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.
Highlights
The interaction between solar wind and the magnetosphere results in particle precipitation into the Earth’s atmosphere through many different processes
By inspecting 11 years of allsky cameras (ASCs) images from the Finnish Meteorological Institute (FMI)-Magnetometers–Ionospheric Radars–Allsky Cameras Large Experiment (MIRACLE) network in combination with European Incoherent Scatter (EISCAT) electron density measurements, we identified Pulsating aurora (PsA) events based on classification implemented in Grono and Donovan (2018) and Yang et al (2019)
The PsA type between 02:00 and 03:10 UT is labeled as patchy aurora (PA), because the EISCAT radar beam lies within this type of PsA as indicated by dashed red lines
Summary
The interaction between solar wind and the magnetosphere results in particle precipitation into the Earth’s atmosphere through many different processes. Particles from the plasma sheet and radiation belts are accelerated and scattered into a loss cone to eventually collide with the species in the Earth’s polar atmosphere. These collisions cause the atmospheric gas to glow in different shimmering bands of color in the sky, called aurora. An auroral spectrum ranges from ultraviolet to infrared wavelengths depending on the type of atmospheric gas that undergoes emission. The electrons generating aurora have energies ranging from 100 eV to 100 keV, which affects the atmosphere by ionizing and changing the chemistry (Rees, 1969). The auroras are varied in appearance due to different magnetospheric pro-
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