Evaluation of the geometry of ionospheric current systems related to rapid geomagnetic variations

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 (100-1000 nT/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.

Nighttime Magnetic Perturbation Events Observed in Arctic Canada: 1. Survey and Statistical Analysis

“…Viljanen et al (2006) also suggested that the scattering of the directions of the maximum derivatives was related to smaller scale structures such as vortices. This is consistent with the earlier results of Apatenkov et al (2004), who found, using IMAGE magnetometer data from 1996 through 2000, that the majority of the strongest dB/dt events appeared to be produced by vortex-type current structures. This conjecture was also confirmed by Belakhovsky et al (2018), who found a much higher directional variability of the horizontal vector component of dB/dt compared to the horizontal component of ΔB during the magnetic storm of 17 March 2013.…”

The GIC and Geomagnetic Response Over Fennoscandia to the 7–8 September 2017 Geomagnetic Storm

“…What is also apparent is that the largest magnetic depressions do not necessarily result in the largest d Bx /d t values, which appears much more complex. Comparing this interval to the previous one, the ionospheric structures here are more vortex‐like (Apatenkov et al, ; Henderson, ; Henderson et al, ; Viljanen et al, ) and rotational by nature, whereas the behavior during interval [2] manifested as pulsation‐like variations in the EE. It is clear that these observed complex geomagnetic and ionospheric disturbances correlate very well with the d Bx /d t and GIC recordings.…”

Nighttime Magnetic Perturbation Events Observed in Arctic Canada: 2. Multiple‐Instrument Observations

“…The southward perturbations in the H (north‐south) component of the magnetic field at Kotelny, Siberia (69.7 MLAT) shown in their Figure , associated with a ~500 km northward auroral expansion, closely resembled the typical nighttime solitary perturbation events shown in Paper 1. Similarly, Apatenkov et al () and Belakhovsky et al () both noted an association between perturbation events and vortical current structures, and Huttunen et al () found that during the April 2000 magnetic storm geomagnetically induced currents were strongly enhanced during several periods. While some perturbation intervals were associated with substorm onsets or electrojet enhancements, Huttunen et al () found that others were caused by extremely localized and short‐lived electrojet activations.…”