Seasonal and Temporal Variations of Field‐Aligned Currents and Ground Magnetic Deflections During Substorms

Forsyth, C.; Shortt, Madeline; Coxon, J. C.; Rae, I. J.; Freeman, M. P.; Kalmoni, N. M. E.; Jackman, C. M.; Anderson, B. J.; Milan, S. E.; Burrell, A. G.

doi:10.1002/2017ja025136

Cited by 24 publications

(30 citation statements)

References 111 publications

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“…The delay between driving and the nightside onset is on the order of 30 min. The nightside onsets correspond to enhancements in AE, consistent with substorm onsets, and the Birkeland currents are consistent with event analyses of substorm currents using AMPERE (L. Clausen et al, ; L. B. N. Clausen et al, ; Connors et al, ; Coxon et al, ; Coxon et al, ; Forsyth et al, ; McPherron et al, ; Murphy et al, ). The onsets are preceded by a southward turning of the IMF that coincides with the dayside currents.…”

Section: Discussionsupporting

confidence: 73%

“…Other studies specifically focused on the development of Birkeland currents with subtorms (cf. Coxon et al, ; Forsyth et al, ; McPherron et al, ) and have shown that auroral substorms closely correlate with intensifications of the nightside R1 and R2 Birkeland currents. Our purpose is to understand the sequence in the development of the global Birkeland current system from a substantial period of quiescence so this analysis is distinct though related to these studies of auroral substorms.…”

Section: Introductionmentioning

confidence: 98%

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Temporal and Spatial Development of Global Birkeland Currents

et al. 2018

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The development of large-scale Birkeland currents is examined using the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE), which measures global Birkeland currents continuously on 10-min time scales. The integrated current was used to identify onsets of at least 1 MA preceded by periods of quiescence lasting at least 3 hr. The Region 1 currents do not fully form without Region 2. Rather, they develop together, first on the dayside, then on the nightside, and lastly, they fill in and intensify at all local times to form the nominal statistical pattern. The onsets are closely correlated with enhancements of magnetospheric forcing as indicated by the solar wind electric field and the orientation of the interplanetary magnetic field. Nightside onsets correspond to intensifications of the auroral electrojet as reflected in the AE index; they are delayed by~40 min relative to the increase of the dayside current and are 2.8 times more rapid than the dayside current increase. After nightside onset, Birkeland currents expand toward dawn and dusk and merge with the dayside currents while also intensifying at all local times. The dayside current pattern depends on the sign of the interplanetary magnetic field B Y . The nightside current distributions are the same for positive and negative B Y and display a Harang discontinuity independent of the sign of B Y . The predominant development and intensification of Birkeland currents occur after nightside onset at all local times with roughly 75% of the total current, both Regions 1 and 2, appearing after nightside onset.Plain Language Summary This study uses data from the 66 Iridium Communications satellites to track the development of electric currents that drive aurora. These currents can turn on in less than about an hour. However, the currents can only be measured from satellites orbiting the Earth above the atmosphere, and in those orbits, satellites take about 100 min to orbit the Earth. With the Iridium constellation, we remeasure these currents every 10 min and are able to track where they start and how they grow. This happens in two steps: Currents appear first in the day where they remain. About 30 min later, new currents start near midnight and then spread toward dawn and dusk and increase until they completely encircle the poles in an oval pattern. The total current finally reaches millions of Amperes. The two-step process implies that explosive dynamics in the magnetic tail of the Earth play a key role in creating and generating the auroral currents. This study shows that the effects they have on the temporal sequence of activity onset need to be included to predict the effects of the solar wind and solar storms on the Earth's ionosphere and upper atmosphere.

