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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Preprints
https://doi.org/10.5194/angeo-2020-43
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/angeo-2020-43
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  07 Jul 2020

07 Jul 2020

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A revised version of this preprint was accepted for the journal ANGEO and is expected to appear here in due course.

Observations of precipitation energies during different types of pulsating aurora

Fasil Tesema1,2, Noora Partamies1,2, Hilde Nesse Tyssøy2, and Derek McKay3 Fasil Tesema et al.
  • 1The University Centre in Svalbard (UNIS), Norway
  • 2Birkeland Centre for Space Science, University of Bergen, Norway
  • 3NORCE Norwegian Research Centre AS, Tromsø, Norway

Abstract. Pulsating aurora (PsA) is a diffuse type of aurora with different structures switching on and off with a period of few seconds. It is often associated with energetic electron precipitation (10 keV) resulted 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 hrs, 43 hrs, and 21 hrs, 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 km, 105 km, 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 during PPA at lower altitudes and in the late MLT sector (after 5 MLT). We also found significant ionization down to 70 km during PPA and PA, which corresponds to ~ 200 keV energies of precipitating pulsating aurora electrons.

Fasil Tesema et al.

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Fasil Tesema et al.

Fasil Tesema et al.

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Latest update: 24 Oct 2020
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Short summary
In this study, we present the ionization level from EISCAT radars experiments and cosmic noise absorption level from KAIRA riometer observations during pulsating auroras. We found thick layers of ionization that reach down to 70 km (harder precipitation) and higher cosmic noise absorption during patchy pulsating aurora compared to amorphous pulsating and patchy auroras.
In this study, we present the ionization level from EISCAT radars experiments and cosmic noise...
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