ANGEO Annales Geophysicae ANGEO 1432-0576 Copernicus GmbH Göttingen, Germany 10.5194/angeo-27-3421-2009 Characteristics of variations in the ground magnetic field during substorms at mid latitudes Turnbull K. L. 1 Wild J. A. 1 Honary F. 1 Thomson A. W. P. 2 McKay A. J. 2 3 Department of Communication Systems, InfoLab21, Lancaster University, Lancaster, LA1 4WA, UK British Geological Survey, West Mains Road, Edinburgh, EH9 3LA, UK now at: Petroleum Geoservices, 10 Bankhead Crossway South, Edinburgh, EH11 4EP, UK 01 09 2009 27 9 3421 3428 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.ann-geophys.net/27/3421/2009/angeo-27-3421-2009.html The full text article is available as a PDF file from http://www.ann-geophys.net/27/3421/2009/angeo-27-3421-2009.pdf

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, <I><B>H</B></I>. 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.

 References Baumjohann, W., Kamide, Y., and Nakamura, R.: Substorms, Storms, and the Near Earth Tail, J. Geomag. Geoelectr., 48, 117–185, 1996. Bolduc, L.: GIC observations and studies in the Hydro-Québec power system, J. Atmos. Terr. Phys., 64, 1793–1802, 2002. Boteler, D H.: Geomagnetically Induced Currents: Present knowledge and future research., IEE Transactions on Power Delivery, 9, 1994. Cowley, S. W H., Davies, J A., Grocott, A., Khan, H., Lester, M., McWilliams, K A., Milan, S E., Provan, G., Sandholt, P E., Wild, J A., and Yeoman, T K.: Solar wind-magnetosphere-ionosphere interactions in the Earth's plasma environment., Phil. Trans. A, 361, 113–126, 2003. Erinmez, I A., Kappenman, J G., and Radasky, W A.: Management of the geomagnetically induced current risks on the national grid company's electric power transmission system, J. Atmos.Terr. Phys., 64, 743–756, 2002. Frey, H U., Mende, S B., and Angelopoulos, V.: Substorm onset observations by IMAGE-FUV, J. Geophys. Res., 109, A10304, \doi10.1029/2004JA010607, 2004. Gaunt, C T. and Coetzee, G.: Transformer failures in regions incorrectly considered to have low GIC-risk., IEEE Power Tech, Conference Paper 445, 2007. Kappenman, J G.: An overview of the impulsive geomagnetic field disturbances and power grid impacts associated with the violent Sun-Earth connection events of 29–31 October 2003 and a comparative evaluation with other contemporary storms., Space Weather, 3, SO8C01, \doi10.1029/2004SW000128, 2005. Kappenman, J G.: Geomagnetic Disturbances and Impacts upon Power System Operation, The Electric Power Engineering Handbook, edited by: Gigsby, L. L., CRC Press/IEEE Press, 2nd edn., 2007. Koen, J.: Geomagnetically induced currents and their pressence in the Southern African electricity transmission network., PhD thesis, University of Cape Town, 2002. Lehtinen, M. and Pirjola, R.: Currents produced in earthed conductor networks by geomagnetically-induced electric fields, Ann Geophys., 4, 479–484, 1985. Molinski, T S.: Why utilities respect geomagnetically induced currents, J. Atmos. Terr. Phys., 64, 1765–1778, 2002. NGDC: ftp://ftp.ngdc.noaa.gov/STP/GEOMAGNETIC_DATA/INDICES/DST/, last access 6 March 2009. Ngwira, C M., Pulkkinen, A., McKinnell, L.-A., and Cilliers, P J.: Improved modeling of geomagnetically induced currents in the South African power network, Space Weather, 40, S11004, \doi10.1029/2008SW000408, 2008. Rae, I J., Mann, I R., Murphy, K R., Milling, D K., Parent, A., Angelopoulous, V., Frey, H U., Kale, A., Watt, C. . E J., Mende, S B., and Russell, C T.: Timing and localization of ionospheric signatures associated with substorm expansion phase onset., J. Geophys. Res., 114, A00C09, \doi10.1029/2008JA013559, 2009. Thomson, A. W P., McKay, A J., Clarke, E., and Reay, S J.: Surface electric fields and geomagnetically induced currents in the Scottish Power grid during the 30 October 2003 geomagnetic storm, Space Weather, 3, S11002, \doi10.1029/2005SW000156, 2005. Viljanen, A., Nevanlinna, H., Pajunpää, K., and Pulkkinen, A.: Time derivative of the horizontal geomagnetic field as an activity indicator, Ann. Geophys., 19, 1107–1118, 2001. Viljanen, A., Tanskanen, E. I., and Pulkkinen, A.: Relation between substorm characteristics and rapid temporal variations of the ground magnetic field, Ann. Geophys., 24, 725–733, 2006. Wik, M., Viljanen, A., Pirjola, R., Pulkkinen, A., Wintoft, P., and Lundstedt, H.: Calculation of geomagnetically induced currents in the 400 kV power grid in southern Sweden, Space Weather, 6, S07005, \doi10.1029/2007SW000343, 2008.