Response of large‐scale ionospheric convection to substorm expansion onsets: A case study

Miyashita, Yukinaga; Hosokawa, K.; Hori, Tomoaki; Kamide, Y.; Yukimatu, A. S.; Fujimoto, M.; Mukai, T.; Machida, S.; Sato, Natsuo; Saito, Y.; Shinohara, I.; Sigwarth, J. B.

doi:10.1029/2008ja013586

Cited by 17 publications

(22 citation statements)

References 62 publications

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“…The magnitude and delay in the following velocity increase, however, were larger and shorter, respectively, than those reported previously [see Bristow and Jensen , 2007, Figure 8a], and perhaps more consistent with the trends reported by the latter group of studies. In particular, the enhanced eastward flows in the dawn convection cell associated with the second substorm reported here are reminiscent of those presented by Miyashita et al [2008].…”

Section: Discussionsupporting

confidence: 78%

“…One should note that despite recent advances the issue of auroral convection response to substorm onset is far from being resolved. Thus some studies showed a decrease in the ionospheric convection strength near the substorm onset time while others showed an increase (see recent study by Miyashita et al [2008, and references therein]). Our observations did show some decrease near the second substorm onset and thus appear to be consistent with the former group.…”

Section: Discussionmentioning

confidence: 99%

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Time evolution of the subauroral electric fields: A case study during a sequence of two substorms

et al. 2009

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[1] The temporal evolution of the subauroral polarization stream (SAPS) is investigated using the Doppler velocity observations by the Unwin HF radar in conjunction with the simultaneously observed auroral luminosity and plasma convection reversal regions. The event under study of 14 December 2004, 1000-1600 UT, occurred during geomagnetically quiet conditions when a sequence of two substorms separated by $2 hours was observed by the IMAGE satellite. It is shown that the SAPS appeared shortly after the first substorm onset and continued to dominate the westward plasma convection at subauroral magnetic latitudes 59°-63°S for $6 hours. An unexpected exception occurred near the second substorm onset time when a narrow channel of weaker SAPS westward convection became embedded in the slow eastward drifting plasma for a short $25-min period, which was attributed to the equatorward expansion of the dawn convection cell during the growth and expansion phases of the second substorm. Another remarkable plasma convection feature was observed in the same 25-min period $5°poleward of SAPS; this was a narrow ''mirror'' channel of the eastward drifting plasma parallel to the main SAPS channel. It is argued that the latter feature may also be caused by the equatorward expanding dawn convection cell whose streamlines become compressed by and aligned with the SAPS poleward edge. A possible relationship between the SAPS intensity and its position relative to the auroral oval is also investigated. The results suggest that the magnetosphere-ionosphere feedback processes within SAPS become more effective as the equatorward edge of the eastward convection region retreats poleward with the SAPS position much less affected by the auroral dynamics.

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Section: Discussionsupporting

confidence: 78%

Section: Discussionmentioning

confidence: 99%

Time evolution of the subauroral electric fields: A case study during a sequence of two substorms

et al. 2009

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“…The directly driven process has been found to be effective continuously throughout the entire lifetime of a substorm, and the unloading process works in the expansion phase [Kamide and Kokubun, 1996]. The increase in the potential drop in the growth phase is mainly due to the enhancement of the directly driven process, whereas the increase in the potential drop at the expansion phase is consistent with Liang et al [2004Liang et al [ , 2006, Provan et al [2004], and Miyashita et al [2008] in that the ionospheric electric field is enhanced, not reduced, in association with substorm expansion onset.…”

