Substorm Occurrence and Intensity Associated With Three Types of Solar Wind Structure

Liou, K.; Sotirelis, T.; Richardson, I. G.

doi:10.1002/2017ja024451

Cited by 20 publications

(16 citation statements)

References 71 publications

(94 reference statements)

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“…Some other studies suggest that some substorms are partly triggered and some are not (Hsu & McPherron, 2003). This viewpoint is supported by the work of Liou et al (2018), who inspected substorm wait time and intensity and found bimodal distributions. They interpreted the bimodal distributions as evidence of coexistence of external and internal trigger.…”

Section: Introductionmentioning

confidence: 70%

Control of the East‐West Component of the Interplanetary Magnetic Field on the Occurrence of Magnetic Substorms

Liou

Sotirelis

Mitchell

2020

Geophysical Research Letters

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We study the effects of the east‐west (y) component of the interplanetary magnetic field (IMF) on the occurrence of substorms by analyzing 16,743 magnetic substorm events identified with the SuperMAG SML index from 1995 to 2016. It is found, surprisingly, that substorm occurrence rates depend highly on the sign of IMF By, with, on average, ~1/3 more substorms for IMF By > 0 than for IMF By < 0. We attribute this asymmetry to the enhanced convection (e.g., more energy in the tail) under IMF By > 0 conditions. A superposed epoch analysis of the IMF indicates that the average IMF By prior to onset is positive but becomes less positive ~15 min prior to the onset, indicating that the release of the stress associated with a clockwise twisted magnetotail may be an important onset trigger. We conjecture that an asymmetry in the dayside merging efficiency may be the cause.

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Section: Introductionmentioning

confidence: 70%

Control of the East‐West Component of the Interplanetary Magnetic Field on the Occurrence of Magnetic Substorms

Liou

Sotirelis

Mitchell

2020

Geophysical Research Letters

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“…We believe it is interesting to see how our results using high-resolution auroral observations compare with previous results that did not directly use such observations. In particular, we compare to the idea based partially on particle injections that substorms might repeat with an ~ 2–4 h period (referred to as “sawtooth events”) during storms that are driven by moderate to strong (Bz ≲ − 10 nT) and continuously southward IMF conditions (Henderson et al 2006, and references therein) and to the recent evaluation indicating that substorm occurrence rates might be similar during CME and HSS storms (Liou et al 2017). We also compare to apparently conflicting proposals.…”

Section: Introductionmentioning

confidence: 98%

Stormtime substorm onsets: occurrence and flow channel triggering

Lyons

Zou

Nishimura

et al. 2018

Earth Planets Space

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Bright auroral emissions during geomagnetic storms provide a good opportunity for testing the proposal that substorm onset is frequently triggered by plasma sheet flow bursts that are manifested in the ionosphere as auroral streamers. We have used the broad coverage of the ionospheric mapping of the plasma sheet offered by the highresolution THEMIS all-sky-imagers (ASIs) and chose the main phases of 9 coronal mass ejection (CME) related and 9 high-speed stream (HSS)-related geomagnetic storms, and identified substorm auroral onsets defined as brightening followed by poleward expansion. We found a detectable streamer heading to near the substorm onset location for all 60 onsets that we identified and were observed well by the ASIs. This indicates that substorm onsets are very often triggered by the intrusion of plasma with lower entropy than the surrounding plasma to the onset region, with the caveat that the ASIs do not give a direct measure of the intruding plasma. The majority of the triggering streamers are "tilted streamers, " which extend eastward as their eastern tip tilts equatorward to near the substorm onset location. Fourteen of the 60 cases were identified as "Harang streamers, " where the streamer discernibly turns toward the west poleward of reaching to near the onset latitude, indicating flow around the Harang reversal. Using the ASI observations, we observed substantially less substorm onsets for CME storms than for HSS storms, a result in disagreement with a recent finding of approximately equal substorm occurrences. We suggest that this difference is a result of strong non-substorm streamers that give substorm-like signatures in ground magnetic field observations but are not substorms based on their auroral signature. Our results from CME storms with steady, strong southward IMF are not consistent with the ~ 2-4 h repetition of substorms that has been suggested for moderate to strong southward IMF conditions. Instead, our results indicate substantially lower substorm occurrence during such steady driving conditions. Our results also show the much more frequent occurrence of substorms during HSS period, which is likely due to the highly fluctuating IMF.

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“…The similar statistical analysis can also be applied for substorms as well. It has been discussed for a long time that the amplitude of substorms basically follows lognormal distributions (e.g., Liou et al 2018). From the statistical analysis, Nakamura et al (2015) estimated the possible maximum amplitude of substorms as AE = ~ 4100 nT.…”

Section: Introductionmentioning

confidence: 99%

Extreme geomagnetic activities: a statistical study

Kataoka

2020

Earth Planets Space

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Statistical distributions are investigated for magnetic storms, sudden commencements (SCs), and substorms to identify the possible amplitude of the one in 100-year and 1000-year events from a limited data set of less than 100 years. The lists of magnetic storms and SCs are provided from Kakioka Magnetic Observatory, while the lists of substorms are obtained from SuperMAG. It is found that majorities of events essentially follow the log-normal distribution, as expected from the random output from a complex system. However, it is uncertain that large-amplitude events follow the same log-normal distributions, and rather follow the power-law distributions. Based on the statistical distributions, the probable amplitudes of the 100-year (1000-year) events can be estimated for magnetic storms, SCs, and substorms as approximately 750 nT (1100 nT), 230 nT (450 nT), and 5000 nT (6200 nT), respectively. The possible origin to cause the statistical distributions is also discussed, consulting the other space weather phenomena such as solar flares, coronal mass ejections, and solar energetic particles.

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Substorm Occurrence and Intensity Associated With Three Types of Solar Wind Structure

Cited by 20 publications

References 71 publications

Control of the East‐West Component of the Interplanetary Magnetic Field on the Occurrence of Magnetic Substorms

Control of the East‐West Component of the Interplanetary Magnetic Field on the Occurrence of Magnetic Substorms

Stormtime substorm onsets: occurrence and flow channel triggering

Extreme geomagnetic activities: a statistical study

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