Cavity resonators and Alfvén resonance cones observed on Freja

Stasiewicz, K.; Gustafsson, G.; Marklund, Göran; Lindqvist, Per‐Arne; Clemmons, J. H.; Zanetti, L. J.

doi:10.1029/96ja03462

Cited by 97 publications

(90 citation statements)

References 39 publications

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“…A more likely explanation is mode conversion to electron inertial Alfvén waves (represented as a schematic in Fig. 10), as the spatial scale of roughly 50 km is similar to 10 electron inertial lengths (λ e = m e µ 0 n e e 2 ), and is a feature seen in other studies, where an Alfvén wave is incident upon small-scale density cavities in the auroral acceleration region (Stasiewicz et al, 1997;Drozdenko and Morales, 2000). Interestingly, electron inertial effect also places this scale as a lower limit that can be achieved through phase mixing before radiation as inertial Alfvén waves prevent further phase mixing (Wei et al, 1994;Damiano et al, 2003).…”

Section: Figurementioning

confidence: 84%

An investigation of the field-aligned currents associated with a large-scale ULF wave using data from CUTLASS and FAST

et al. 2005

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Abstract. On 14 December 1999, a large-scale ULF wave event was observed by the Hankasalmi radar of the Super-DARN chain. Simultaneously, the FAST satellite passed through the Hankasalmi field-of-view, measuring the magnetic field oscillations of the wave at around 2000 km altitude, along with the precipitating ion and electron populations associated with these fields. A simple field line resonance model of the wave has been created and scaled using the wave's spatial and temporal characteristics inferred from SuperDARN and IMAGE magnetometer data. Here the model calculated field-aligned current is compared with field-aligned currents derived from the FAST energetic particle spectra and magnetic field measurements. This comparison reveals the small-scale structuring and energies of the current carriers in a large-scale Alfvén wave, a topic, which at present, is of considerable theoretical interest. When FAST traverses a region of the wave involving low upward field-aligned current densities, the current appears to be carried by unstructured downgoing electrons of energies less than 30 eV. A downward current region appears to be carried partially by upgoing electrons below the FAST energy detection threshold, but also consists of a mixture of hotter downgoing magnetospheric electrons and upgoing ionospheric electrons of energies <30 eV, with the hotter upgoing electrons presumably representing those upgoing electrons which have been accelerated by the wave field above the low energy detection threshold of FAST. A stronger interval of upward current shows that small-scale structuring of scale ∼50 km has been imposed on the current carriers, which are downgoing magnetospheric electrons of energy 0-500 eV.

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Section: Figurementioning

confidence: 84%

An investigation of the field-aligned currents associated with a large-scale ULF wave using data from CUTLASS and FAST

et al. 2005

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“…This property, first noticed by Mende et al [2003], but also noticeable in the data analyzed by Dubyagin et al [2003] has been confirmed by inspection of a number of FAST crossings over the THEMIS groundbased network by the author and H. Frey. The strong time dependence is revealed by the observation of magnetic and electric field oscillations at frequencies near 1 Hz [Stasiewicz et al, 1997].…”

Section: Current Systemsmentioning

confidence: 99%

“…Fortunately, there is plenty of evidence of smaller-scale components in the electric as well as magnetic fields [e.g., Stasiewicz et al, 1997;Chaston et al, 2002]. They are probably not impressed from the generator but may rather be a secondary product of the interaction of the incoming wider wave with the ionospheric resonator by multiple reflections with periods in the 1 Hz range [Stasiewicz et al, 1997;Chaston et al, 2002;Lysak and Song, 2002]. The associated low-altitude density cavities are instrumental in trapping the waves.…”

Section: Alfvénic Arcs/onset Arcsmentioning

confidence: 99%

Six auroral generators: A review

Haerendel

2011

J. Geophys. Res.

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[1] The paper reviews generator processes and configurations of six types of auroral arcs: embedded arcs, Alfvénic arcs, onset arcs, poleward arcs during substorms, auroral streamers, and auroral spirals. The arcs and generators are elements in global current systems, which are classified as Types I and II after Boström. The arcs may be dominated by transient processes or be quasi-stationary. The main emphasis of the paper is on the generator forces. They are pressure gradient forces, magnetic normal or shear stresses, or inertial forces. For three cases, the arcs embedded in the oval convection, the poleward arc during substorms, and the auroral streamers, simple expressions are presented of the currents injected into the ionosphere by the generator process, allowing quantitative evaluations. The relations leading from these currents to other key auroral quantities are summarized. The apparent conflict between the widths of Alfvénic arcs and the transverse scales required for energy coupling to the topside ionospheric plasma is solved by assuming current and field filamentation by multiple reflections in the ionospheric Alfvén resonator. The substorm generator is described as a high-beta plasma layer arising from collapse of the tail current sheet. An essential element in this process is the shedding of excess flux tube entropy through energy dumping in the auroral acceleration process and ionospheric dissipation. The dynamics of this process needs further investigation. The physics of the connection between flow bursts in the tail plasma sheet and the flows associated with auroral streamers in the ionosphere is discussed. Regular auroral spirals and the westward traveling surge have in common a concentration of upward field-aligned current which demands strongly enhanced dissipation. They differ by the processes creating the upward current concentration.

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“…The terminology used by these authors was unfortunate, because measurements made by Freja were done in a predominantly low beta environment, β<m e /m i , where kinetic Alfvén waves (KAW) do not exist. The observations were related to intense current structures j ∼100 µA m −2 on the electron inertial scale (Stasiewicz et al, 1997(Stasiewicz et al, , 1998Ivchenko and Marklund, 2002). The use of KAW terminology to describe electron inertial structures caused considerable confusion among other authors who continued to mix kinetic, finite-beta effects with electron inertial effects.…”

Section: Basic Observations and Measurementsmentioning

confidence: 99%

Dispersive MHD waves and alfvenons in charge non-neutral plasmas

Stasiewicz

Ekeberg

2008

Nonlin. Processes Geophys.

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Abstract. Dispersive properties of linear and nonlinear MHD waves, including shear, kinetic, electron inertial Alfvén, and slow and fast magnetosonic waves are analyzed using both analytical expansions and a novel technique of dispersion diagrams. The analysis is extended to explicitly include space charge effects in non-neutral plasmas. Nonlinear soliton solutions, here called alfvenons, are found to represent either convergent or divergent electric field structures with electric potentials and spatial dimensions similar to those observed by satellites in auroral regions. Similar solitary structures are postulated to be created in the solar corona, where fast alfvenons can provide acceleration of electrons to hundreds of keV during flares. Slow alfvenons driven by chromospheric convection produce positive potentials that can account for the acceleration of solar wind ions to 300-800 km/s. New results are discussed in the context of observations and other theoretical models for nonlinear Alfvén waves in space plasmas.

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Cavity resonators and Alfvén resonance cones observed on Freja

Cited by 97 publications

References 39 publications

An investigation of the field-aligned currents associated with a large-scale ULF wave using data from CUTLASS and FAST

An investigation of the field-aligned currents associated with a large-scale ULF wave using data from CUTLASS and FAST

Six auroral generators: A review

Dispersive MHD waves and alfvenons in charge non-neutral plasmas

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