Abstract
Abstract. To learn about the geometry and sources of the ionospheric current systems which generate strong geomagnetically induced currents, we categorize differential equivalent current systems (DEC) for events with strong dB/dt by decomposing them into the contributions of electrojet-type and vortex-type elementary systems. By solving the inverse problem we obtain amplitudes and locations of these elementary current systems. One-minute differences of the geomagnetic field values at the IMAGE magnetometer network in 1996–2000 are analysed to study the spatial distributions of large dB/dt events. The relative contributions of the two components are evaluated. In particular, we found that the majority of the strongest dB/dt events (100–1000nT/min) appear to be produced by the vortex-type current structures and most of them occur in the morning LT hours, probably caused by the Ps6 pulsation events associated with auroral omega structures. For strong dB/dt events the solar wind parameters are shifted toward strong (tens nT) southward IMF, enhanced velocity and dynamic pressure, in order for the main phase of the magnetic storms to occur. Although these events appear mostly during magnetic storms when the auroral oval greatly expands, the area of large dB/dt stays in the middle part of the auroral zone; therefore, it is connected to the processes taking part in the middle of the magnetosphere rather than in its innermost region populated by the ring current. Key words. Geomagnetism and paleomagnetism (rapid time variations) – Ionosphere (auroral ionosphere; ionospheric disturbances)
Highlights
Induced currents (GIC) in long conductor systems, like power transmission systems or pipelines, are caused by rapid changes in the Earth’s magnetic field (e.g.Boteler et al, 1998; Viljanen and Pirjola, 1994)
In this paper we address the question of how often is the simple auroral electrojets (AEJ) model adequate for Geomagnetically induced currents (GIC) modeling, and, how large can the contribution from non-onedimensional systems can be during large dB/dt events
Our results indicate a large contribution from vortex currents to the equivalent current systems, that produce large dB/dt and, potentially, large GIC effects
Summary
Induced currents (GIC) in long conductor systems, like power transmission systems or pipelines, are caused by rapid changes in the Earth’s magnetic field In this paper we address the question of how often is the simple AEJ model adequate for GIC modeling, and, how large can the contribution from non-onedimensional systems can be during large dB/dt events To characterize it in a quantitative way, we represent the equivalent currents as a sum of the simplest 1-D (AEJ) and 2-D (vortex) contributions, which allows us to evaluate their relative contributions to magnetic variations observed on the dense IMAGE magnetometer network. With this simple tool we analyse the large dB/dt events observed during the rising phase of the solar cycle (years 1996–2000), and study statistically the spatial distributions and solar wind conditions, paying attention to the relative complexity of the current system. We do not expect to miss intensifications of such current systems
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