Section: Discussionsupporting

confidence: 64%

Spontaneous and trigger-associated substorms compared: Electrodynamic parameters in the polar ionosphere

et al. 2011

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[1] An attempt is made to study the difference, if any, between the response of the polar ionosphere to spontaneous substorms and that to trigger-associated substorms in terms of electrodynamic parameters including ionospheric current vectors, the electric potential, and the current function. The results show that, in the first approximation, the ionospheric parameters for the two types of substorms are quite similar. It is therefore conceived that spontaneous substorms are not very different from trigger-associated substorms in the development of substorm processes in the magnetosphere-ionosphere system. We demonstrate, however, that spontaneous substorms seem to have a more clearly identifiable growth phase, whereas trigger-associated substorms have a more powerful unloading process. Changes in the current intensity and the electric potential drop across the polar cap in the recovery phase are also quite different from each other. Both the current intensity and the cross-polar cap potential drop show a larger decrease in the recovery phase of trigger-associated substorms, but the potential drop decreases only slightly and the currents in the late morning sector are still strong for spontaneous substorms. We interpret these findings as an indication of the relative importance of the unloading process and the directly driven process in conjunction with the north-south polarity of the interplanetary magnetic field. There still exists a strong directly driven process in the recovery phase of spontaneous substorms. For trigger-associated substorms, however, both the directly driven process and the unloading process become weak after the peak time.

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“…However, variations of ionospheric electric fields associated with substorms are not well understood. For the high‐latitude ionosphere, Lyons et al [2003], Jayachandran et al [2003], and Bristow and Jensen [2007] reported that an abrupt and significant decrease of the ionospheric convection occurred at or just prior to the substorm onset, but Kamide et al [1996], Saka et al [2001], and Miyashita et al [2008]found that the ionospheric convection was enhanced at the onset. For the low‐latitude ionosphere, Sibeck et al [1998], Kikuchi et al [2000, 2003], Sastri et al [2001, 2003], and Wei et al [2009] reported that the dayside ionospheric electric field disturbance at substorm onset was westward and that the dayside geomagnetic field disturbance was a negative bay after the onset.…”

Section: Introductionmentioning

confidence: 99%

Statistical analysis of dayside equatorial ionospheric electric fields and electrojet currents produced by magnetospheric substorms during sawtooth events

Huang¹

2012

J. Geophys. Res.

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.[1] Substorms cause significant disturbances in the ionosphere. However, it has not been well understood how the electric field and electrojet in the dayside equatorial ionosphere respond to substorm onset. Previous studies found that the equatorial electric field, after substorm onset, could be eastward or westward. Because the onset of isolated substorms is often related to a northward turning of the interplanetary magnetic field (IMF), the measured total electric field is determined by contributions from both IMF northward turning and substorm onset and is not necessarily the signature of the onset. In order to exclude the effect of IMF northward turning, we analyze the variations of ionospheric electric field and electrojet during storm time substorms when the IMF remains stable. Thus, the ionospheric variations can be identified to be caused solely by substorms. The electric field data are measured by the Jicamarca radar, and the electrojet is derived from magnetometers at Jicamarca and Piura. It is found that substorm onset induces an eastward electric field and electrojet in the dayside equatorial ionosphere when the IMF remains continuously southward across the onset. The equatorial electrojet starts to increase at the onset, reaches a maximum value $30 min after the onset, and then decreases to the pre-onset value $60 min after the onset. Westward electric field and counter-electrojet occur only if the substorm onset is associated with a northward turning of the IMF. It is concluded that the effect of substorm onset on the dayside equatorial ionosphere, without involvement of IMF reorientations, is an enhanced eastward electric field.Citation: Huang, C.-S. (2012), Statistical analysis of dayside equatorial ionospheric electric fields and electrojet currents produced by magnetospheric substorms during sawtooth events,

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Response of large‐scale ionospheric convection to substorm expansion onsets: A case study

Cited by 17 publications

References 62 publications

Time evolution of the subauroral electric fields: A case study during a sequence of two substorms

Time evolution of the subauroral electric fields: A case study during a sequence of two substorms

Spontaneous and trigger-associated substorms compared: Electrodynamic parameters in the polar ionosphere

Statistical analysis of dayside equatorial ionospheric electric fields and electrojet currents produced by magnetospheric substorms during sawtooth events

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