University of Oulu

Thor, S., Kullen, A., Cai, L., Katrougkalou, M. C., & Zhang, Y. (2023). Interhemispheric conjugacy of multiple transpolar arcs. Geophysical Research Letters, 50, e2023GL103816.

Interhemispheric conjugacy of multiple transpolar arcs

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Author: Thor, S.1; Kullen, A.1; Cai, L.2;
Organizations: 1Division of Space and Plasma Physics, School of Electrical Engineering and Computer Science, KTH Royal Institute of Technology, Stockholm, Sweden
2Space Physics and Astronomy, University of Oulu, Oulu, Finland
3The Johns Hopkins University Applied Physics Laboratory, Baltimore, MD, USA
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 3 MB)
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Language: English
Published: American Geophysical Union, 2023
Publish Date: 2023-08-25


Multiple transpolar arcs appearing simultaneously in the polar cap have gained much interest in recent years. By analyzing Defense Meteorological Satellite Program Special Sensor Ultraviolet Spectrographic Imagers data, we report for the first time, that less than half of the multiple arc events occur simultaneously in both hemispheres. In 60% of the cases, multiple arcs appear in only one hemisphere. There is a clear difference in interplanetary magnetic field (IMF) conditions for those two groups. Conjugate multiple arcs appear on average during stronger northward IMF and smaller IMF clock angles than non-conjugate multiple arcs. Only non-conjugate multiple arcs show a dependence on IMF BX. They form in the northern (southern) hemisphere during negative (positive) BX. An IMF BX induced interhemispheric asymmetry in the magnetospheric field line topology might explain why multiple arcs appear sometimes in only one hemisphere.

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Series: Geophysical research letters
ISSN: 0094-8276
ISSN-E: 1944-8007
ISSN-L: 0094-8276
Volume: 50
Issue: 10
Article number: e2023GL103816
DOI: 10.1029/2023GL103816
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Funding: This work is supported by the Swedish National Space Agency DNR-155A/17 and DNR 2021-00134.
Dataset Reference: The multiple arc events examined in this study are a subset of the DMSP SSUSI TPA data set in Kullen et al. (2023), and have been processed with GeospaceLAB (, a python package for managing and visualizing data in space physics (Cai et al., 2022). All TPA events in Kullen et al. (2023) have been selected by visual inspection of DMSP SSUSI images in the LBH short wavelength range from F16, F17, F18 and F19 according to the selection criteria described above. The original DMSP SSUSI gif-images in LBH short can be downloaded from One can select the year, day of year (doy), and wavelength as input on the webpage. For the analysis of the solar wind conditions during multiple arcs, 1-min resolution OMNI solar wind velocity and interplanetary magnetic field (IMF) data are obtained from the CDAWeb ( The Earth dipole tilt angle was computed using the Geopack Python package (
Copyright information: © 2023 The Authors. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.