Relation between substorm characteristics and rapid temporal variations of the ground magnetic field

• Published in: Annales geophysicae (1988) Vol. 24; no. 2; pp. 725 - 733
• Main Authors: VILJANEN, A, TANSKANEN, E. I, PULKKINEN, A
• Format: Journal Article
• Language: English
• Published: Katlenburg-Lindau European Geophysical Society 23.03.2006; European Geosciences Union; Copernicus Publications
• Subjects: Earth Sciences; Earth, ocean, space; Exact sciences and technology; External geophysics; Ocean, Atmosphere; Physics of the high neutral atmosphere; Physics of the ionosphere; Physics of the magnetosphere; Sciences of the Universe; Magnetospheric physics (Storms and substorms); magnetic field; time variations; Ionosphere (Auroral ionosphere); Equivalent current; Auroral substorm; Fast variation; Polar ionosphere; Ionospheric current; sunspots; Geomagnetism and paleomagnetism (Rapid time variations); Vector field; Westward electrojet
• ISSN: 0992-7689; 1432-0576; 1432-0576
• DOI: 10.5194/angeo-24-725-2006

Auroral substorms are one of the major causes of large geomagnetically induced currents (GIC) in technological systems. This study deals with different phases of the auroral substorm concerning their severity from the GIC viewpoint. Our database consists of 833 substorms observed by the IMAGE magnetometer network in 1997 (around sunspot minimum) and 1999 (rising phase of the sunspot cycle), divided into two classes according to the Dst index: non-storm (Dst>-40 nT, 696 events) and storm-time ones (Dst<-40 nT, 137 events). The key quantity concerning GIC is the time derivative of the horizontal magnetic field vector (dH/dt) whose largest values during substorms occur most probably at about 5 min after the onset at stations with CGM latitude less than 72 deg. When looking at the median time of the occurrence of the maximum dH/dt after the expansion onset, it increases as a function of latitude from about 15 min at CGM lat=56 deg to about 45 min at CGM lat=75 deg for non-storm substorms. For storm-time events, these times are about 5 min longer. Based on calculated ionospheric equivalent currents, large dH/dt occur mostly during the substorm onset when the amplitude of the westward electrojet increases rapidly.