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Abstract

Magnetic Observatories have been in operation in Norway for more than a century. To evaluate magnetic disturbances and to convey these to the scientific community, various magnetic indices have been calculatedand published throughout most of the history. With basis in the work ofKristian Birkeland in the beginning of the 1900s, his Magnetic Storminess index was provided from Norwegian stations during the first half of the century, but was later discontinued in favor of the localK-index. Today Tromsø Geophysical Observatory (TGO) is responsible formagnetic observatory work in Norway, and continues to provide local magnetic indices from several stations. In this work we present the complete, existing data set of K-values from Norwegian observatories at Bear Island, Tromsø and Dombås and the process of identifying published sources and digitizing them, as well as the Magnetic Storminess index. We discuss the continuity of the datasets in the transition between handscaling of analogue magnetograms and automatic calculation from digital data. Different methods for automatic calculation including simplifications and assumptions, used at TGO, is discussed and compared. Furthermore, observatory specific oddities and qualities int he K-indices and the spectra of K-index derived Ak, are discussed. In order to extend the K-derived time series even further backwards in time than what is published, we discuss the similarity and difference between Magnetic Storminess and K and establish relationships between the two. We then, finally, present an extended Ak time series for Tromsø and Dombås.