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- Title
Characteristics of Auroral Electron Precipitation at Geomagnetic Latitude 67° Over Tromsø.
- Authors
Tesfaw, Habtamu W.; Virtanen, Ilkka I.; Aikio, Anita T.
- Abstract
We use the EISCAT incoherent scatter radar data measured in years 2001–2021 to study statistical characteristics of 1–100 keV electron precipitation at 66.7° MLAT over Tromsø. Peak energies, auroral powers and number fluxes of precipitating electrons are derived from electron density altitude profiles measured along the geomagnetic field line during periods of no photoionization. The method allows us to include energetic 30–100 keV electrons, which are poorly covered in earlier satellite‐based studies. Locations of the radar within the auroral oval are determined using a model with the 1‐hr Hpo geomagnetic index as input. The average peak energy of precipitating electrons increases almost monotonically from evening (18 MLT) to morning hours (09 MLT). The 30–50 keV electrons dominate the energetic electron precipitation before 06 MLT, after which the 50–100 keV precipitation becomes dominant. Large auroral powers (>60 mWm−2) are observed in the 18–02 MLT sector in the main auroral oval. We obtain occurrence rate of electron precipitation in Tromsø by calculating the fraction of data points with auroral power larger than 2 mWm−2. The occurrence rate peaks during the declining phases of solar cycles (sc), in 2002–2004 for sc23 and in 2015–2017 for sc24, caused by variations in geomagnetic activity. In addition, the occurrence rate has maxima during March and September, minimum in December to January, and it increases monotonically from evening to morning hours, reaching maximum at 05–06 MLT. Plain Language Summary: The Earth's magnetic field is almost vertical at high latitudes, and it connects the upper part of the Earth's atmosphere to the surrounding magnetosphere. This connection allows electrons to precipitate from the magnetosphere down to the upper atmosphere, and causes the visual auroral displays, geomagnetic disturbances, and ionization of the neutral atmospheric particles through collisions. We use 21 years of radar data measured by the EISCAT incoherent scatter radar in Tromsø, northern Norway, to study statistical characteristics of auroral electron precipitation. The radar data allows us to include not only 1–30 keV but also 30–100 keV energies, which have been poorly covered in previous satellite‐based studies. We find that the radar observes auroral electron precipitation most frequently during morning hours (5–6 magnetic local time), and during September and March equinox months. In addition, electron precipitation occurs most frequently during years immediately after the sunspot maximum years. Electrons that have higher energies precipitate more commonly during morning hours than evening hours, and large energy and number fluxes occur more frequently in the evening and pre‐midnight hours than in post‐midnight and morning hours. Key Points: We use EISCAT UHF incoherent scatter radar data to study the 1–100 keV electron precipitation at 66.7° MLAT observed during 21 yearsThe auroral electron precipitation occurrence rate as observed by the radar reaches 70% in the 05–06 MLT sector of the main auroral ovalElectron precipitation with 50–100 keV peak energies is more common than with 30–50 keV peak energies after 06 MLT
- Subjects
AURORAS; ELECTRON distribution; SOLAR cycle; PHOTOIONIZATION; ELECTRONS; ATMOSPHERIC ionization; ATMOSPHERE; GEOMAGNETISM
- Publication
Journal of Geophysical Research. Space Physics, 2023, Vol 128, Issue 7, p1
- ISSN
2169-9380
- Publication type
Article
- DOI
10.1029/2023JA031382