[P-EM15] Dynamics of Magnetosphere and Ionosphere

[PEM15-07] Spatio-temporal variation of the mean energy of precipitating electron flux in poleward-propagating pulsating auroras

*Mizuki Fukizawa¹, Yoshimasa Tanaka¹, Yasunobu Ogawa¹, Keisuke Hosokawa², Yoshizumi Miyoshi³, Yoshiya Kasahara⁴, Shoya Matsuda⁴, Ayako Matsuoka⁵, Mariko Teramoto⁶ (1.National Institute of Polar Research, 2.University of Electro-Communications, 3.Nagoya University, 4.Kanazawa University, 5.Kyoto University, 6.Kyushu Institute of Technology)

Keywords:Pulsating aurora, Chorus wave, Computed tomography

Pulsating auroras are quasi-periodic blinking auroras, with intervals ranging from a few seconds to tens of seconds. They occur over a wide area, from just after auroral breakup to the day side. Recently, they have attracted attention due to the suggestion that relativistic electrons precipitating within pulsating auroras contribute to the destruction of mesospheric ozone. The electrons that drive pulsating auroras are scattered in pitch angle through wave-particle interactions near the magnetic equator, as revealed by magnetospheric satellites. However, satellite observations cannot distinguish between spatio-temporal variations and the distinction between pulsating auroras that blink in situ and auroras that repeat propagation remains unresolved. Therefore, the present study aims to reveal the spatio-temporal variability of the poleward propagating pulsating aurora within the torch observed during magnetic storms by computer tomography using auroral images acquired by several all-sky cameras. Additionally, the study discusses the relationship between poleward-propagating pulsating auroras and chorus waves based on simultaneous observations by the Arase satellite and ground-based optical measurements.
A magnetic storm caused by a coronal mass ejection occurred on 23–24 March 2023. During the recovery phase from 01:03–01:10 UT on March 26, 2023, poleward-propagating pulsating auroras were observed within the common field of view of all-sky cameras at Tromsø (69.58°N, 19.22°E), Skibotn (69.35°N, 20.36°E), and Kilpisjärvi (69.05°N, 20.78°E). The poleward-propagating pulsating auroras observed in this event repeatedly propagated with a period of about 10 seconds from the non-propagating patch auroras at the torch's centre towards the torch's high-latitude boundary. Using the aurora images at wavelengths of 427.8 nm and 557.7 nm observed at these three locations, we conducted Generalized-Aurora Computer Tomography (G-ACT) and reconstructed the 2D distribution of the average energy of the precipitating electron flux in poleward-propagating and non-propagating patch auroras. As a result, the reconstructed average energy of the precipitating electron flux for the poleward-propagating pulsating auroras was found to be 17–28 keV, while for the non-propagating patch auroras, it was 31–37 keV, indicating that the poleward-propagating pulsating auroras had lower average electron energy by a few keV to tens of keV.
Although the Arase satellite's footprint was not within the field of view of the all-sky cameras in the aforementioned event, on 29 March 2017, from 00:28–00:30 UT, simultaneous observations of poleward-propagating pulsating auroras were conducted by the Arase satellite and the all-sky cameras at Sodankylä (67.42°N, 26.39°E). When the satellite's footprint passed through pulsating auroras propagating in the east-west direction or expanding arc-like pulsating auroras, a one-to-one correspondence was confirmed between the time variation of the lower-band chorus (LBC) waves observed at a magnetic latitude of about -15 degrees and the aurora emission intensity observed at the satellite's footprint. Conversely, the amplitude of the LBC wave was small (about 10 pT) during the poleward-propagating pulsating aurora, and no one-to-one correspondence with the temporal variation of the auroral emission intensity was confirmed. It can be inferred from this that the LBC waves that generate poleward propagating pulsating auroras cannot propagate to high latitudes in the magnetosphere. This finding is consistent with the results of G-ACT, which showed lower average electron energy for poleward-propagating pulsating auroras.