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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/angeo-2019-40
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/angeo-2019-40
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: regular paper 26 Mar 2019

Submitted as: regular paper | 26 Mar 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Annales Geophysicae (ANGEO).

Swarm field-aligned currents during a severe magnetic storm of September 2017

Renata Lukianova1,2 Renata Lukianova
  • 1Space Research Institute, 117997 Moscow, Russia
  • 2Institute of Earth Science, Saint Petersburg State University, 199034 Saint Petersburg, Russia

Abstract. Swarm satellites observations are used to characterize the extreme behavior of large- and small-scale field-aligned currents (FACs) during the severe magnetic storm of September 2017. Evolution of the current intensities and the equatorward displacement of FACs are analyzed while the satellites cross the pre-midnight, pre-noon, dusk and dawn sectors in both hemispheres. The equatorward boundaries of FACs mainly follow the dynamics of ring current (as monitored in terms of the SYM-H index). The minimum latitude of the FAC boundaries is limited to 50° MLat, below which saturation occurs. The FAC densities are very variable and may increase dramatically, especially in the nightside ionosphere during the storm-time substorms. At the peak of substorm, the average FAC densities reach 3 μA/m2, while the quite level is below 0.1 μA/m2. The dawn–dusk asymmetry is manifested in the enhanced dusk-side R2 FACs in both hemispheres. Filamentary high-density structures are always observed confirming that a substantial fraction of R1/R2 FACs is composed of many small-scale currents. In the pre-noon sector, the bipolar structures (7.5 km width FACs of opposite polarities adjacent to each other) dominate, while in the post-midnight sector the upward and downward FACs tend to form more latitudinally extended structures of a certain polarity. The most intense small-scale FACs (up to ~80 μA/m2) is observed just in the post-midnight sector. Simultaneous magnetic and plasma perturbations indicate that this structure is likely a current system of a mesoscale auroral arc.

Renata Lukianova
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Renata Lukianova
Renata Lukianova
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Latest update: 19 Sep 2019
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Short summary
During the most intense storm of the solar cycle 24, the magnetosphere-ionosphere interaction, which is primarily associated with field-aligned currents (FAC) and particle precipitation, was much stronger than usual. Measurements onboard the polar-orbiting satellite show that the equatorial boundaries of FAC are shifted equatorward as low as 50° MLat. The intensities of FAC increase dramatically the peaks of the storm-time substorm. The extreme instantaneous FACs is up to ~80 μA/m2.
During the most intense storm of the solar cycle 24, the magnetosphere-ionosphere interaction,...
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