Acceleration from Field-Aligned Potential Drops

Haerendel, G.

doi:10.1017/s0252921100078076

Cited by 17 publications

(41 citation statements)

References 27 publications

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“…Through resonant cyclotron interactions of the particles with the waves, electrons and protons will be pitch angle scattered into the loss cone (see Tsurutani and Lakhina, 1997) and lost into the upper atmosphere . Other mechanisms are the generation and damping of Alfvé n waves (Haerendel, 1994) and field-aligned current intensifications and dissipation (Araki, 1994). We refer the interested reader to recent experimental observations of a shock aurora by Motoba et al (2009).…”

Section: Ffss and Dayside Aurorasmentioning

confidence: 99%

A review of interplanetary discontinuities and their geomagnetic effects

Tsurutani

Lakhina

Verkhoglyadova

et al. 2011

Journal of Atmospheric and Solar-Terrestrial Physics

119

116

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Section: Ffss and Dayside Aurorasmentioning

confidence: 99%

A review of interplanetary discontinuities and their geomagnetic effects

Tsurutani

Lakhina

Verkhoglyadova

et al. 2011

Journal of Atmospheric and Solar-Terrestrial Physics

119

116

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“…The key parameters characterizing auroral arcs are based on two crucial assumptions. The first one is that the free energy content of a flux tube above an auroral arc is drained by the energy conversion process in the acceleration region, or “fracture zone”, within 4 Alfvén transit times, τ A , from equator to ionosphere [see also Haerendel , 1994]. The other one is that during that period practically all free energy (i.e., the fraction δ ), magnetic and internal, is converted into kinetic energy of the particle beams.…”

Section: Basic Relationsmentioning

confidence: 99%

“…The basic concept is that the band of enhanced conductivity acts as a transformer converting energy stored in the equatorward moving plasma and field into energy of an arc‐associated Boström Type II current system, inside which it is largely consumed by the auroral acceleration process and to a lesser extent fed into longitudinal shear stresses and associated internal energy of the source plasma. If this gain were sufficiently large, one should expect to see an effect on the arc's proper motion, which the author has interpreted as the manifestation of the release of shear stresses and magnetic energy from the region adjacent to the arc [see Haerendel , 1994; Haerendel et al , 1993; Frey et al , 1996]. However, this proper motion would be much slower than assumed in the model of Rothwell et al [1988].…”

Section: Introductionmentioning

confidence: 99%

Auroral arcs as current transformers

Haerendel

2008

J. Geophys. Res.

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[1] We treat the effects of an electric field tangential to an auroral arc on the basis of an analytical model according to which auroral arcs are energized by the release of magnetic shear stresses and associated internal energy (Haerendel, 2007). If the tangential field exceeds a certain (low) threshold, the ionosphere acts as a current generator, or better transformer, and the magnetosphere as the load. The reason is that energy supplied by a longitudinal Type I current system, as defined by Boström in 1964, is transformed into energy of the latitudinal Type II current system attached to the arc and is mostly consumed by the auroral acceleration process. Closure of the transformer current in the upper magnetosphere and energy deposition in form of internal energy and shear stresses, although small, are crucial for the operation of this process. It can be visualized as a dragging of magnetic field and plasma along the arc in the direction of higher magnetospheric pressure enforced by the electric polarization field. This energy deposition from below is superimposed on the release of free energy supplied by the magnetospheric generator. Formulation of this scenario leads to a set of algebraic equations, whose solution provides quantitative answers on the interdependence of current closure, energy deposition, and enhanced auroral energy flux in relation to the imposed tangential electric field. Contrary to earlier expectations, the polarization field appears not as a consequence of current blockage, but as manifestation of its continuation by field-aligned currents and their closure in the magnetosphere. Another consequence of the energy deposition from below is a small modification of the arc's proper motion in the ambient plasma frame. A procedure for evaluating applicable measurements in terms of the underlying physics is given and a concrete example added.

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“…Therefore magnetic shearing may occur between those distorted magnetic field lines and the field lines at lower L shells. Haerendel [1994] has shown that this magnetic shearing can generate field‐aligned currents due to the decoupling of the plasma, which allows fast stress relief. The generation of the unstable field‐aligned currents is a process that converts energy stored in magnetic shear stresses initiated from the shock compression into kinetic energy.…”

Section: Possible Mechanisms Of Particle Precipitation and Auroral Formsmentioning

confidence: 99%

Shock aurora: FAST and DMSP observations

et al. 2003

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[1] Global signatures of the aurora caused by interplanetary shocks/pressure pulses have been studied in recent years using ultraviolet imager data from polar orbiting spacecraft. The signatures include the occurrence of the aurora first near local noon and then propagation antisunward along the auroral oval at very high speeds. To better understand the mechanisms of particle precipitation, in this paper we study shock auroras using nearEarth observations of the FAST and DMSP satellites. We have studied the events that occurred during 1996-2000 where FAST and/or DMSP crossed the dawnside or duskside auroral zone within 10 min after shocks/pressure pulses arrived at the nose of the magnetopause. It is found that the electron precipitation increased significantly above the dawnside and duskside auroral oval zone after the shock/pressure pulse arrivals. The precipitation structure is low-energy electrons (<$1 keV) at higher latitudes ($75°-83°I LAT within 0600-0900 MLT) and high-energy electrons ($1-10 keV) at lower latitudes ($65°-79°ILAT) of the auroral zone. There are a few degrees (1°-4°ILAT) of overlap between these two categories of precipitated electrons. The precipitation of low-energy electrons was along highly structured field-aligned currents. The precipitation of the high-energy electrons was highly isotropic filling the loss cone. Possible mechanisms of field-aligned current generation are some dynamic processes occurring on the dayside magnetopause, such as magnetic shearing, magnetopause perturbation, magnetic reconnection, and Alfvén wave generation. Adiabatic compression might have caused the high-energy electron precipitation. On the basis of observations of FAST and DMSP, shock auroras are speculated to be diffuse auroras at the lower latitudes of the dayside auroral oval and discrete auroras on the poleward boundary of the oval with a few latitude degree overlap of the two types of auroras.

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Acceleration from Field-Aligned Potential Drops

Cited by 17 publications

References 27 publications

A review of interplanetary discontinuities and their geomagnetic effects

A review of interplanetary discontinuities and their geomagnetic effects

Auroral arcs as current transformers

Shock aurora: FAST and DMSP observations

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