[P-EM09] Dynamics of Magnetosphere and Ionosphere

[PEM09-24] New results of auroral hiss observations on the ground at L=5.5 in Northern Europe

★Invited Papers

*Jyrki Manninen¹, Natalia G. Kleimenova^2,3, Yury Fedorenko⁴, Olga Lebed⁴, Alexander Kozlovsky¹, Alexander Nikitenko⁴, Liudmila Gromova⁵ (1.Sodankyla Geophysical Observatory, University of Oulu, Sodankylä, Finland, 2.Schmidt Institute of Physics of the Earth RAN, Moscow, Russia, 3.Space Research Institute RAN, Moscow, Russia, 4.Polar Geophysical Institute, Apatity, Russia, 5.Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation RAN, Moscow, Russia)

Keywords:Auroral hiss, substorm, growth phase

Auroral hiss is a well-known type of nighttime natural VLF emission with a noise-like structure generated by the Cherenkov instability of precipitating soft electrons above the ionosphere. Auroral hiss occurrence up to 39 kHz was studied in the equatorward region of the auroral oval at the Finnish station Kannuslehto (KAN, MLAT = 64.2°N) during 11 winter months in 2015-2018. During this time interval, 98 isolated and rather powerful magnetic substorms were recorded over Scandinavia. In 93% of the substorms studied, an auroral VLF hiss was recorded at the same time as enhancement of field-aligned currents (FACs). FACs are caused by soft electron precipitation which could be a plausible source of the auroral VLF hiss generation. For the first time, it was found that auroral VLF hiss occurrence in the equatorward region of the auroral oval is a typical signature of the substorm growth phase.

Also a few examples of simultaneous auroral hiss observations at Lovozero, Russia (LOZ, MLAT = 64.2°N) will be shown. LOZ is located at the same magnetic latitude as KAN, but 400 km to east from KAN. Simultaneous observations can be used for direction finding of auroral hiss events.

Figure presents a survey of the auroral hiss event on 23 December 2016 at 17-19 UT. From top to bottom: a) the auroral hiss spectrogram; b) the auroral keogram from Abisko; c) the auroral keogram from Sodankyla; d) the IL indicator of magnetic activity; and e) the south-west quarters of the global map (in geomagbnetic coordinate´s) of the field-aligned currents (FACs) according to the AMPERE data. Blue arrows point the time of these map of auroral hiss at KAN was accompanied by the upward FAC increasing in the premidnight sector constructions. The upward FACs are marked by red and the downward FACs, by blue. The small circles indicate the location of KAN.