Poleward-Moving Auroral Forms: What do We Really Know about them?

Fasel, G. J.; Minow, Joseph I.; Lee, L. C.; Smith, Roger W.; Deehr, C. S.

doi:10.1007/978-94-011-1052-5_15

Cited by 14 publications

(12 citation statements)

References 13 publications

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“…At the time of writing, only one set of measurements has compared magnetopause FTE observations with simultaneous observations of these poleward moving dayside cusp transients: Elphic et al [1990] presented observation of a few magnetopause FTEs that occurred at the time of a few poleward moving cusp/cleft auroral events and associated ionospheric flow channels. The distribution of repeat periods of poleward moving cusp auroral transients [Fasel et al, 1994] is very similar to that for magnetopause FTEs found by Lockwood and Wild [1993] and Kuo et al [1995], the mode value being about 3 rain and the average about 8 rain in both cases.…”

Section: Figure L a Shows The Original Fte Model Proposed Bysupporting

confidence: 81%

On the cause of a magnetospheric flux transfer event

Lockwood¹,

Hapgood²

1998

J. Geophys. Res.

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Abstract. We present a detailed investigation of a magnetospheric flux transfer event (FFE) seen by the Active Magnetospheric Tracer Explorer (AMPTE) UKS and IRM satellites around 1046 UT on October 28, 1984. This event has been discussed many times previously in the literature and has been cited as support for a variety of theories of FTE formation. We make use of a model developed to reproduce ion precipitations seen in the cusp ionosphere. The analysis confirms that the FTE is well explained as a brief excursion into an open low-latitude boundary layer (LLBL), as predicted by two theories of magnetospheric FTEs, namely, that they are bulges in the open LLBL due to reconnection rate enhancements or that they are indentations of the magnetopause by magnetosheath pressure increases (but in the presence of ongoing steady reconnection). The indentation of the inner edge of the open LLBL that these two models seek to explain is found to be shallow for this event. The ion model reproduces the continuous evolution of the ion distribution function between the sheath-like population at the event center and the surrounding magnetospheric populations; it also provides an explanation of the high-pressure core of the event as comprising field lines that were reconnected considerably earlier than those that are draped over it to give the event boundary layer. The magnetopause transition parameter is used to isolate a field rotation on the boundaries of the core, which is subjected to the tangential stress balance test. The test identifies this to be a convecting structure, which is neither a rotational discontinuity (Pal)) nor a contact discontinuity, but could possibly be a slow shock. In addition, evidence for ion reflection off a weak RD on the magnetospheric side of this structure is found. The event structure is consistent in many ways with features predicted for the open LLBL by analytic MHD theories and by MHD and hybrid simulations. The de HoffinanTeller velocity of the structure is significantly different from that of the magnetosheath flow, indicating that it is not an indentation caused by a high-pressure pulse in the sheath but is consistent with the motion of newly opened field lines (different from the sheath flow because of the magnetic tension force) deduced from the best fit to the ion data. However, we cannot here role out the possibility that the sheath flow pattern has changed in the long interval between the two satellites observing the FTE and subsequently emerging into the magnetosheath; thus this test is not conclusive in this particular case. Analysis of the fitted elapsed time since reconnection shows that the core of the event was reconnected in one pulse and the event boundary layer was reconnected in a subsequent pulse. Between these two pulses is a period of very low (but nonzero) reconnection rate, which lasts about 14 rains. Thus the analysis supports, but does not definitively verify, the concept that the FTE is a partial passage into an open LLBL caused by a traveling bulge in that layer pr...

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Section: Figure L a Shows The Original Fte Model Proposed Bysupporting

confidence: 81%

On the cause of a magnetospheric flux transfer event

Lockwood¹,

Hapgood²

1998

J. Geophys. Res.

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“…At the low-latitude magnetopause FTEs recur typically at 8-min intervals [Rijnbeek et al, 1984;Lockwood and Wild, 1993;Kuo et al, 1995]. This quasi-periodicity has been supported elsewhere by ionospheric observations of auroral transients [e.g., Fasel et al, 1994].…”

Section: Introductionsupporting

confidence: 62%

Cluster observations of quasi‐periodic impulsive signatures in the dayside northern lobe: High‐latitude flux transfer events?

et al. 2004

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[1] We report on a series of quasi-periodic reversals in GSM B Z observed by the four Cluster spacecraft in the northern dayside lobe poleward of the cusp on 23 February 2001. During an interval of about 35 min, multiple reversals (negative to positive) in B Z of approximately 1-min duration with an approximate 8-min recurrence time were observed. The individual structures do not resemble low-latitude flux transfer events (FTE) but the 8-min recurrence frequency suggests that intermittent reconnection may be occurring. Measurements (appropriately lagged) of the solar wind at ACE show that the IMF was southward-oriented with a strong B X and that a modest dynamic pressure increase occurred as the events started. The multi-point observations afforded by the Cluster spacecraft were used to infer the motion (direction and speed) of the observed magnetic field reversals. The associated currents were also calculated and they are consistent with the spatial confinement of the observed magnetic field reversals. We propose that the observed reversals are due to flux tubes reconnecting with closed field lines on the dayside. Ancillary data from the Cluster Ion Spectrometry (CIS) and Plasma Electron And Current Experiment (PEACE) instruments were used to develop a physical picture of the reversals.

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“…7b). These are present as quasi-periodic, intense auroral emissions and are poleward moving; namely, the poleward moving auroral forms (Fasel et al, 1994 between 0 and À5 nT, and B z shows a sharp increase from À6 to À1 nT, some transient brightening is present as rayed bundles within a weak, east-west rayed band between 1050 and 1140 UT (H 2 in Fig. 7b).…”

Section: Article In Pressmentioning

confidence: 95%

“…One peak, near noon, is dominated by a weak dayside corona with large diversity of structures, such as: rays, patches and drapery, and rapid changes in luminosity, displacement and appearance, while the other peak in the afternoon is mainly comprised of arc aurora. Furthermore, it has been documented that ground observations show a variety of auroral structures and activity in the 9-15 MLT sector, including the ''dayside breakup'' (Sandholt et al, 1990), ''poleward moving auroral forms (PMAFs)'' (Fasel et al, 1994) and multiple, discrete arcs (Moen et al, 1994). These transient dayside auroral phenomena have been interpreted as possible signatures of various plasma phenomena at the magnetopause and in the adjacent boundary layers, i.e.…”

Section: Introductionmentioning

confidence: 98%