University of Oulu

Kullen, A., Thor, S., & Cai, L. (2023). The question of transpolar arc conjugacy: New results from comparing solar wind data and dipole tilt distribution of five different datasets. Journal of Geophysical Research: Space Physics, 128, e2022JA030987.

The question of transpolar arc conjugacy : new results from comparing solar wind data and dipole tilt distribution of five different datasets

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Author: Kullen, Anita1; Thor, S.1; Cai, L.2
Organizations: 1Space and Plasma Physics, KTH Royal Institute of Technology, Stockholm, Sweden
2Space Physics and Astronomy, University of Oulu, Oulu, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 2 MB)
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Language: English
Published: American Geophysical Union, 2022
Publish Date: 2023-01-04


In this work, we investigate the interhemispheric transpolar arc (TPA) conjugacy using four previously published datasets based on Polar UV images, DMSP particle data, and IMAGE images, and a new TPA list based on DMSP SSUSI images during 1 Sep to 15 Oct 2015. IMF Bₓ and the Earth’s dipole tilt have often been suggested to influence the TPA conjugacy, as both induce a north-south asymmetry on the magnetosphere. However, by comparing these parameters at TPA formation with the background distribution for each dataset, we find that neither the dipole tilt nor Bₓ plays a major role for the TPA conjugacy in four of the five datasets. The well-known correlation between initial TPA location and IMF By appears in all datasets with information about the TPA formation. In addition, we find that a minority of dawnside TPAs form during the “wrong” By sign. In the northern (southern) hemisphere, dawn TPAs appear also during weakly duskward (dawnward) IMF. Due to the polar orbit of DMSP satellites, TPA conjugacy and location can be examined on a case-by-case basis with the new dataset. The results show that at least 73% of TPAs appear in both hemispheres simultaneously. IMF Bₓ and dipole tilt values for conjugate TPAs do not differ from those for non-conjugate TPAs. Most conjugate (isolated) TPAs appear on opposite oval sides in each hemisphere (57%). Interestingly, in case northern and southern hemisphere TPAs form on the same oval side, they appear typically at dawn during weak IMF By.

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Series: Journal of geophysical research. Space physics
ISSN: 2169-9380
ISSN-E: 2169-9402
ISSN-L: 2169-9380
Volume: 128
Issue: 1
Article number: e2022JA030987
DOI: 10.1029/2022JA030987
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Funding: This work has been supported by the Swedish National Space Agency DNR-155A/17.
Copyright information: © 2022 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.