[P-EM12] Dynamics of the Inner Magnetospheric System

[PEM12-14] A case study to estimate energy spectra of pulsating auroral electrons from cosmic noise absorption and auroral brightness

*Shin-ichiro Oyama^1,2, Miyamoto Taishiro^1,6, Tero Raita³, Keisuke Hosokawa⁴, Yoshizumi Miyoshi¹, Yasunobu Ogawa², Satoshi Kurita⁵ (1.Institute for Space-Earth Environmental Research, Nagoya University, 2.National Institute of Polar Research, 3.Sodankyla Geophysical Observatory, University of Oulu, 4.University of Electro-Communications, 5.Research Institute for Sustainable Humanosphere, Kyoto University, 6.Nippon Steel Corporation Nagoya Works)

Keywords:pulsating aurora, ionosphere, riometer

This study focused on a pulsating aurora event associated with aurora morphological changes in Fennoscandia at early morning time on 7 March 2017. A high-speed sampling all-sky camera captured equatorward development of the pulsating auroral patch in association with a substorm centered at Greenland/North America region. Of particular interest of this event is interconnection between the auroral intensity and the cosmic noise absorption (CNA) derived from three riometers aligned meridionally in Finland (from north to south: Ivalo, Sodankylä and Rovaniemi). The analysis was made by dividing optical measurements into two oscillation components; longer and shorter than 40 s, that is, non-pulsating and pulsating auroral modulations. The interrelation showed linear correlation and change of the inclination would be interpreted as hardening or softening of the precipitating electron spectrum. In terms of the low-pass component, the inclination of the CNA-vs-intensity interrelation increased at the three riometer latitudes at the substorm recovery phase. On the other hand, in terms of the high-pass component, the inclination decreased at Rovaniemi (lower latitude) but stayed uniform at Sodankylä (higher latitude). These features suggest that the precipitating electron spectrum has softened in the low-pass or non-pulsating auroral component but the spectrum has hardened in the high-pass or pulsating auroral component at the lower side in latitudes of the auroral patch region. This study proposes a new application of the riometer-camera measurement to examination of the auroral particle precipitation.