Multiple overshoot and rebound of a bursty bulk flow

Panov, E. V.; Nakamura, R.; Baumjohann, W.; Angelopoulos, V.; Петрукович, А. А.; Retinò, Alessandro; Volwerk, M.; Takada, T.; Glaßmeier, K.‐H.; McFadden, J. P.; Larson, D. E.

doi:10.1029/2009gl041971

Cited by 162 publications

(207 citation statements)

References 24 publications

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“…It can be suggested that the observed fast azimuthal flows are similar to the flow patterns in the near-Earth plasma sheet that were recently observed using mainly the THEMIS spacecraft [Keika et al, 2009;Keiling et al, 2009;Ohtani et al, 2009;Panov et al, 2010aPanov et al, , 2010b. For example, Panov et al [2010b] showed by means of five THEMIS probes covering radial distances between 15 R E and 9 R E that the fast earthward flow in the magnetotail was largely deflected and reversed its direction tailward because of the increase in the radial pressure gradient.…”

Section: Discussionmentioning

confidence: 70%

Azimuthal auroral expansion associated with fast flows in the near-Earth plasma sheet: Coordinated observations of the THEMIS all-sky imagers and multiple spacecraft

et al. 2011

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[1] Fast azimuthal auroral expansion and poleward expansion are characteristic features of the expansion phase of substorms. In the first study of its kind, we have investigated the azimuthal auroral expansion and its magnetospheric counterpart using data from Time History of Events and Macroscale Interactions during Substorms (THEMIS) all-sky imagers and multiple spacecraft. During the tail season in 2008-2009, we found 16 events of azimuthally expanding aurora that passed near the magnetic footprints of the multiple spacecraft operating in the near-Earth plasma sheet. In the magnetosphere, these events commonly showed fast azimuthal and earthward flows associated with intense electric fields and magnetic dipolarization. The speed of the propagating structure, which was estimated from the time difference of the depolarization observed by the multiple spacecraft, was close to the measured azimuthal plasma flow velocity. We also found that this azimuthal plasma transport was dominated by the E × B drift speed associated with the enhanced electric field. In a statistical analysis, the averaged speeds of the leading edge of the westward and eastward auroral expansion were 8.8 and 5.3 km/s, respectively. When mapped onto the equatorial magnetosphere, these speeds (267 and 162 km/s) were comparable to the averaged azimuthal plasma (E × B) flow speeds observed by the spacecraft, which were 193 (239) km/s in the westward direction and 112 (139) km/s in the eastward direction. Our events showed that E × B flows and auroral expansion predominantly propagated westward, indicating an effect of westward background convection in the Harang flow shear. From these results, we concluded that the azimuthal auroral expansion was closely related to magnetic dipolarization which expanded azimuthally at the E × B drift speed. On the basis of the abrupt formation of the fast E × B flows and their propagation away from the onset location, we suggest that the effects of the intense large-scale electric fields, which are possibly generated through substorm onset turbulence, propagate to the ionosphere along the magnetic field lines and lead to azimuthal expansion of an auroral arc.

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Section: Discussionmentioning

confidence: 70%

Azimuthal auroral expansion associated with fast flows in the near-Earth plasma sheet: Coordinated observations of the THEMIS all-sky imagers and multiple spacecraft

et al. 2011

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“…Using MHD simulations, Wolf et al [2012] showed that neglect of inertial effects in bubble-injection situations where they are not negligible does not prevent RCM-E from correctly predicting total magnetic-flux transport, magnetic dipolarization, and the associated particle energization, because bubbles would eventually stop at their equilibrium locations in their simulations. However, both Panov et al [2010] and Wolf et al [2012] showed that bubbles may overshoot and rebound around their equilibrium location. Therefore, we speculate that bubbles could penetrate deeper into the inner magnetosphere when effects of their overshoot were taken into account than not, which implies that the contribution of bubbles to the ring current energy may increase further.…”

Section: Discussionmentioning

confidence: 99%

“…The increase of the induction electric field is associated with the magnetic field dipolarization, which is calculated self-consistently in the RCM-E. The increase of the potential electric field is associated with the buildup of charges on the edges of the bubble [e.g., Pontius and Wolf, 1990;Nakamura et al, 2001]. Therefore, we place a concentrated electric field along the sector of the boundary where the bubble is injected.…”

Section: 1002/2015ja021398mentioning

confidence: 99%

“…There are several arguments based on observations and theory suggesting that bursty bulk flows (BBFs) play an important role in the storm time ring current enhancement. BBFs are also commonly termed "bubbles," which are defined as bundles of flux tubes containing a lower value of the entropy parameter PV 5/3 than their neighbors [Pontius and Wolf, 1990], where P is the plasma pressure and V = ∫ds/B is the flux tube volume per unit magnetic flux. Bubbles accelerate to a high speed due to the earthward tension force inside their depleted flux tubes.…”

