© Author(s) 2009. This work is distributed
under the Creative Commons Attribution 3.0 License.
Characteristics of variations in the ground magnetic field during substorms at mid latitudes
1Department of Communication Systems, InfoLab21, Lancaster University, Lancaster, LA1 4WA, UK
2British Geological Survey, West Mains Road, Edinburgh, EH9 3LA, UK
*now at: Petroleum Geoservices, 10 Bankhead Crossway South, Edinburgh, EH11 4EP, UK
Abstract. Substorms are known to cause geomagnetically induced currents (GIC) in power transmission lines through variations in the ground magnetic field. An improved knowledge and understanding of how the different phases of substorms affect the ground magnetic field will ultimately help to better understand how GIC arise. Although usually associated with high latitude power transmission networks, GIC potentially pose a risk to mid latitude networks such as the UK's National Grid. Using a list of substorm expansion phase onsets derived from auroral observations by the IMAGE-FUV satellite, this study examines 553 individual onsets. In order to cover mid latitudes, ground magnetometer data from the UK Sub-Auroral Magnetometer Network (SAMNET) are exploited. These high time resolution (5 s) data are used to study the ground magnetic field for an hour after onset, in particular the time derivative of the horizontal magnetic field, H. The data covers the period from 2000 to 2003 (just after solar maximum). Results are compared with a previous study of magnetic field variations at higher latitudes, using data with a much lower (1 min) cadence during substorms identified from geomagnetic indices during a period just after solar minimum.