The WDC is holding extensive archives of magnetograms and other geomagnetic observatory data products that predate the introduction of digital data recording. The material is in analogue form such as film or microfiche.
Catalogues (pdf) of the WDC Copenhagen analogue data archive
Additionally, the WDC has an ftp-server to distributes the Northern PC index (description) derived from the geomagnetic observatory Qaanaaq (THL) and the Kp-index data products derived at the geomagnetic observatory Niemegk (NGK).
The WDC Copenhagen was established for the International Geophysical Year in 1957 at the Danish Meteorological Institute. The Geomagnetic Data Master Catalogue of hourly and 1-minute means of the geomagnetic observatories was developed at WDC Copenhagen and moved to WDC Edinburgh in 2007.
The WDC Copenhagen is maintained by DTU Space from 2010 onwards. More information on the WDC System is provided by NGDC/NOAA.