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AMPERE polar cap boundaries

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journal contribution
posted on 2020-04-30, 08:50 authored by AG Burrell, G Chisham, SE Milan, L Kilcommons, YJ Chen, EG Thomas, B Anderson
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 Satellite 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 the Imager for 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.

Funding

This research has been supported by the United States Chief of Naval Research (US CNR); the United Kingdom Research and Innovation (UKRI), British Antarctic Survey – Polar Science for Planet Earth Programme; the Air Force Office of Scientific Research (grant nos. FA9550-17-1-0258 and FA9559-16-1-0364); and the National Science Foundation, Office of Polar Programs (grant no. OPP-1836426).

History

Citation

Burrell, A. G., Chisham, G., Milan, S. E., Kilcommons, L., Chen, Y.-J., Thomas, E. G., and Anderson, B.: AMPERE polar cap boundaries, Ann. Geophys., 38, 481–490, https://doi.org/10.5194/angeo-38-481-2020, 2020.

Version

  • VoR (Version of Record)

Published in

Annales Geophysicae

Volume

38

Issue

2

Pagination

481 - 490

Publisher

Copernicus GmbH

issn

0992-7689

eissn

1432-0576

Acceptance date

2020-03-11

Copyright date

2020

Available date

2020-04-08

Publisher version

https://www.ann-geophys.net/38/481/2020/

Language

en

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