Simulations of Alfvén waves in the geomagnetic tail and their auroral signatures

Wright, Andrew N.; Allan, W.

doi:10.1029/2007ja012464

Cited by 19 publications

(16 citation statements)

References 31 publications

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“…The eigenmode structure of MHD waves in the magnetotail geometry has been considered for many years (e.g., Patel, 1968;Siscoe, 1969;McKenzie, 1970;Hopcroft and Smith, 1985;Seboldt, 1990;Rickard and Wright, 1994;Wright, 1998, 2000;Wright and Allan, 2008;Lee and Hau, 2008). These studies show that the magnetotail can constitute a waveguide for compressional mode waves.…”

Section: Numerical Modelmentioning

confidence: 99%

“…A final mechanism that will be considered for field-aligned current generation is linear mode conversion at the plasma sheet boundary layer (e.g., Hasegawa, 1976;Goertz and Smith, 1989;Harrold et al, 1990;Wright, 1998, 2000;and Wright and Allan, 2008). If fast mode waves are produced in the plasma sheet, they will propagate nearly isotropically through the sheet, and will quickly reach the boundary layer.…”

Section: Introductionmentioning

confidence: 99%

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Propagation of Alfvén waves in the magnetotail during substorms

2009

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Abstract. Recent observations from the THEMIS mission have focused attention on the timing of events in the magnetotail during magnetospheric substorms and other periods of geomagnetic activity. Standard models of substorms have generally emphasized convective flows as the major source of energy and momentum transport; however, Alfvén wave propagation can also be an important transport mechanism. The propagation of Alfvén waves and the related field-aligned currents are studied by means of ideal MHD simulation of the tail. Perturbations of the cross-tail current can lead to the generation of such waves, and the resulting propagation both through the tail and along the plasma sheet boundary layer can lead to enhanced transport. Implications of this wave propagation on the interpretation of results from the THEMIS mission will be discussed.

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Section: Numerical Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Propagation of Alfvén waves in the magnetotail during substorms

2009

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“…Such mode conversion at the plasma sheet boundary layer has been considered by many authors [e.g., Hasegawa, 1976;Goertz and Smith, 1989;Harrold et al, 1990;Wright, 1998, 2000;Wright and Mann, 2006;Wright and Allan, 2008;Lysak et al, 2009]. Much of this work has considered waves propagating inward from the magnetopause to the boundary layer, while our emphasis here will be on fast mode waves in the plasma sheet propagating outward to the boundary layer.…”

Section: Introductionmentioning

confidence: 99%

“…Much of this work has considered waves propagating inward from the magnetopause to the boundary layer, while our emphasis here will be on fast mode waves in the plasma sheet propagating outward to the boundary layer. In particular, Wright and Allan [2008] have modeled this interaction using a two dimensional model in which the Alfvén speed is constant along the background magnetic field and which assumes a fixed k y dependence in the dawn-dusk direction. Thus, effects resulting from the inhomogeneity of the plasma along magnetic field lines as well as the true geometric mapping due to the convergence of magnetic field lines as they approach the ionosphere are not included in this model.…”

Section: Introductionmentioning

confidence: 99%

Development of parallel electric fields at the plasma sheet boundary layer

Lysak

Song

2011

J. Geophys. Res.

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[1] Many measurements of auroral particles, in particular recent measurements from the FAST satellite, indicate that the auroral electron distribution is often broad in energy and field-aligned in pitch angle. Such electrons are seen in conjunction with strong kinetic Alfvén waves with small perpendicular wavelength, and so the aurora produced by these electrons has been termed the "Alfvénic aurora." The Alfvénic aurora is predominant at the polar cap boundary of the aurora as well as in the auroral arc that brightens during substorm onset. The process of forming parallel electric fields in Alfvén waves has been investigated by means of three-dimensional two-fluid simulations. Waves with small perpendicular wavelengths can be produced by phase mixing when perpendicular gradients are present in the plasma. At lower altitudes, Alfvén waves can interact with the ionospheric Alfvén resonator and phase mix to scales of a few kilometers. At higher altitudes, the electron thermal speed becomes comparable or larger than the Alfvén speed, and parallel electric fields due to the Landau resonance can develop. This has been modeled in the fluid code by an approximation to the plasma dispersion function used in kinetic theory. Phase mixing is most effective when there are strong gradients, such as at the plasma sheet boundary layer. Simulations indicate that these processes can produce parallel electric fields on scales of a few kilometers (in the cold plasma case) to a few tens of kilometers (in the warm plasma case), comparable to the scale sizes of auroral arcs.

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“…The simulations of a cylindrical flux tube discussed in this paper can be regarded as complementing the simulations and modeling of a Cartesian (slab) flux tube performed by Wright et al (1999), Allan & Wright (1998, and Wright & Allan (2008). The context of these studies was the Earth's magnetotail, part of the Earth's magnetosphere which has a rich history of MHD wave coupling studies (see, e.g., the review by Wright & Mann 2006).…”

Section: Introductionmentioning

confidence: 99%

Coupled Alfvén and Kink Oscillations in Coronal Loops

Pascoe

Wright

Moortel

2010

ApJ

119

163

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Observations have revealed ubiquitous transverse velocity perturbation waves propagating in the solar corona. However, there is ongoing discussion regarding their interpretation as kink or Alfvén waves. To investigate the nature of transverse waves propagating in the solar corona and their potential for use as a coronal diagnostic in MHD seismology, we perform three-dimensional numerical simulations of footpoint-driven transverse waves propagating in a low β plasma. We consider the cases of both a uniform medium and one with loop-like density structure and perform a parametric study for our structuring parameters. When density structuring is present, resonant absorption in inhomogeneous layers leads to the coupling of the kink mode to the Alfvén mode. The decay of the propagating kink wave as energy is transferred to the local Alfvén mode is in good agreement with a modified interpretation of the analysis of Ruderman & Roberts for standing kink modes. Numerical simulations support the most general interpretation of the observed loop oscillations as a coupling of the kink and Alfvén modes. This coupling may account for the observed predominance of outward wave power in longer coronal loops since the observed damping length is comparable to our estimate based on an assumption of resonant absorption as the damping mechanism.

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Simulations of Alfvén waves in the geomagnetic tail and their auroral signatures

Cited by 19 publications

References 31 publications

Propagation of Alfvén waves in the magnetotail during substorms

Propagation of Alfvén waves in the magnetotail during substorms

Development of parallel electric fields at the plasma sheet boundary layer

Coupled Alfvén and Kink Oscillations in Coronal Loops

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