11:00 AM - 1:00 PM
[PEM10-P08] A Numerical Simulation of the Formation of Poleward Boundary Intensifications of Auroral Emission due to Ionospheric Polarization
Keywords:PBI, M-I coupling, induction effect, conductivity gradient, numerical simulation
We performed a numerical analysis of the generation mechanism of Poleward Boundary Intensifications (PBIs) of auroral emission due to ionospheric polarization. PBIs have been considered as an ionospheric manifestation of the distant reconnection in the magnetotail [e.g., Lyons et al., 2011]. However, this theory contradicts the recently reported PBI characteristics [e.g., Zou et al., 2014] as pointed out by Ohtani and Yoshikawa (2016). They also proposed a new idea of the PBI formation based on the ionospheric polarization, and tested the idea by conducting a numerical analysis confirming that the ionospheric polarization causes radiated FAC larger than the incident FAC.
However, their study did not consider the time evolution of the electric conductance, therefore only the initial process of PBIs was investigated. In the present study, we take this into account and investigate the evolution process of PBIs. Moreover, we also consider the advection of ionospheric conductance in the direction perpendicular to the magnetic field in addition to the conventional description of the time evolution of ionospheric conductance, which considers only the effect of precipitating electrons associated with the FAC [e.g., Sato, 1978]. Furthermore, in previous studies, the analysis was done with the electrostatic process, but in our model, the assumption was eliminated by introducing the induction effect in the rotational-current system.
As a result, the electrical conductance and the induced FAC significantly changed. It was found that the precipitating electrons were more important for the time variation of the conductance than the advection. This caused the changes in the spatial structure of the induced upward FAC and successfully reproduces the northward expanding structure of PBIs. In addition, although the contribution of the Hall polarization to the induced upward FAC is small at the initial process, it induces an upward FAC comparable to the Pedersen polarization in the evolution process, suggesting the importance of the Hall polarization.
In this presentation, we will discuss these results as well as outstanding issues to be addressed in the future. At present, there are some problems in the numerical system, and we will try to resolve them and eventually construct a model that can be applied to the magnetosphere-ionosphere coupling system in general by considering the spatial structure of the conductivity and the induction effect.
However, their study did not consider the time evolution of the electric conductance, therefore only the initial process of PBIs was investigated. In the present study, we take this into account and investigate the evolution process of PBIs. Moreover, we also consider the advection of ionospheric conductance in the direction perpendicular to the magnetic field in addition to the conventional description of the time evolution of ionospheric conductance, which considers only the effect of precipitating electrons associated with the FAC [e.g., Sato, 1978]. Furthermore, in previous studies, the analysis was done with the electrostatic process, but in our model, the assumption was eliminated by introducing the induction effect in the rotational-current system.
As a result, the electrical conductance and the induced FAC significantly changed. It was found that the precipitating electrons were more important for the time variation of the conductance than the advection. This caused the changes in the spatial structure of the induced upward FAC and successfully reproduces the northward expanding structure of PBIs. In addition, although the contribution of the Hall polarization to the induced upward FAC is small at the initial process, it induces an upward FAC comparable to the Pedersen polarization in the evolution process, suggesting the importance of the Hall polarization.
In this presentation, we will discuss these results as well as outstanding issues to be addressed in the future. At present, there are some problems in the numerical system, and we will try to resolve them and eventually construct a model that can be applied to the magnetosphere-ionosphere coupling system in general by considering the spatial structure of the conductivity and the induction effect.