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Section: Discussionsupporting

confidence: 73%

Section: Introductionmentioning

confidence: 98%

Temporal and Spatial Development of Global Birkeland Currents

et al. 2018

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“…Since auroral hiss is caused by the Cherenkov radiation of low-energy precipitating electrons, we considered the behavior of the upward field-aligned currents (FACs), also known as Birkeland currents, corresponding to soft electron precipitation. Some upward current increase prior to substorm onset was found by Forsyth et al (2018).…”

Section: 1029/2019gl086285mentioning

confidence: 94%

Ground‐Based Auroral Hiss Recorded in Northern Finland with Reference to Magnetic Substorms

Manninen¹,

Клейменова

Kozlovsky³

et al. 2020

Geophysical Research Letters

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Very low frequency (VLF) auroral hiss at Kannuslehto (KAN), Finland, was analyzed with reference to the progress of 98 isolated magnetic substorms measured during the winter months of 2015–2018. Of these, 91 were accompanied by auroral hiss during the substorm growth phase. No auroral hiss was recorded during the expansion and recovery phases. We found that auroral hiss was observed under rising polar cap (PC) index, showing an increased solar wind energy input into the magnetosphere during the substorm growth phase. We also found that in 58 of the 65 events studied, KAN was located in the vicinity of enhanced field‐aligned currents (FACs) during auroral hiss occurrence. For the first time, it was established that auroral VLF hiss generation in the equatorial part of the auroral oval is a typical signature of a substorm growth phase.

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“…Following a southward turning of the IMF, the Region 1 FACs are enhanced and become stronger than the Region 2 FACs, and penetration electric fields occur at low latitudes (Nopper & Carovillano, 1978;Senior & Blanc, 1984). Similarly, following a substorm onset, the increase of the Region 1 FACs is larger than the increase of the Region 2 FACs (Forsyth et al, 2018), and penetration electric fields are observed at low latitudes (Huang, 2009(Huang, , 2012.…”

Section: Discussionmentioning

confidence: 98%

Systematical Analyses of Global Ionospheric Disturbance Current Systems Caused by Multiple Processes: Penetration Electric Fields, Solar Wind Pressure Impulses, Magnetospheric Substorms, and ULF Waves

Huang

2020

JGR Space Physics

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We present the first systematic analysis of global ionospheric disturbance current systems caused by multiple processes of solar and magnetospheric origin, including reorientations of the interplanetary magnetic field (IMF), sudden changes in the solar wind dynamic pressure, magnetospheric sawtooth substorms, and ultralow frequency (ULF) waves. Measurements from global magnetometer networks are used to derive the equivalent disturbance currents from the polar cap to the equator. A surprising result is that the equivalent disturbance current systems are very similar, although the driving processes are completely different. The equivalent disturbance current system in response to IMF reorientation or substorm onset is characterized by a large vortex on the dayside and evening sector and a smaller vortex near dawn, and the polarity of the current vortices depends on the IMF direction. The equivalent disturbance current system caused by a sudden change in the solar wind pressure or by ULF waves consists of a single vortex at middle and low latitudes and a very small vortex above~60°magnetic latitude near dawn. The similar disturbance current systems caused by different solar wind and magnetospheric processes suggest that the global distribution of the ionospheric currents is determined by the intrinsic property of the ionosphere. The global current system takes only~1 min to completely reconstruct, indicating that the current system can reach a new steady state within 1 min. A scenario is proposed to explain the global distribution and fast reconstruction of the current systems. Penetration electric fields caused by IMF southward turning were first identified by Nishida (1968a, 1968b). It was found that quasiperiodic southward turnings of the IMF with a period of 30-60 min caused quasiperiodic enhancements in the northward component of the geomagnetic field measured by ground magnetometers near the magnetic equator. Because variations of the geomagnetic field are related to variations of ionospheric currents and electric fields, Nishida suggested that a southward turning of the IMF caused the Published 2020. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

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Seasonal and Temporal Variations of Field‐Aligned Currents and Ground Magnetic Deflections During Substorms

Cited by 24 publications

References 111 publications

Temporal and Spatial Development of Global Birkeland Currents

Temporal and Spatial Development of Global Birkeland Currents

Ground‐Based Auroral Hiss Recorded in Northern Finland with Reference to Magnetic Substorms

Systematical Analyses of Global Ionospheric Disturbance Current Systems Caused by Multiple Processes: Penetration Electric Fields, Solar Wind Pressure Impulses, Magnetospheric Substorms, and ULF Waves

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