Magnetic observatories constitute a global network of scientific infrastructure committed to long-term Earth observation according to common standards and open data sharing as well as to societal relevance. Combined with recent geomagnetic satellite missions, the usefulness of ground-based data for modern navigation system and space weather monitoring has been increasingly adding to observatories’ scientific and societal importance.

The special issue Geomagnetic observatories, their data, and the application of their data addresses open research topics related to ground observations of the Earth’s magnetic field, including those based on the presentations given during two recent events: the XIXth IAGA Workshop on Geomagnetic Observatory Instruments, Data Acquisition and Processing (a conference and workshop that was held in Sopron and Tihany, Hungary, from May 22 to 26 in 2023) and the XXth IAGA Workshop on Geomagnetic Observatory Instruments, Data Acquisition and Processing (held in Vassouras, Brazil, from October 30 to November 6 in 2024).

This special issue focuses on magnetic observatory operation, magnetic observation instrumentation, the processing and distribution of geomagnetic observatory data, the application of these data to fundamental and applied science, and the data’s societal relevance. Related subjects, such as geomagnetic variometer stations, and papers that demonstrate a relationship to geomagnetic observatories also fall into the special issue’s scope.

Review process: all papers of this special issue underwent the regular interactive peer-review process of Geoscientific Instrumentation, Methods and Data Systems handled by members of the editorial board as well as guest editors designated by the GI executive editors.