Modeling the electromagnetic ion cyclotron wave‐induced formation of detached subauroral proton arcs

Abstract

[1] Detached dayside proton arcs have been recently observed at Earth with the IMAGE FUV instrument as subauroral arcs separated from the main oval and extending over several hours of local time in the afternoon sector. We investigate the mechanisms causing the proton precipitation during two subauroral arc events that occurred on 23 January 2001 and 18 June 2001. We employ our kinetic physics-based model coupled with a dynamic plasmasphere model and calculate the growth rate of electromagnetic ion cyclotron (EMIC) waves self-consistently with the evolving ring current H + , O + , and He + ion distributions. Modeled plasmaspheric densities agree well with in situ observations from geosynchronous LANL satellites and duskside plasmapause observations from IMAGE EUV but overestimate the drainage plume extent toward noon on 18 June. Global images of precipitating H + ions are obtained and compared with IMAGE observations of proton arcs. We find that EMIC waves are preferentially excited, and proton precipitation maximizes, within regions of spatial overlap of energetic ring current protons and dayside plasmaspheric plumes and along steep density gradients at the plasmapause. The model matches very well the temporal and spatial evolution of FUV observations on 23 January. The predicted location of the proton precipitation on 18 June extends a few hours westward of the observations, and an offset of 2 hours in the convection electric field is needed to reproduce well the evolution of the proton arc. This study indicates that cyclotron resonant wave-particle interactions are a viable mechanism for the generation of subauroral proton arcs.Citation: Jordanova, V. K., M. Spasojevic, and M. F. Thomsen (2007), Modeling the electromagnetic ion cyclotron wave-induced formation of detached subauroral proton arcs,

Limitation of energetic ring current ion spectra

“…In fact, there is still much current interest in ion pitch angle scattering by EMIC waves in the context of ring current dynamics. This is evidenced by the substantial literature that relates EMIC waves to ion precipitation resulting in ring current decay [e.g., Cornwall et al, 1970;Erlandson and Ukhorskiy, 2001;Summers, 2005;Fraser et al, 2006;Jordanova et al, 2007;Yahnin and Yahnina, 2007;Engebretson et al, 2008;Sakaguchi et al, 2008;Spasojevic et al, 2011;Xiao et al, 2012;Yuan et al, 2014]. In the present work, we treat EMIC wave-ion interactions as linear or quasi-linear, in common with most previous studies.…”

Energetic ions scattered into the loss cone with observations of the Cluster satellite

“…In the isotropic zones, the curved field line geometry in the magnetotail has been considered as a key mechanism causing the protons in the central plasma sheet (CPS) to be pitch angle scattered into the loss cone and subsequently precipitate in the ionosphere (e.g., Sergeev et al, 1983;Buchner and Zelenyi, 1986;Ashour-Abdalla et al, 1990;Liang et al, 2013). In the anisotropic zones, the NOAA spacecraft can observe enhancement of the precipitating ion flux at subauroral latitudes, which is a result of precipitating RC ions scattered into the loss cone by EMIC waves (Yahnin et al, 2002(Yahnin et al, , 2006Jordanova, et al, 2007;Yuan et al, 2012b). To better reveal the key mechanisms scattering protons into the loss cone, in situ satellite observations of simultaneous loss of energetic protons and EMIC waves are very necessary.…”

“…In addition, with the substorminduced electric field some plasma sheet protons can further be injected into the current ring region. The interaction between ring current (RC) ions and EMIC waves in the plasmapause or plasmaspheric plumes can lead to the scattering of RC ions into the loss cone and precipitating into the atmosphere at subauroral latitudes (Jordanova et al, 2007;Yahnin et al, 2009;Spasojević and Fuselier, 2009;Yuan et al, 2010). As a result, the low-altitude NOAA spacecraft crossing the auroral zone from high to low latitudes firstly detects an isotropic proton flux distribution and subsequently detects a drop of the proton flux within the loss cone and still a strong flux of trapped particles at lower latitudes (the anisotropic zones) (Yahnin et al, 2006;Yuan et al, 2011Yuan et al, , 2012bYuan et al, , 2013.…”

“…In the dayside outer magnetosphere, EMIC waves in Pc2 band can also be generated high off the equator and in the regions of the minimum of magnetic field within Shabansky orbits (Liu et al, 2012). Through the wave-particle interactions, EMIC waves can scatter ring current (RC) ions and radiation belt relativistic electrons into the loss cone, leading to loss into the atmosphere (Yahnin et al, 2006;Jordanova, et al, 2007;Sakaguchi et al, 2008;Morley et al, 2009;Yuan et al, 2010Yuan et al, , 2012aYuan et al, , b, 2013Carson et al, 2013;Li et al, 2014;Usanova et al, 2010Usanova et al, , 2014. Therefore, EMIC waves may play an important role in the dynamics of the ring current and radiation belt through wave-particle interaction.…”

Characteristic dimension of electromagnetic ion cyclotron wave activity in the magnetosphere

“…EMIC waves play an important role in extracting energy from the hot, anisotropic ions and causing pitch angle scattering of energetic ions and relativistic electrons into the loss cone [Cornwall et al, 1970;Jordanova et al, 2007]. In order to better understand the role of EMIC waves in the dynamics of the magnetosphere, spatial dimensions of the EMIC wave activity need to be known.…”