JpGU-AGU Joint Meeting 2020

Presentation information

[E] Oral

P (Space and Planetary Sciences ) » P-EM Solar-Terrestrial Sciences, Space Electromagnetism & Space Environment

[P-EM13] Dynamics of Magnetosphere and Ionosphere

convener:Aoi Nakamizo(Applied Electromagnetic Research Institute, National Institute of Information and Communications Technology), Mitsunori Ozaki(Faculty of Electrical and Computer Engineering, Institute of Science and Engineering, Kanazawa University), Akiko Fujimoto(Kyushu Institute of Technology), Yuka Sato(Nippon Institute of Technology)

[PEM13-14] 3D current system of auroral vortices in the discrete arc estimated by auroral tomography and local KRM methods

*Yoshimasa Tanaka1,2,3, Yasunobu Ogawa1,3, Akira Kadokura1,2,3, Takanori Nishiyama1,3, Akimasa Yoshikawa4, Bjorn Gustavsson5, Kirsti Kauristie6, Carl-fredrik Enell7, Urban Brandstrom8, Tima Sergienko8, Alexander Kozlovsky9, Tero Raita9, Heikki Vanhamaki10 (1.National Institute of Polar Research, 2.Polar Environment Data Science Center, 3.The Graduate University for Advanced Studies, 4.Department of Earth and Planetary Sciences, Kyushu University, 5.The Arctic University of Norway, 6.Finnish Meteorological Institute, 7.EISCAT Scientific Association, 8.Swedish Institute of Space Physics, 9.Sodankyla Geophysical Observatory, 10.University of Oulu)

Keywords:aurora tomography, 3D structure of aurora, 3D current system, magnetosphere ionosphere coupling, auroral vortex structure

In the magnetosphere-ionosphere coupling, three-dimensional (3D) current system on the ionosphere is essential to understand how electromagnetic energy and momentum are transported between the magnetosphere and ionosphere. However, it is generally difficult to derive the 3D current system of the auroral phenomena from the observation. One of the methods to obtain the 3D current system on the ionosphere is so-called Kamide-Richmond-Matsushita (KRM) method. This method calculates the 3D current system from the ionospheric equivalent current and the ionospheric conductivity; the former is derived from the ground-based magnetometer network data and the latter is often given by the empirical model.
In this study, we estimate the 3D current system of auroral vortices in the discrete arc, which were observed with the multiple imagers with a wavelength of 427.8 nm in Northern Europe at 22:15-22:20 UT on March 14, 2015, by using the local KRM method (Vanhamaki et al., 2006). The advantage of this study is to obtain the ionospheric conductivity from the imager network observation. We applied the auroral computed tomography method to the multiple monochromatic images and obtained 3D distribution of the volume emission rate of 427.8 nm every 10 second during 22:15-22:20 UT. By using the theoretical model and the empirical atmosphere model, we converted the volume emission rate to the electron density in the ionosphere. As a result, we obtained the height-integrated conductivity in the horizontal area of 150 km x 300 km. The ionospheric equivalent current was derived every 10 second from the IMAGE chain magnetometer data. Finally, we estimated 3D current system around the discrete arcs by using the local KRM method. The results showed that pairs of upward and downward field-aligned current (FAC) drifted eastward along the arc together with the auroral vortices. It was found that the distribution of the upward and downward FACs was distorted, which was caused by the divergent ionospheric Hall current due to the non-uniform ionospheric conductivity.