Sensitivity of ground magnetometer array elements for GIC applications
I: Resolving spatial scales with the BEAR and CARISMA arrays
Abstract
Geomagnetically induced currents (GICs) can be driven in terrestrial
electrical power grids as a result of the induced electric fields
arising from geomagnetic disturbances (GMD) resulting from the dynamics
of the coupled magnetosphere-ionosphere-ground system. However, a key
issue is to assess an optimum spacing for the magnetometer stations in
order to provide appropriate monitoring of the GIC-related GMD. Here we
assess the vector correlation lengths of GMD and related amplitude
occurrence distribution of the variations of horizontal magnetic field
$dB_{H}/dt$. Specifically, we study the GMD response to two
storm-time substorms using data from two magnetometer arrays, the Baltic
Electromagnetic Array Research (BEAR) Project in Scandinavia and the
Canadian Array for Realtime Investigations of Magnetic Activity
(CARISMA) array in North America, so as to determine the optimal
magnetometer spacing in latitude and longitude, for monitoring and
assessing GIC risk. We find that although magnetic disturbances are
well-correlated up to distances of several hundred kilometers at
mid-latitudes, the vector correlation length rapidly drops off for
station separations of less than 100 km within the auroral oval. In
general geomagnetic fluctuations are stronger and more localized in the
auroral zone. Since the auroral oval is pushed equatorward during
intense magnetic storms, we highlight that networks using a station
separation of $\sim 200$ km should provide an excellent
basis for monitoring both small and large scale geomagnetic
disturbances. A monitoring network with this station spacing is
recommended as being optimal for assessing the role of GMD in driving
GICs in the electric power grid.