Our new paper was accepted for publication in A&A journal
We analysed full-disc observations of the Sun in the Hα line (656.28nm) sampling the solar chromosphere and provide information on filament regions.
aanda.org/component/arti…

Filaments are dark elongated regions seen in the solar chromosphere at locations where the magnetic field changes polarity. Thus having information about the location of filaments allows to trace the changes of solar magnetic field in the past, when direct data do not exist.

In this work we used data from 15 observatories covering the period 1909 to 2022. We were thus able to map filament locations and areas for more than 100 years as seen in this butterfly (time/latitude) diagram where we compile all data together.

Furthermore, by studying image characteristics we were able to identify sources of inconsistencies in the archives. This has important implications also for reconstructions of past irradiance variations from Ca II K data from these archives.
aanda.org/articles/aa/ab…

The article is the result of international collaboration with researchers from the observatories in Paris (France), Coimbra (Portugal), Rome (Italy), Catania (Italy), Kharkiv (Ukraine), Larissa (Greece), Tokyo (Japan) as well as ARIES & Max Planck Institute for Solar System Research research institutes