Lead Applicant International Union on Geodesy and Geophysics Supporting Applicant ICSU Panel on World Data Centers Principal Investigator

Routine observations of the Earth’s magnetic field variations began in early 1800s in London and Paris. At that time, an observer visually detected deviations of a compass needle and recorded this manu-ally in a notebook; an automatic recording system was invented only in 1840s. Therefore, by now more than 160 years of geomagnetic field observations recorded in various locations mainly by analogue scien-tific instruments are in possession of the World Data Centers and various government agencies or scien-tific institutions. These time series are extremely important for studying secular and long-term variations of the main geomagnetic field, as well as for determining the character of short-term field variations over almost two centuries. The latter is important for better understanding of long trends in the solar activity and its forcing to the Earth’s atmosphere and climatic changes. A most long-time series of geomagnetic aa index exists since 1868; this index has been utilized in many analyses of geomagnetic activity over thirteen 11-year-long solar activity cycles. Lockwood et al. [1999] have used the aa index to show that geomagnetic activity gradually increases since 1900s. How-ever even having the long-time index series, scientists need daily magnetograms recorded at certain mag-netic observatories to check some historical geomagnetic events or simply to compare the geomagnetic activity levels nowadays and in the past. For example, geomagnetic storms are important because of grea