Determination of the substorm initiation region from a major conjunction interval of THEMIS satellites

Lui, A. T. Y.; Angelopoulos, V.; Contel, O. Le; Frey, H. U.; Donovan, E.; Sibeck, D. G.; Liu, Wenlong; Auster, H. U.; Larson, D. E.; Li, X.; Nosé, M.; Fillingim, M. O.

doi:10.1029/2008ja013424

Cited by 47 publications

(68 citation statements)

References 82 publications

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“…These different dipolarization phenomena during substorm expansion phase imply that there is no one-to-one relationship between the near-Earth magnetic dipolarization and the high speed earthward ion bulk flow. This observation result is consistent with the result of Lui et al (2008). It suggests that the near-Earth dipolarization is a complex process, not a simple MHD process.…”

Section: Discussionsupporting

confidence: 82%

“…The mechanism of the magnetic field dipolarization is not resolved and it is still an open question. Some researchers (e.g., Birn and Hesse, 1996;Shiokawa et al, 1997;Birn et al, 1999;Nakamura et al, 2009) proposed that the dipolarization was correlative with the high-speed earthward bulk flows, but Lui et al (2008) pointed out that the dipolarization did not have a one-to-one relationship with the bursty bulk flow. The magnetic dipolarization onset at the midnight geosynchronous altitude was related to some plasma instabilities and prior to the auroral breakup.…”

Section: Introductionmentioning

confidence: 99%

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Multiple magnetic dipolarizations observed by THEMIS during a substorm

et al. 2011

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Abstract. The magnetic field dipolarization in the vicinity of substorm onset and during substorm expansion phase during the period of 06:00-06:40 UT on 15 February 2008 is investigated with observations from multiple probes of THEMIS. It is found that the magnetic dipolarization at the substorm onset (the onset time was about 06:14 UT) was not accompanied by obvious magnetic disturbance and ion bulk speed variation. The magnetic dipolarizations taking place during the substorm expansion phase observed by P4∼(−10.97, 2.04, −3.03) R E and P3∼(−11.32, 1.15, −3.10) R E were mostly accompanied by high speed earthward ion bulk flow, but the magnetic dipolarizations occurring during the substorm expansion phase observed by P5∼(−9.45, 1.07, −2.85) R E were not accompanied by high speed earthward ion bulk flow. Before substorm onset THEMIS P3, P4, P5 all observed the B x component fluctuation with a period of about 300 s. After substorm onset earthward high speed ion bulk flow and significant magnetic disturbances both occurred at P3 and P4 locations. These results indicate that there is no one-to-one relationship between the near-Earth magnetic dipolarization and the earthward ion bulk flow. In particular, the magnetic dipolarization occurring on the earthward side of the inner near-Earth plasma sheet is not accompanied by high speed earthward ion bulk flow. The dipolarization at substorm onset is a local and small scale phenomenon. There are multiple magnetic dipolarizations occurring during the substorm expansion phase. The dipolarization process is very complex and is not simply an MHD process. It is accompanied by some kinds of plasma instabilities, the plasma sheet azimuthal expansion not only by earthward ion bulk flow during substorm. A sharp increase of the AE index does not always give an accurate substorm onset time for substorm analysis.

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Section: Discussionsupporting

confidence: 82%

Section: Introductionmentioning

confidence: 99%

Multiple magnetic dipolarizations observed by THEMIS during a substorm

et al. 2011

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“…Otherwise the timing results could be flawed due to the delays caused by the aurora propagating azimuthally into the region of the THEMIS satellites. We note here that Lui et al (2008) discussed the timing of several events that occurred on 29 January 2008 with relatively little regards to their relative local time position to the THEMIS satellites. They based their analysis on preliminary optical data and they identified three onset events at ∼07:14, ∼07:42, 08:11 from the individual images in the 07:00 UT to 09:00 UT period.…”

