5:15 PM - 6:45 PM
[PEM17-P10] The Role of IAR and Alfven Waves in Auroral Acceleration Region Formation: Elucidating the Initial Formation Process through 3-Dimensional Collisional Hall MHD Simulation.
Keywords:Auroral Acceleration Region, MHD simulation
The auroral acceleration region, located within the upward current region, is where the quasi-static parallel electric field generates precipitating electrons with energies in the several keV range. This region is crucial for the formation of discrete auroras. The characteristics of quasi-static electric fields have been revealed by artificial satellite observations. It is well known that these fields are established in the M-I(magnetosphere-ionosphere) coupling system at altitudes from 3,000 km to 10,000 km. This is where magnetospheric hot and tenuous plasma, ionospheric cold and dense plasma, and auroral cavity plasma, composed of ionospheric ion beams and magnetospheric electrons, are mixed [Ergun et al., 2004, Marklund et al., 2021]. Theoretical and numerical simulation approaches, which solve the Vlasov-Poisson equation system under appropriate assumptions, have been conducted. These simulations have confirmed results consistent with observations. [Ergun et al., 2000, Main et al., 2006]. Despite numerous previous research efforts aimed at elucidating the acceleration region, the development and distribution of potential distribution, the transportation process of plasma originating from different regions, and the formation and development processes of the acceleration region remain unclear. It is necessary to understand the time and spatial development, from before the establishment of acceleration region, of physical quantities along the magnetic field line. Especially the Alfvén waves, which carry information in the MHD description, and the density distribution, which is important from the viewpoint of current continuity, are important quantities.
At the point of before the establishment of acceleration region, the Ionospheric Alfven resonator (IAR), which is caused by the Alfven wave phase velocity gradient above the ionosphere, play crucial role. In the IAR, Alfven waves are trapped by their own phase velocity gradient and form a standing wave structure. Moreover, the ponderomotive force, a time-averaged nonlinear force, accelerates the plasma along the field line within that structure, changes the plasma distribution, and produces the cavity regions [Sydorenko et al., 2008]. In our research, we consider that this IAR cavity region is significant not only from the viewpoint of Alfven acceleration [Lysak 1993], but also for ionospheric plasma transportation in the acceleration formation process.
In addition, previous research on IAR [Sydorenko et al., 2008, 2013, 2018] utilized a two-dimensional model to describe the magnetosphere-ionosphere (M-I) coupling system, focusing solely on the Pedersen current as the ionospheric response. However, the Hall current also influences the ionospheric response and provides feedback to the magnetosphere [Yoshikawa et al., 2013a, b; Nakamizo and Yoshikawa, 2018]. Therefore, the Hall current effect should be incorporated into the simulation model to accurately reproduce the Alfven wave structure.
Hence, in our research, we are developing a 3-dimensional dipole coordinate collisional Hall MHD simulation that reproduces the Alfven wave structure under the IAR in the M-I coupling system, including the Hall current, as well as the accompanying development of plasma distribution. In the presentation, we explain the role of the IAR and Alfven waves in the auroral acceleration formation process and report on the developing simulation results.
At the point of before the establishment of acceleration region, the Ionospheric Alfven resonator (IAR), which is caused by the Alfven wave phase velocity gradient above the ionosphere, play crucial role. In the IAR, Alfven waves are trapped by their own phase velocity gradient and form a standing wave structure. Moreover, the ponderomotive force, a time-averaged nonlinear force, accelerates the plasma along the field line within that structure, changes the plasma distribution, and produces the cavity regions [Sydorenko et al., 2008]. In our research, we consider that this IAR cavity region is significant not only from the viewpoint of Alfven acceleration [Lysak 1993], but also for ionospheric plasma transportation in the acceleration formation process.
In addition, previous research on IAR [Sydorenko et al., 2008, 2013, 2018] utilized a two-dimensional model to describe the magnetosphere-ionosphere (M-I) coupling system, focusing solely on the Pedersen current as the ionospheric response. However, the Hall current also influences the ionospheric response and provides feedback to the magnetosphere [Yoshikawa et al., 2013a, b; Nakamizo and Yoshikawa, 2018]. Therefore, the Hall current effect should be incorporated into the simulation model to accurately reproduce the Alfven wave structure.
Hence, in our research, we are developing a 3-dimensional dipole coordinate collisional Hall MHD simulation that reproduces the Alfven wave structure under the IAR in the M-I coupling system, including the Hall current, as well as the accompanying development of plasma distribution. In the presentation, we explain the role of the IAR and Alfven waves in the auroral acceleration formation process and report on the developing simulation results.