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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: regular paper 21 Aug 2019

Submitted as: regular paper | 21 Aug 2019

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A revised version of this preprint is currently under review for the journal ANGEO.

AMPERE Polar Cap Boundaries

Angeline G. Burrell1, Gareth Chisham2, Stephen E. Milan3, Liam Kilcommons4, Yun-Ju Chen5, Evan G. Thomas6, and Brian Anderson7 Angeline G. Burrell et al.
  • 1U.S. Naval Research Laboratory, 4555 Overlook Ave SW, Washington, DC, USA
  • 2British Antarctic Survey, Cambridge, UK
  • 3University of Leicester, University Road, Leicester, UK
  • 4University of Colorado, Boulder, 2055 Regent Drive, Boulder, CO, USA
  • 5University of Texas at Dallas, 800 West Campbell Road, Richardson, TX, USA
  • 6Dartmouth College, 14 Engineering Drive, Hanover, NH, USA
  • 7Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD, USA

Abstract. The high latitude atmosphere is a dynamic region with processes that respond to forcing from the Sun, magnetosphere, neutral atmosphere, and ionosphere. Historically, the dominance of magnetosphere-ionosphere interactions has motivated upper atmospheric studies to use magnetic coordinates when examining magnetosphere-ionosphere-thermosphere coupling processes. However, there are significant differences between the dominant interactions within the polar cap, auroral oval, and equatorward of the auroral oval. Organising data relative to these boundaries has been shown to improve climatological and statistical studies, but the process of doing so is complicated by the shifting nature of the auroral oval and the difficulty in measuring its poleward and equatorward boundaries.

This study presents a new set of open-closed magnetic field line boundaries (OCBs) obtained from Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) magnetic perturbation data. AMPERE observations of field aligned currents (FACs) are used to determine the location of the boundary between the Region 1 (R1) and Region 2 (R2) FAC systems. This current boundary is thought to typically lie a few degrees equatorward of the OCB, making it a good candidate for obtaining OCB locations. The AMPERE R1/R2 boundaries are compared to the Defense Meteorological Satellites Program Special Sensor J (DMSP SSJ) electron energy flux boundaries to test this hypothesis and determine the best estimate of the systematic offset between the R1/R2 boundary and the OCB as a function of magnetic local time. These calibrated boundaries, as well as OCBs obtained from Magnetopause-to-Aurora Global Exploration (IMAGE) observations, are validated using simultaneous observations of the convection reversal boundary measured by DMSP. The validation shows that the OCBs from IMAGE and AMPERE may be used together in statistical studies, providing the basis of a long-term data set that can be used to separate observations originating inside and outside of the polar cap.

Angeline G. Burrell et al.

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Status: final response (author comments only)
Status: final response (author comments only)
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Angeline G. Burrell et al.

Model code and software

aburrell/ocbpy: Beta Release A. G. Burrell and G. Chisham

lkilcommons/ssj_auroral_boundary: Version 1 L. Kilcommons and A. G. Burrell

Angeline G. Burrell et al.


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Latest update: 21 Feb 2020
Publications Copernicus
Short summary
The Earth's polar upper atmosphere changes along with the magnetic field, other parts of the atmosphere, and the Sun. When studying these changes, knowing the polar region the data comes from is vital, since different processes dominate the area where the aurora are and poleward of the aurora (the polar cap). The boundary between these areas is hard to find, so this study used a different boundary and figured out how they are related. Future studies can now find their polar region more easily.
The Earth's polar upper atmosphere changes along with the magnetic field, other parts of the...