Observations of precipitation energies during different types of pulsating aurora

Abstract

Abstract. Pulsating aurora (PsA) is a diffuse type of aurora with different structures switching on and off with a period of a few seconds. It is often associated with energetic electron precipitation (>10 keV) resulting in the interaction between magnetospheric electrons and electromagnetic waves in the magnetosphere. Recent studies categorize pulsating aurora into three different types – amorphous pulsating aurora (APA), patchy pulsating aurora (PPA), and patchy aurora (PA) – based on the spatial extent of pulsations and structural stability. Differences in precipitation energies of electrons associated with these types of pulsating aurora have been suggested. In this study, we further examine these three types of pulsating aurora using electron density measurements from the European Incoherent Scatter (EISCAT) VHF/UHF radar experiments and Kilpisjärvi Atmospheric Imaging Receiver Array (KAIRA) cosmic noise absorption (CNA) measurements. Based on ground-based all-sky camera images over the Fennoscandian region, we identified a total of 92 PsA events in the years between 2010 and 2020 with simultaneous EISCAT experiments. Among these events, 39, 35, and 18 were APA, PPA, and PA types with a collective duration of 58, 43, and 21 h, respectively. We found that, below 100 km, electron density enhancements during PPAs and PAs are significantly higher than during APA. However, there are no appreciable electron density differences between PPA and APA above 100 km, while PA showed weaker ionization. The altitude of the maximum electron density also showed considerable differences among the three types, centered around 110, 105, and 105 km for APA, PPA, and PA, respectively. The KAIRA CNA values also showed higher values on average during PPA (0.33 dB) compared to PA (0.23 dB) and especially APA (0.17 dB). In general, this suggests that the precipitating electrons responsible for APA have a lower energy range compared to PPA and PA types. Among the three categories, the magnitude of the maximum electron density shows higher values at lower altitudes and in the late magnetic local time (MLT) sector (after 5 MLT) during PPA than during PA or APA. We also found significant ionization down to 70 km during PPA and PA, which corresponds to ∼200 keV of precipitating electrons.

D-region impact area of energetic electron precipitation during pulsating aurora

“…They are commonly observed in the recovery phase of substorms, with the greatest occurrence rates in the early morning sector (Jones et al, 2011;Bland et al, 2019;Grono and Donovan, 2020). The energetic electron precipitation (EEP) that produces PsA is thought to arise from chorus wave activity, whereby electrons from the radiation belts are scattered into the atmospheric loss cone (Thorne et al, 2010;Kasahara et al, 2018). The precipitating electrons typically have energies up to the order of 10-100 keV, depositing their energy into the upper mesosphere/lower thermosphere region at approximately 70-120 km altitude (Fang et al, 2008;Turunen et al, 2009;Miyoshi et al, 2010;Tesema et al, 2020b).…”

Simultaneous Pulsating Aurora and Microburst Observations With Ground‐Based Fast Auroral Imagers and CubeSat FIREBIRD‐II

“…On the other hand, the upper-band chorus waves cause background stable precipitations (Evans et al, 1987). Recent studies (e.g., Grono & Donovan, 2020;Tesema et al, 2020;Yang et al, 2019) indicated the relationship between the precipitating energy and the shape of the pulsating aurora. The recent reviews about the pulsating aurora and diffuse aurora are found in Nishimura et al (2020).…”

Types of pulsating aurora: Comparison of model and EISCAT electron density observations

“…This is clearly seen in the EISCAT electron density measurements as a significant ionization below 80 km. Similar local time evolution of hardening precipitation was recently investigated by Tesema et al (2020b) in a more statistical approach including EISCAT and optical data from the same geographical area. However, the cut-off altitude of the model is 80 km, which causes a large discrepancy between the model and the EISCAT electron density below 80 km.…”

“…In addition, the third category, patchy aurora (PA), consists of very persistent structure with limited pulsation at the patch edges. The energy of electrons associated with the pulsating aurora types are different (Yang et al, 2019;Tesema et al, 2020b). From a total of 92 PsA events Tesema et al (2020b) compared the D region ionization level obtained by EISCAT radars for different types of PsA and suggested that PPA is the dominant type of aurora affecting the D region atmosphere.…”