Recordings of geomagnetically induced currents and a nowcasting service of the Finnish natural gas pipeline system

[ 1] The geomagnetically induced currents (GIC) in the Finnish natural gas pipeline have been measured at one site in southern Finland since November 1998. We give an overview of this long and uniform time series covering one sunspot maximum. We also briefly discuss the conventional magnetic activity indices K and Ak, and, additionally, the range of the magnetic field and of its time derivative, as indicators of the GIC activity. The measured GIC data formed the basis of the development of a nowcasting service ( GIC Now!), which was implemented within the European Space Agency Space Weather Applications Pilot Project. The service provides a near-real-time view of the geomagnetic activity level and nowcast estimates of GIC and pipe-to-soil voltages in the Finnish natural gas pipeline system. We describe the operation and validation of this service in this paper.