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  Evolution of Large‐Scale Magnetic Fields From Near‐Earth Space During the Last 11 Solar Cycles

Pick, L., Korte, M., Thomas, Y., Krivova, N. A., & Wu, C.-J. (2019). Evolution of Large‐Scale Magnetic Fields From Near‐Earth Space During the Last 11 Solar Cycles. Journal of Geophysical Research: Space Physics, 124(4), 2527-2540. doi:10.1029/2018JA026185.

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Item Permalink: http://hdl.handle.net/21.11116/0000-0006-67F4-3 Version Permalink: http://hdl.handle.net/21.11116/0000-0006-67F5-2
Genre: Journal Article

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 Creators:
Pick, Leonie, Author
Korte, Monika, Author
Thomas, Yannik, Author
Krivova, Natalie A.1, Author              
Wu, Chi-Ju1, Author              
Affiliations:
1Department Sun and Heliosphere, Max Planck Institute for Solar System Research, Max Planck Society, ou_1832289              

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 Abstract: We use hourly mean magnetic field measurements from 34 midlatitude geomagnetic observatories between 1900 and 2015 to investigate the long-term evolution and driving mechanism of the large-scale external magnetic field at ground. The Hourly Magnetospheric Currents index (HMC) is derived as a refinement of the Annual Magnetospheric Currents index (HMC, Pick & Korte, 2017, https://doi.org/10.1093/gji/ggx367). HMC requires an extensive revision of the observatory hourly means. It depends on three third party geomagnetic field models used to eliminate the core, the crustal, and the ionospheric solar-quiet field contributions. We mitigate the dependency of HMC on the core field model by subtracting only nondipolar components of the model from the data. The separation of the residual (dipolar) signal into internal and external (HMC) parts is the main methodological challenge. Observatory crustal biases are updated with respect to AMC, and the solar-quiet field estimation is extended to the past based on a reconstruction of solar radio flux (F10.7). We find that HMC has more power at low frequencies (periods ≥ 1 year) than the Dcx index, especially at periods relevant to the solar cycle. Most of the slow variations in HMC can be explained by the open solar magnetic flux. There is a weakly decreasing linear trend in absolute HMC from 1900 to present, which depends sensitively on the data rejection criteria at early years. HMC is well suited for studying long-term variations of the geomagnetic field. ©2019. American Geophysical Union. All Rights Reserved.

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Language(s): eng - English
 Dates: 2019
 Publication Status: Published in print
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.1029/2018JA026185
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Title: Journal of Geophysical Research: Space Physics
  Other : JGR-A
  Abbreviation : J. Geophys. Res. - A
Source Genre: Journal
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Publ. Info: Washington, D.C. : American Geophysical Union
Pages: - Volume / Issue: 124 (4) Sequence Number: - Start / End Page: 2527 - 2540 Identifier: ISSN: 0148-0227
CoNE: https://pure.mpg.de/cone/journals/resource/991042728714264