Sausage mode instability of thin current sheets as a cause of magnetospheric substorms

Büchner, Jörg; Kuska, Jens-Peer

doi:10.1007/s005850050788

Cited by 29 publications

(32 citation statements)

References 30 publications

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“…Recent three-dimensional simulations (Rogers et al, 2000;Hesse et al, 2001b;Zeiler et al, 2002) support the view that collisionless magnetic reconnection in 3-D current sheets operates in a manner very similar to the results derived from translationally invariant models. The development of structure in the out-of-plane direction appears to be limited to small scales which may enhance local dissipation coefficients (Huba et al, 1978;Büchner, 1998;Büchner and Kuska, 1999) but which do not alter the large-scale flow patterns.…”

Section: Magnetic Tearing or Reconnection Kinetic Modelsmentioning

confidence: 99%

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Dynamics of thin current sheets: Cluster observations

et al. 2007

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Abstract. The paper tries to sort out the specific signatures of the Near Earth Neutral Line (NENL) and the Current Disruption (CD) models, and looks for these signatures in Cluster data from two events. For both events transient magnetic signatures are observed, together with fast ion flows. In the simplest form of NENL scenario, with a large-scale two-dimensional reconnection site, quasi-invariance along Y is expected. Thus the magnetic signatures in the S/C frame are interpreted as relative motions, along the X or Z direction, of a quasi-steady X-line, with respect to the S/C. In the simplest form of CD scenario an azimuthal modulation is expected. Hence the signatures in the S/C frame are interpreted as signatures of azimuthally (along Y) moving current system associated with low frequency fluctuations of J y and the corresponding field-aligned currents (J x ). Event 1 covers a pseudo-breakup, developing only at high latitudes. First, a thin (H ≈2000 km≈2ρ i , with ρ i the ion gyroradius) Current Sheet (CS) is found to be quiet. A slightly thinner CS (H ≈1000-2000 km≈1-2ρ i ), crossed about 30 min later, is found to be active, with fast earthward ion flow bursts (300-600 km/s) and simultaneous large amplitude fluctuations (δB/B∼1). In the quiet CS the current density J y is carried by ions. Conversely, in the active CS ions are moving eastward; the westward current is carried by electrons that move eastward, faster than ions. Similarly, the velocity of earthward flows (300-600 km/s), observed during the active period, maximizes near or at the CS center. During the active phase of Event 1 no signature of the crossing of an X-line is identified, but an X-line located beyond Cluster could account for the observed ion flows, provided that it is active for at least 20 min. Ion flow bursts can also be Correspondence to: W. Baumjohann (baumjohann@oeaw.ac.at) due to CD and to the corresponding dipolarizations which are associated with changes in the current density. Yet their durations are shorter than the duration of the active period. While the overall ∂B z /∂t is too weak to accelerate ions up to the observed velocities, short duration ∂B z /∂t can produce the azimuthal electric field requested to account for the observed ion flow bursts. The corresponding large amplitude perturbations are shown to move eastward, which suggests that the reduction in the tail current could be achieved via a series of eastward traveling partial dipolarisations/CD. The second event is much more active than the first one. The observed flapping of the CS corresponds to an azimuthally propagating wave. A reversal in the proton flow velocity, from −1000 to +1000 km/s, is measured by CODIF. The overall flow reversal, the associated change in the sign of B z and the relationship between B x and B y suggest that the spacecraft are moving with respect to an X-line and its associated Hall-structure. Yet, a simple tailward retreat of a largescale X-line cannot account for all the observations, since several flow reversals are observed. These ...

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Section: Magnetic Tearing or Reconnection Kinetic Modelsmentioning

confidence: 99%

“…The magnetic field By is normalized by the initial lobe magnetic field B 0 , and the electric field is normalized by E 0 =B 0 V A /c. Note that the Earth is to the right in this figure. and Kuska, 1999) and in approximate linear theories (see e.g. Yoon and Lui, 2001, for a review).…”

Section: Cross-tail Modes and Current Disruptionmentioning

confidence: 99%

Dynamics of thin current sheets: Cluster observations

et al. 2007

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“…Theoretically, the possible wave modes in the magnetotail are investigated by solving the MHD equations using the Harris model as an equilibrium around which the various fields are perturbed. Examples of this method can be found in Roberts (1981a, b), Lee et al (1988), Smith et al (1997), Tirry et al Correspondence to: M. Volwerk (Martin.Volwerk@assoc.oeaw.ac.at) (1997), Büchner and Kuska (1999), Yoon and Lui (2001) and Fruit et al (2002a, b).…”

Section: Introductionmentioning

confidence: 99%

Compressional waves in the Earth's neutral sheet

et al. 2004

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Abstract. Compressional waves in the Earth's current sheet, driven by the high-speed plasma flows connected to substorms, are investigated using the Cluster magnetometer and plasma instrument. During the time that Cluster had its apogee in the magnetotail (July through October 2001), we have studied 5 events in detail. We find compressional waves in the 30-60 mHz band, at a spectral power density that is dependent on when and where the event is observed. There is a difference of two orders of magnitude in power density between waves at substorm onset and waves during quiet times. Strong plasma flows are the driver of the wave power. The spacecraft location in the current sheet is also important for the spectral power density. Having four spacecraft available we can discern spatial from temporal variations. We have determined the propagation direction of the waves in the 30-60 mHz band and found that in the Cluster rest frame they propagate in the same direction as the plasma flow at an angle 30 • < φ < 40 • with respect to the plasma flow direction in the spacecraft' rest frame.

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“…This is an appropriate way to investigate the pure effects of the magnetic guide field without perturbation occurring due to instabilities in the current direction (e.g. Büchner and Kuska, 1999). As a next logical step towards a full understanding of kinetic magnetic reconnection under the influence of a magnetic guide field, we plan to take these effects into consideration, leading to 3D simulations in the configuration space (6D in phase space).…”

Section: Discussionmentioning

confidence: 99%

Evolution of magnetic helicity under kinetic magnetic reconnection: Part II B ≠ 0 reconnection

Wiegelmann

Büchner

2002

Nonlin. Processes Geophys.

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Abstract.We investigate the evolution of magnetic helicity under kinetic magnetic reconnection in thin current sheets. We use Harris sheet equilibria and superimpose an external magnetic guide field. Consequently, the classical 2D magnetic neutral line becomes a field line here, causing a B = 0 reconnection. While without a guide field, the Hall effect leads to a quadrupolar structure in the perpendicular magnetic field and the helicity density, this effect vanishes in the B = 0 reconnection. The reason is that electrons are magnetized in the guide field and the Hall current does not occur. While a B = 0 reconnection leads just to a bending of the field lines in the reconnection area, thus conserving the helicity, the initial helicity is reduced for a B = 0 reconnection. The helicity reduction is, however, slower than the magnetic field dissipation. The simulations have been carried out by the numerical integration of the Vlasov-equation.

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Sausage mode instability of thin current sheets as a cause of magnetospheric substorms

Cited by 29 publications

References 30 publications

Dynamics of thin current sheets: Cluster observations

Dynamics of thin current sheets: Cluster observations

Compressional waves in the Earth's neutral sheet

Evolution of magnetic helicity under kinetic magnetic reconnection: Part II B ≠ 0 reconnection

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