-based cameras that occurred at 23:30 UT on 7 October 2018. The relationship between substorms and the pulsating aurora (PsA) has been investigated since the late 1960s (Akasofu, 1968). PsAs are often observed during the post-onset, which primarily correspond to the recovery phase (Partamies et al., 2017). In addition, since they appear most frequently on the morning side (Jones et al., 2011), many previous studies focused on PsAs on the morning side and during late recovery phases. As a result, few studies have focused on PsAs that appear at an early stage of the expansion phase, i.e., soon after the expansion phase onset. Consequently, the condition and process triggering the PsA are not yet well understood. In order to examine PsA right after substorm onset, this study analyzes simultaneous observations of PsAs over Iceland during a substorm using the Arase satellite, an all-sky imager (ASI), and a digital mirror-less camera. We attempted to infer the parameters that contribute to the triggering of the PsA. In this event, the ASI data demonstrated that PsAs appeared 10 minutes after the onset, spread over the entire sky in 5 minutes, and lasted for more than an hour. During this period, the Arase satellite, whose footprint was located inside the FOV of the ASI in Húsafell, detected a rapid increase in the electron flux (injection) at the onset. However, it was still 40 minutes later when the satellite started to see chorus waves. In addition, the panchromatic ASI at Húsafell is not capable of detecting a few Hz internal modulations because it has only one channel sensitive to emissions over a wide wavelength range, including 557.7 nm. Fortunately, an auroral guide, who stayed near the observatory by chance, captured PsAs using a digital mirror-less camera with three wavelength bands of RGB. His video showed temporal fluctuations of several Hz only in the red and blue channels, indicating the existence of internal modulations. Such modulation was less frequent immediately after onset, albeit the result from limited FOVs and periods observation. Based on these observations, we discuss the trigger parameter of the PsA and the cause of the delay of chorus waves relative to the optical emission.