[P-EM09] Dynamics of Magnetosphere and Ionosphere

[PEM09-14] Current and future perspectives on 3D analysis of aurora

★Invited Papers

*Yoshimasa Tanaka^1,2,3, Yasunobu Ogawa^1,2,3, Akira Kadokura^1,2,3, Bjorn Gustavsson⁴, Kirsti Kauristie⁵, Enell Carl-fredrik⁶, Urban Brandstrom⁷, Tima Sergienko⁷, Alexander Kozlovsky⁸, Tero Raita⁸, Mizuki Fukizawa⁹, Takeshi Sakanoi⁹, Keisuke Hosokawa¹⁰ (1.National Institute of Polar Research, 2.Polar Environment Data Science Center, Joint Support-Center for Data Science Research, Research Organization of Information and Systems, 3.The Graduate University for Advanced Studies, SOKENDAI, 4.The Arctic University of Norway, 5.Finnish Meteorological Institute, 6.EISCAT Scientific Association, 7.Swedish Institute of Space Physics, 8.Sodankyla Geophysical Observatory, 9.Planetary Plasma and Atmospheric Research Center, Graduate School of Science, Tohoku University, 10.Department of Communication Engineering and Informatics, University of Electro-Communications)

Keywords:aurora, tomography analysis, discrete aurora, pulsating aurora, energy distribution of precipitating electrons, EISCAT_3D

Aurora Computed Tomography (ACT) is an analysis method to reconstruct three-dimensional (3D) structure of auroral luminosity from monochromatic auroral images simultaneously taken by multi-point imager network on the ground. The ACT method enables us to derive the altitude profile of the auroral luminosity, corresponding to the energy distribution of precipitating electrons from the magnetosphere. Another advantage of the ACT is the capability to derive the 3D distribution of the electron density, resulting in the electrical conductivity, in the ionospheric E and F regions at high-time resolution. The auroras are the electromagnetic phenomena generated by the magnetosphere-ionosphere (M-I) coupling process, so it is essential to understand the 3D current system in the M-I system. The 3D current system can be estimated by using the ionospheric conductivity obtained from the ACT analysis, with the ionospheric electric field from the radars or the ionospheric equivalent current from the magnetometers.
So far, we have applied the ACT analysis to several discrete aurora events to reconstruct the 3D distribution of the optical emission and the energy distribution of the precipitating electrons. It was demonstated that the altitude profile of the optical emission at the wavelength of 427.8 nm obtained by the ACT method is similar to the ionospheric density profile simultaneously observed with the EISCAT radar. Recently, we also succeeded in the 3D reconstruction of the pulsating auroral patches. In these case studies, the ionospheric electron density converted from the optical emission using the theoretical and empirical models was underestimated compared with that observed by the EISCAT radar. The radars and optical imagers are complementary to each other, because the radars have a high range resolution, while the imagers have a high angular resolution. In order to combine these different kinds of data effectively, we have developed the Generalized - Aurora Computed Tomography (G-ACT) method, which is capable of retrieving the differential number flux of precipitating electrons from multi-instrument data, such as the monochromatic images from the multiple imagers, the ionospheric electron density from the radars, and cosmic noise absorption from the imaging riometers. This method enables more accurate reconstruction of 3D aurora, even in case it is difficult to reconstruct by the optical data only. In particular, it is expected that the G-ACT method will be useful for the research on the auroral 3D structure by the EISCAT_3D, which is a multiple-site phased-array incoherent scatter radar system that is planned to be operated in 2022. We are planning to apply the G-ACT technique to data obtained from both the EISCAT_3D radar and the imager networks, which are being constructed by the international collaboration, to extract the 3D current system accompanied by various auroral phenomena.