Abstract
AbstractRapid changes of magnetic fields associated with nighttime magnetic perturbation events (MPEs) with amplitudes |ΔB| of hundreds of nT and 5–10 min duration can induce geomagnetically induced currents (GICs) that can harm technological systems. This study compares the occurrence and amplitude of nighttime MPEs with |dB/dt| ≥ 6 nT/s observed during 2015 and 2017 at five stations in Arctic Canada ranging from 64.7° to 75.2° in corrected geomagnetic latitude (MLAT) as functions of magnetic local time (MLT), the SME (SuperMAG version of AE) and SYM/H magnetic indices, and time delay after substorm onsets. Although most MPEs occurred within 30 min after a substorm onset, ∼10% of those observed at the four lower latitude stations occurred over two hours after the most recent onset. A broad distribution in local time appeared at all five stations between 1700 and 0100 MLT, and a narrower distribution appeared at the lower latitude stations between 0200 and 0700 MLT. There was little or no correlation between MPE amplitude and the SYM/H index; most MPEs at all stations occurred for SYM/H values between −40 and 0 nT. SME index values for MPEs observed >1 h after the most recent substorm onset fell in the lower half of the range of SME values for events during substorms, and dipolarizations in synchronous orbit at GOES 13 during these events were weaker or more often nonexistent. These observations suggest that substorms are neither necessary nor sufficient to cause MPEs, and hence predictions of GICs cannot focus solely on substorms.
Highlights
Evidence of the impact of solar disturbances on technological systems on Earth arguably goes back to the Carrington event of 1859 (Carrington, 1860), in which a large and complex set of solar flares caused disturbances in telegraph systems over a large portion of the Earth, the developing scientific understanding of the connection between “space weather” and its impacts on human technological systems is still incomplete
This study compares the occurrence and amplitude of nighttime magnetic perturbation events (MPEs) with |dB/dt| ≥ 6 nT/s observed during 2015 and 2017 at five stations in Arctic Canada ranging from 64.7° to 75.2° in corrected geomagnetic latitude (MLAT) as functions of magnetic local time (MLT), the SME (SuperMAG version of AE) and SYM/H magnetic indices, and time delay after substorm onsets
We considered the effect of multiple prior substorm onsets separately for MPEs in the two populations shown in Figure 4a: the “premidnight” population observed between 1700 and 0100 MLT, and the “postmidnight” population observed between 0200 and 0700 MLT
Summary
Evidence of the impact of solar disturbances on technological systems on Earth arguably goes back to the Carrington event of 1859 (Carrington, 1860), in which a large and complex set of solar flares caused disturbances in telegraph systems over a large portion of the Earth, the developing scientific understanding of the connection between “space weather” and its impacts on human technological systems is still incomplete. Recent observational studies by Ngwira et al (2015, 2018), Belakhovsky et al (2019), Dimmock et al (2019, 2020), and Apatenkov et al (2020) have provided new evidence of the localized nature of the magnetospheric and/or ionospheric processes associated with these impulsive magnetic perturbations. This paper found that conjugate premidnight MPEs were often but not always simultaneous to within 3 min over ∼100–700 km in latitude, while postmidnight MPEs associated with an omega band were very localized and independent in time Analysis of these events showed that both perturbation amplitudes and maximum derivatives favored a current generator model over a voltage generator model for near-solstice events.
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