Annales Geophysicae
Annales Geophysicae
ANGEO
Articles | Volume 43, issue 1
Articles | Volume 43, issue 1
https://doi.org/10.5194/angeo-43-241-2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/angeo-43-241-2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
Articles | Volume 43, issue 1
Regular paper
 | 
20 May 2025
Regular paper |  | 20 May 2025

A critical review and presentation of the complete, historic series of K indices as determined at Norwegian magnetic observatories since 1939

Ingeborg Frøystein and Magnar Gullikstad Johnsen

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Short summary
The complete time series of the geomagnetic disturbance index (K) from Norwegian magnetic observatories have been digitized. We compare and discuss the tree methods used to derive the index, finding that each method has strengths and weaknesses. In total, we present all K indices derived from Norwegian observatories since the 1930s until today, the used derivation methods and the long historic time series as a whole, enabling critical use for future scientific work.
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