On the Factors Controlling the Relationship Between Type of Pulsating Aurora and Energy of Pulsating Auroral Electrons: Simultaneous Observations by Arase Satellite, Ground-Based All-Sky Imagers and EISCAT Radar

Abstract

Pulsating Aurora (PsA) is one of the major classes of diffuse aurora associated with precipitation of a few to a few tens of keV electrons from the magnetosphere. Recent studies suggested that, during PsA, more energetic (i.e., sub-relativistic/relativistic) electrons precipitate into the ionosphere at the same time. Those electrons are considered to be scattered at the higher latitude part of the magnetosphere by whistler-mode chorus waves propagating away from the magnetic equator. However, there have been no actual cases of simultaneous observations of precipitating electrons causing PsA (PsA electrons) and chorus waves propagating toward higher latitudes; thus, we still do not quite well understand under what conditions PsA electrons become harder and precipitate to lower altitudes. To address this question, we have investigated an extended interval of PsA on 12 January 2021, during which simultaneous observations with the Arase satellite, ground-based all-sky imagers and the European Incoherent SCATter (EISCAT) radar were conducted. We found that, when the PsA shape became patchy, the PsA electron energy increased and Arase detected intense chorus waves at magnetic latitudes above 20°, indicating the propagation of chorus waves up to higher latitudes along the field line. A direct comparison between the irregularities of the magnetospheric electron density and the emission intensity of PsA patches at the footprint of the satellite suggests that the PsA morphology and the energy of PsA electrons are determined by the presence of “magnetospheric density ducts,” which allow chorus waves to travel to higher latitudes and thereby precipitate more energetic electrons.