Abstract
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.
Highlights
Substorms are rapid reconfigurations of the terrestrial magnetosphere resulting from the release of solar wind energy and momentum stored in the Earth’s magnetospheric tail
The plot shows that average max|dH /dt| increases with latitude for storm time and non-storm time substorm onsets
This study focuses on the time derivative of the horizontal ground magnetic field as this is the key value when considering the generation of geomagnetically induced currents (GIC) from substorms (Viljanen et al, 2001)
Summary
Substorms are rapid reconfigurations of the terrestrial magnetosphere resulting from the release of solar wind energy and momentum stored in the Earth’s magnetospheric tail. This energy is primarily transferred into the magnetosphere from the interplanetary magnetic field (IMF) and solar wind via magnetic reconnection at the dayside magnetopause. Magnetic flux is added to the tail lobes causing the magnetic flux density in the tail to increase. This stored energy is eventually released in an explosive fashion and the magnetosphere undergoes rapid reconfiguration. Substorms can occur at anytime but are observed more frequently during high solar activity (Baumjohann et al, 1996)
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