Section: Introductionmentioning

confidence: 99%

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On the contribution of plasma sheet bubbles to the storm time ring current

et al. 2015

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Particle injections occur frequently inside 10 Re during geomagnetic storms. They are commonly associated with bursty bulk flows or plasma sheet bubbles transported from the tail to the inner magnetosphere. Although observations and theoretical arguments have suggested that they may have an important role in storm time dynamics, this assertion has not been addressed quantitatively. In this paper, we investigate which process is dominant for the storm time ring current buildup: large‐scale enhanced convection or localized bubble injections. We use the Rice Convection Model‐Equilibrium (RCM‐E) to model a series of idealized storm main phases. The boundary conditions at 14–15 Re on the nightside are adjusted to randomly inject bubbles to a degree roughly consistent with observed statistical properties. A test particle tracing technique is then used to identify the source of the ring current plasma. We find that the contribution of plasma sheet bubbles to the ring current energy increases from ~20% for weak storms to ~50% for moderate storms and levels off at ~61% for intense storms, while the contribution of trapped particles decreases from ~60% for weak storms to ~30% for moderate and ~21% for intense storms. The contribution of nonbubble plasma sheet flux tubes remains ~20% on average regardless of the storm intensity. Consistent with previous RCM and RCM‐E simulations, our results show that the mechanisms for plasma sheet bubbles enhancing the ring current energy are (1) the deep penetration of bubbles and (2) the bulk plasma pushed ahead of bubbles. Both the bubbles and the plasma pushed ahead typically contain larger distribution functions than those in the inner magnetosphere at quiet times. An integrated effect of those individual bubble injections is the gradual enhancement of the storm time ring current. We also make two predictions testable against observations. First, fluctuations over a time scale of 5–20 min in the plasma distributions and electric field can be seen in the central ring current region for the storm main phase. We find that the plasma pressure and the electric field EY there vary over about 10%–30% and 50%–300% of the background values, respectively. Second, the maximum plasma pressure and magnetic field depression in the central ring current region during the main phase are well correlated with the Dst index.

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“…As shown by Birn et al [2004], flow vortices appear at the flanks of the bubble, twisting the magnetic field, and causing a downward (upward) field-aligned current at the dawnside (duskside) flank, and forming a local wedge like current system [e.g., Wolf, 1993, 1999;Sergeev et al, 1996a;Birn and Hesse, 1996;Birn et al, 1999Birn et al, , 2004Snekvik et al, 2007;Zhang et al, 2009]. A return plasma flow may occur at the flanks of the bubble, and the corresponding shear against the plasma flow in the bubble main channel may also be involved in the generation of the field-aligned currents [e.g., Chen and Wolf, 1999;Kauristie et al, 2000;Birn et al, 2004;Keiling et al, 2009;Ohtani et al, 2009;Walsh et al, 2009;Panov et al, 2010aPanov et al, , 2010bBirn et al, 2011;Ge et al, 2011;Pitkänen et al, 2011].…”

Section: Introductionmentioning

confidence: 99%

Energy conversion regions as observed by Cluster in the plasma sheet

et al. 2011

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[1] In this article we present a review of recent studies of observations of localized energy conversion regions (ECRs) observed by Cluster in the plasma sheet at altitudes of 15-20R E . By examining variations in the power density, E · J, where E is the electric field and J is the current density, we show that the plasma sheet exhibits a high level of fine structure. Approximately three times as many concentrated load regions (CLRs) (E · J > 0) as concentrated generator regions (CGRs) (E · J < 0) are identified, confirming the average load character of the plasma sheet. Some ECRs are found to relate to auroral activity. While ECRs are relevant for the energy conversion between the electromagnetic field and the particles, bursty bulk flows (BBFs) play a central role for the energy transfer in the plasma sheet. We show that ECRs and BBFs are likely to be related, although details of this relationship are yet to be explored. The plasma sheet energy conversion increases rather simultaneously with increasing geomagnetic activity in both CLRs and CGRs. Consistent with large-scale magnetotail simulations, most of the observed ECRs appear to be rather stationary in space but varying in time. We estimate that the ECR lifetime and scale size are a few minutes and a few R E , respectively. It is conceivable that ECRs rise and vanish locally in significant regions of the plasma sheet, possibly oscillating between load and generator character, while some energy is transmitted as Poynting flux to the ionosphere.

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Multiple overshoot and rebound of a bursty bulk flow

Cited by 162 publications

References 24 publications

Azimuthal auroral expansion associated with fast flows in the near-Earth plasma sheet: Coordinated observations of the THEMIS all-sky imagers and multiple spacecraft

Azimuthal auroral expansion associated with fast flows in the near-Earth plasma sheet: Coordinated observations of the THEMIS all-sky imagers and multiple spacecraft

On the contribution of plasma sheet bubbles to the storm time ring current

Energy conversion regions as observed by Cluster in the plasma sheet

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