Geophysical Institute of the ASCR

) The rapidly varying geomagnetic field occurring in connection with geomagnetic storms may
induce electric fields and currents that can affect technological systems such as power transmission
grids, telecommunication cables and oil or gas pipelines. Geomagnetically induced currents
(GIC’s) are a source of problems for technological systems mainly at high geomagnetic latitudes.
That is why these phenomena have been studied intensively in Canada, Scandinavia and Scotland.
Nevertheless, strong geomagnetic disturbances can have quite strong effects even at mid-latitudes.
Irregular currents observed in the oil pipelines in the Czech Republic during the Halloween
magnetic storms in October 2003 caused that the pipeline operator contacted the geomagnetic
department of the Geophysical Institute.
In the frame of a pilot study (Hejda and Bochníček, 2005), data from three measuring stations
were analysed and compared with the geomagnetic field registered at the Budkov observatory
(Fig. 37). It was shown that the simplest – plane wave and uniform Earth – model of the
geoelectric field corresponds well to the measured pipe-to soil voltage. Although the largest
amplitudes of the geomagnetic field were reached on the onset of the geomagnetic storm, largest
voltages were also induced in the main and recovery phase due to Pc5 oscillations.
c) The quality of magnetic surveys is essentially influenced by the geomagnetic activity. As the in
situ measurements are usually limited to a very short time period, they must be compared with
observatory continuous registrations. When reducing measurements one makes an assumption that
diurnal variations of the magnetic field are identical at both the station and the reference
observatory. During magnetically quiet periods, this assumption is satisfied to an acceptable
extent. However, under high geomagnetic activity, the error may easily exceed the acceptable limit.
Analysis made by Hejda et al. (2005) indicates that, in mid-latitudes, magnetic surveys should not
be made, if some of the Kp values are over 5. Basic periodicities of the geomagnetic activity (11-
year, half-year and 27-day) should be considered by long-term and medium-term planning of
magnetic survey. Short-term forecasts, which are distributed in the frame of Regional Warning
Center network, can provide useful information for a few next days.
References
Bochníček J., Hejda P., 2005. The winter NAO pattern changes in association with solar and geomagnetic activity. Journal of
Atmospheric and Solar-Terrestrial Physics, 67, 17-32.
Hejda, P., Bochníček, J., 2006. Geomagnetically induced pipe-to-soil voltages in the Czech oil pipelines during October-
November 2003, Annales geophysicae, in print.
Hejda P., Bochníček J., Horáček J., Nejedlá J., 2006. Time scheduling of magnetic surveys in mid-latitudes with respect to
forecasting geomagnetic activity. Earth, Planets and Space, in print.
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