Postmidnight convection dynamics during substorm expansion phase

Liang, J.; Sofko, G. J.; Frey, H. U.

doi:10.1029/2005ja011483

Cited by 12 publications

(25 citation statements)

References 37 publications

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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: 63%

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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Section: Discussionsupporting

confidence: 63%

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

et al. 2011

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“…Of course, the flow pattern is complicated further by smaller-scale perturbations which are imposed by localised changes in the conductivity, however, these are discussed in more detail below. The largerscale, azimuthally extended, Harang flows may actually correspond to the true form of the Kamide et al (1994) equatorward substorm convection cell as postulated by Liang et al (2006). In this case, however, these flows also appear to be intrinsically related to the enhanced auroral and sub-auroral flows described earlier.…”

Section: The Large-scale Picturementioning

confidence: 78%

“…7. Liang et al (2006) suggest that the MCS current system and associated eastward flows at auroral latitudes is a result of field line slippage (Lui and Kamide, 2003), whereas the SCW may be driven by reconnection. This is certainly consistent with the sub-auroral location of the MCS vs. the auroral location of the SCW.…”

Section: The Large-scale Picturementioning

confidence: 99%

“…They also found a systematic increase in the transpolar voltage from ∼40 kV 2 min before onset to ∼75 kV 12 min after, and attributed this to the removal of open flux from the polar cap by nightside reconnection. Recently, Liang et al (2006) (following earlier work by Kamide et al (1994)) discussed observations of two distinct systems in the substorm convection pattern. The first is a post-midnight anticlockwise convection vortex (PoACV) at higher latitudes and the second is an azimuthally extended clockwise vortex at lower latitudes.…”

Section: Introductionmentioning

confidence: 99%

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Towards a synthesis of substorm electrodynamics: HF radar and auroral observations

et al. 2006

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Abstract. At 08:35 UT on 21 November 2004, the onset of an interval of substorm activity was captured in the southern hemisphere by the Far UltraViolet (FUV) instrument on board the IMAGE spacecraft. This was accompanied by the onset of Pi2 activity and subsequent magnetic bays, evident in ground magnetic data from both hemispheres. Further intensifications were then observed in both the auroral and ground magnetic data over the following ∼3 h. During this interval the fields-of-view of the two southern hemisphere Tasman International Geospace Enviroment Radars (TIGER) moved through the evening sector towards midnight. Whilst initially low, the amount of backscatter from TIGER increased considerably during the early stages of the expansion phase such that by ∼09:20 UT an enhanced dusk flow cell was clearly evident. During the expansion phase the equatorward portion of this flow cell developed into a narrow high-speed flow channel, indicative of the auroral and subauroral flows identified in previous studies (e.g. Freeman et al., 1992;Parkinson et al., 2003). At the same time, higher latitude transient flow features were observed and as the interval progressed the flow reversal region and Harang discontinuity became very well defined. Overall, this study has enabled the spatial and temporal development of many different elements of the substorm process to be resolved and placed within a simple conceptual framework of magnetospheric convection. Specifically, the detailed observations of ionospheric flows have illustrated the complex interplay between substorm electric fields and associated auroral dynamics. They have helped define the distinct nature of different substorm current systems such as the traditional substorm current wedge and the more equatorward currents associated with polarisation electric fields. Additionally, they have Correspondence to: A. Grocott (a.grocott@ion.le.ac.uk) revealed a radar signature of nightside reconnection which provides the promise of quantifying nightside reconnection in a way which has already proved extremely successful in studies of the dayside magnetosphere.

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“…Recently, Liang et al (2006) (following earlier work by Kamide et al 1994) discussed observations of two distinct systems in the substorm convection pattern. The first is a postmidnight anticlockwise convection vortex (PoACV) at higher latitudes, and the second is an azimuthally extended clockwise vortex at lower latitudes.…”

Section: Substorm Expansion Phasementioning

confidence: 99%

A decade of the Super Dual Auroral Radar Network (SuperDARN): scientific achievements, new techniques and future directions

et al. 2007

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The Super Dual Auroral Radar Network (SuperDARN) has been operating as an international co-operative organization for over 10 years. The network has now grown so that the fields of view of its 18 radars cover the majority of the northern and southern hemisphere polar ionospheres. SuperDARN has been successful in addressing a wide range of scientific questions concerning processes in the magnetosphere, ionosphere,

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Postmidnight convection dynamics during substorm expansion phase

Cited by 12 publications

References 37 publications

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

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

Towards a synthesis of substorm electrodynamics: HF radar and auroral observations

A decade of the Super Dual Auroral Radar Network (SuperDARN): scientific achievements, new techniques and future directions

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