The Detached Auroras Induced by the Solar Wind Pressure Enhancement in Both Hemispheres From Imaging and In Situ Particle Observations

Abstract

This paper presents simultaneous detached proton auroras that appeared in both hemispheres at 11:06 UT, 08 March 2012, just 2 min after a sudden solar wind pressure enhancement (~11:04 UT) hit the Earth. They were observed under northward interplanetary magnetic field Bz condition and during the recovery phase of a moderate geomagnetic storm. In the Northern Hemisphere, Defense Meteorological Satellite Program/Special Sensor Ultraviolet Spectrographic Imager observed that the detached arc occurred within 60°–65° magnetic latitude and covered a few magnetic local time (MLT) hours ranging from 0530 to 0830 MLT with a possible extension toward noon. At the same time (11:06 UT), Polar Orbiting Environment Satellites 19 detected a detached proton aurora around 1300 MLT in the Southern Hemisphere, centering ~62° magnetic latitude, which was at the same latitudes as the northern detached arc. This southern aurora was most probably a part of a dayside detached arc that was conjugate to the northern one. In situ particle observations indicated that the detached auroras were dominated by protons/ions with energies ranging from around 20 keV to several hundreds of keV, without obvious electron precipitations. These detached arcs persisted for less than 6 min, consistent with the impact from pressure enhancement and the observed electromagnetic ion cyclotron (EMIC) waves. It is suggested that the increasing solar wind pressure pushed the hot ions in the ring current closer to Earth where the steep gradient of cold plasma favored EMIC wave growth. By losing energy to EMIC waves the energetic protons (>20 keV) were scattered into the loss cone and produced the observed detached proton auroras.

Isolated Auroral Spots Observed by DMSP/SSUSI

“…The proton aurora spots can be also well outside the plasmapause (Yahnin et al, ). Previous works also indicated that the wave‐particle interactions between EMIC waves and energetic ions were account for subauroral proton spots (Yahnin et al, ), isolated proton arcs (Sakaguchi et al, ), isolated proton auroras (Miyoshi et al, ; Ozaki et al, ), and dayside detached auroras (Zhou et al, ). Therefore, the results of the present work further support the association between the isolated auroral spots, particle precipitations, plasmapause location, and Pc1 pulsations as reported by previous investigations (Sakaguchi et al, ; Yahnin et al, ; Miyoshi et al, ; Ozaki et al, ).…”

“…Previous works have suggested that the energetic protons/ions related to isolated spots, isolated arc, and dayside detached auroras can be scattered by EMIC waves through a mechanism named cyclotron resonance (Yahnin et al, 2007;Sakaguchi et al, 2007;Ozaki et al, 2018;Zhou et al, 2018). The ion cyclotron instability is expected to produce both the growth of the EMIC waves and the scattering of energetic ions into the loss cone (Yahnin et al, 2007).…”

A Possible Mechanism on the Detachment Between a Subauroral Proton Arc and the Auroral Oval

“…The cyclotron resonance between EMIC waves and ring current ions has been suggested to be a dominant mechanism that causes the ions to precipitate into the ionosphere, producing auroral phenomena at subauroral latitudes (Sakaguchi et al., 2008; Yahnin & Yahnina, 2007; Yahnin et al., 2007; Yahnina et al., 2008; Yuan et al., 2010; Zhou et al., 2018). These subauroral phenomena are classified into several types for their different morphologies, which are likely related to different physical processes in the solar wind‐magnetosphere‐ionosphere system (Frey, 2007).…”

Direct Observation of Low‐Energy Electron Precipitation in the Subauroral Region

“…It is proposed that dayside detached auroras are produced by energetic protons, with energies above approximately 10 keV, originating from the ring current (Zhang et al., 2002; S. Zhou et al., 2018). The sudden increase of solar wind dynamic pressure was suggested to cause ion temperature anisotropy, and the resulting EMIC waves then scatter ring current ions producing these auroras (Hubert et al., 2003; Zhang et al., 2002, 2008; S. Zhou et al., 2018). Previous studies indicate that the precipitations of energetic protons at the subauroral region are the main causes of afternoon detached auroral arcs, also known as subauroral proton arcs (Yuan et al., 2010).…”

“…It has been suggested that interaction with electromagnetic ion cyclotron (EMIC) waves plays a crucial role in scattering and precipitating energetic ring current ions at subauroral latitudes (Nakamura et al., 2021; Sakaguchi et al., 2008; Yahnina et al., 2008; Yuan et al., 2010; S. Zhou et al., 2021). It is proposed that dayside detached auroras are produced by energetic protons, with energies above approximately 10 keV, originating from the ring current (Zhang et al., 2002; S. Zhou et al., 2018). The sudden increase of solar wind dynamic pressure was suggested to cause ion temperature anisotropy, and the resulting EMIC waves then scatter ring current ions producing these auroras (Hubert et al., 2003; Zhang et al., 2002, 2008; S. Zhou et al., 2018).…”