Section: Discussion Of the 29 January 2008 Eventmentioning

confidence: 99%

Timing and location of substorm onsets from THEMIS satellite and ground based observations

et al. 2009

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Abstract. The unprecedented coverage of the THEMIS GBO station network coupled with high temporal and spatial resolution allowed us to determine the various stages of the global scale developments of the optical aurora at substorm onsets. We identified several steps of the substorm onset auroral phenomena and we suggest that the most rapid development is the starting of the Substorm Poleward Expansion (SPE) and it is most useful for accurate timing of the substorm onset. The physical significance of this step is the start of the large scale substorm energy dissipation in the atmosphere due to particle precipitation and auroral electrojet currents. We also recognized several pre-cursor features. We also measured the time of arrival of magnetic impulses associated with the same substorms at the THEMIS satellites. We used these times and a simple model with assumed iono-acoustic speeds in the range of 300-800 km/s to calculate the location and time of the origin of the magnetic impulses propagating from substorm onset. The assumption was made that the substorm occurred between two THEMIS satellites and the impulses propagated away from a singular starting point in and out along the magneto tail GSM-x axis. This technique is only useful in cases where the ground based signature of the substorm is very close in local time (or longitude) to the foot of the field lines of the THEMIS satellites. The x distance of the calculated origins were naturally highly dependent on the assumed propagation velocity model and the associated magneto-sonic speed. The resulting x distances of the starting point for the three events ranged between 11 and 17.6 R E . denoting a starting region that requires highly stretched field lines to map to the auroral onset latitude but which is generally considered to be too close forCorrespondence to: S. Mende (mende@ssl.berkeley.edu) neutral line formation. The corresponding start times were in the range of 0 to 170 s prior SPE depending strongly on the assumed propagation speed.

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“…Thus, most of the onsets shown above favor the near-earth initiation. A few supporting results for near-earth initiation of substorms have been published earlier based on data for individual substorm onset (e.g., Lui, 2008;Mende et al, 2009), which depend on a critical mapping of the configuration of the magnetic field in the magnetotail and its footprints in the ionosphere, or an accurate determination of the onset time of substorm expansion onset. However, this is not the case for this study.…”

Section: Discussionmentioning

confidence: 98%

“…In the CD model, on the other hand, substorm expansion onset must begin with the instabilities and cross-tail current sheet collapse at ∼ 8-10 R E , followed by the magnetic reconnection in the magnetotail. Both of the two models have found their supporting evidence by case studies (e.g., Angelopoulos et al, 2008;Lui, 2008), Published by Copernicus Publications on behalf of the European Geosciences Union. depending on the precise definition and the timing accuracy of the substorm signatures in various types of observations.…”

Section: Introductionmentioning

confidence: 95%

THEMIS and ground-based observations of successive substorm onsets following a super-long growth phase

et al. 2013

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We present four successive substorm events, which followed a super-long, as long as 9 h, growth phase on 5 December 2008, observed by the Time History of Events and Macroscale Interaction during Substorms (THEMIS) and the GOES 11 satellite with simultaneous coverage by the Alaska and THEMIS ground magnetometers. Several interesting and unique features were found for these cases. The interplanetary magnetic field was steadily southward and the solar wind speed was slow, less than 450 km s⁻¹, which are thought to drive the long growth phase for the following onsets. At least four substorm expansion onsets occurred, including a double-onset event, which appears to be a challenge to the reconnection hypothesis for double-onset substorm and favored an instability mechanism for the onsets and could not be explained by the two neutral line models. For the onsets at 09:32 UT and 09:42 UT, the dipolarization signature was observed by GOES 11, which was located earthward of THEMIS C and THEMIS B. THEMIS C satellite caught a delayed and much weaker signature 1–3 min after GOES 11. THEMIS B observed no relating signature. These observations provide us with direct evidence that these events initiated at the near-earth region. The observations of THEMIS C and THEMIS B around the onsets favor the near-earth instabilities model for substorm onset

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Determination of the substorm initiation region from a major conjunction interval of THEMIS satellites

Cited by 47 publications

References 82 publications

Multiple magnetic dipolarizations observed by THEMIS during a substorm

Multiple magnetic dipolarizations observed by THEMIS during a substorm

Timing and location of substorm onsets from THEMIS satellite and ground based observations

THEMIS and ground-based observations of successive substorm onsets following a super-long growth phase

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