[P-EM13] Dynamics of the Inner Magnetospheric System

[PEM13-P03] Experimental evidence of aurora brightness dependence on chorus intensity and energetic electron flux

*Rui Chen^1,2, Yoshizumi Miyoshi², Xinliang Gao¹, Quanming Lu¹, Keisuke Hosokawa³, Yasunobu Ogawa⁴, Shin-ichiro Oyama^2,4, Yoshiya Kasahara⁵, Shoya Matsuda⁵, Satoko Nakamura², Ayako Matsuoka⁶, Iku Shinohara⁷, Satoshi Kasahara⁸, Shoichiro Yokota⁹, Tomo Hori², Kuni Keika⁸ (1.University of Science and Technology of China, 2.Nagoya University, 3.The University of Electro-Communications, 4.National Institute of Polar Research, 5.Kanazawa University, 6.Kyoto University, 7.Japan Aerospace Exploration Agency, 8.University of Tokyo, 9.Osaka University)

Keywords:Aurora brightness, Chorus intensity, Energetic electron flux, Arase observation, Ground-based observation

The joint observations with ground-based all-sky cameras and magnetospheric satellites reveal that diffuse aurora is caused by precipitating electrons which can be scattered by chorus waves. Chorus waves with quasi-periodic intensity modulations, called chorus bursts, lead to modulations in aurora brightness, exhibiting a series of on-off transitions (named pulsating aurora). Hosokawa et al. (2020) reported a joint observation (on March 30, 2017) with ground-based EMCCD cameras (aurora) and the Arase satellite (chorus waves), and they found a clear one-to-one correspondence between each pulsating aurora pulse and chorus burst. However, there has been no direct analysis investigating the parameters that control aurora brightness.

By reanalyzing the joint observation reported by Hosokawa et al. (2020), we reveal that chorus wave intensity and energetic electron flux control the aurora brightness. In this event (from 13:00 UT to 13:30 UT on March 30, 2017), the observed chorus bursts always had a large intensity (> ~1 mV/m), but the brightness of the aurora pulse was relatively weak (< ~2700 counts) before ~13:07 UT, and the brightness became > ~2800 counts (even up to ~3300 counts) after ~13:07 UT. Firstly, we compared the relation between the aurora brightness and the intensity of chorus waves, and found a positive correlation between them if removing the data before 13:07 UT. Then, we estimated the cyclotron resonant energies of chorus waves based on the cold plasma dispersion relation and further analyzed the corresponding energetic electron fluxes. Before ~13:07 UT, the energetic electron fluxes were much smaller, well explaining the weakening of the aurora brightness. In summary, the aurora brightness depends on the values of chorus intensity and energetic electron flux, and energetic electron flux reaching a threshold appears to be a prerequisite for the formation of auroras.