Parallel electric fields

Knight, Stephen

doi:10.1016/0032-0633(73)90093-7

Cited by 740 publications

(785 citation statements)

References 11 publications

Supporting

Mentioning

755

Contrasting

Unclassified

Order By: Relevance

“…Most of the arcs are so-called inverted-V arcs which owe their energy and pitch angle distribution to the postacceleration of current carrying electrons precipitating out of the source region in the outer magnetosphere or nearEarth tail. The name "inverted-V" is derived from the typical appearance of the energy-time spectrograms due to the often nearly linear relation between accelerating potential and field-aligned current density [Knight, 1973;Lyons, 1980]. By contrast, Alfvénic arcs originate from Alfvén waves dumping a substantial fraction of their energy flux into "cold" electrons and ions in the topside ionosphere.…”

Section: Current Systemsmentioning

confidence: 99%

“…The pressure gradient force points out of the plane [Haerendel, 2007]. densities, whereby the famous Knight relation [Knight, 1973] is adopted for the conductance in the current voltage relation. This is interpreted as strong support for the concept that arcs embedded in the high-latitude convection system are nothing else than an enhanced mode of release of energy stored in the magnetic field by the magnetospheric pressure force interacting with the ionosphere.…”

Section: Embedded Arcsmentioning

confidence: 99%

“…e S C is the slightly modified Cowling conductivity and K the conductance in the current density-voltage relation of Knight [1973]. With these quantities defined, equation (7) can be solved for the electric field tangential to the poleward arc, E t , and all characteristic parameters of the arc and the ionospheric dissipation can be calculated as outlined in Appendix A.…”

Section: Poleward Arc Of the Auroral Bulgementioning

confidence: 99%

“…[49] The relation between the magnetic perturbation field, DB y,arc , of the auroral sheet current, J k,ion , and other key auroral parameters involves two further quantities, the transit time, t A , of an Alfvén wave between generator and ionosphere and the conductance parameter, K, of the Knight relation [Knight, 1973] between field-parallel potential drop and parallel current density, both of which can be readily derived from the adopted magnetosphere model. A third quantity, based on t A , is the impedance of the incoming Alfvén wave, R w .…”

Section: Appendix Amentioning

confidence: 99%

See 3 more Smart Citations

Six auroral generators: A review

Haerendel

2011

J. Geophys. Res.

View full text Add to dashboard Cite

[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.

show abstract

Section: Current Systemsmentioning

confidence: 99%

Section: Embedded Arcsmentioning

confidence: 99%

Section: Poleward Arc Of the Auroral Bulgementioning

confidence: 99%

Section: Appendix Amentioning

confidence: 99%

See 2 more Smart Citations

Six auroral generators: A review

Haerendel

2011

J. Geophys. Res.

View full text Add to dashboard Cite

show abstract

“…Two DAW active regions are situated at the edges of this region where the precipitating electrons probably give rise to the large integrated current by the constant flux of isotropic-with-a-losscone electrons. Since the associated field-aligned electric fields in this middle region are probably very small according to commonly used current-voltage relationships (e.g, Knight, 1973), this current, compared to that during strong Alfvén activity, is not easily cancelled out by the cold dense background plasma.…”

Section: Effect On Daw Induced Field-aligned Current Systemsmentioning

confidence: 99%

Electromagnetic waves and bursty electron acceleration: implications from Freja

et al. 2002

View full text Add to dashboard Cite

Abstract. Dispersive Alfvén wave activity is identified in four dayside auroral oval events measured by the Freja satellite. The events are characterized by ion injection, bursty electron precipitation below about 1 keV, transverse ion heating and broadband extremely low frequency (ELF) emissions below the lower hybrid cutoff frequency (a few kHz). Largescale density depletions/cavities, as determined by the Langmuir probe measurements, and strong electrostatic emissions are often observed simultaneously. A correlation study has been carried out between the E and B field fluctuations below 64 Hz and 10 Hz, respectively, (the DC instruments upper threshold) and the characteristics of the precipitating electrons. This study revealed that the energisation of electrons is indeed related to the broadband ELF emissions and that the electrostatic component plays a predominant role during very active magnetospheric conditions. Furthermore, the effect of the ELF electromagnetic emissions on the larger scale field-aligned current systems has been investigated, and it is found that such an effect cannot be detected. Instead, the Alfvénic activity creates a local region of field-aligned currents. It is suggested that dispersive Alfvén waves set up these local field-aligned current regions and, in turn, trigger more electrostatic emissions during certain conditions. In these regions, ions are transversely heated, and large-scale density depletions/cavities may be created during especially active periods.

show abstract

Solar cycle dependence of nightside field‐aligned currents: Effects of dayside ionospheric conductivity on the solar wind‐magnetosphere‐ionosphere coupling

et al. 2014

View full text Add to dashboard Cite

In the present study we observationally address the role of ionospheric conductivity in the solar wind‐magnetosphere coupling in terms of global field‐aligned currents (FACs). Solar EUV irradiance changes during a solar cycle and so does its contribution to the ionospheric conductivity. We statistically examine how, under fixed external conditions, the intensities of the R1 and R2 currents and their demarcation latitude depend on solar activity (F10.7). An emphasis is placed on nightside FACs in the dark hemisphere. The result shows that for fixed ranges of interplanetary electric field, the nightside FACs are more intense for higher solar activity irrespective of their polarities or local times. It is also found that the R1‐R2 pair, therefore the auroral oval, moves equatorward as the solar activity increases. For both current intensity and latitude, the dependence on F10.7 is more sensitive at smaller F10.7 and it levels off with increasing F10.7. The intensities of dayside FACs reveal similar F10.7 dependence as expected from the enhancement of the local ionospheric conductance. Interestingly, they also move equatorward with increasing F10.7. It is expected from force balance that as the dayside R1 current becomes more intense with increasing solar activity, the magnetosphere shrinks on the day side and expands on the night side. This configurational change of the magnetosphere presumably affects the energy transport from the solar wind to the magnetosphere, although its details still remain to be understood. We conclude that the ionospheric conductivity plays an active role in the solar wind‐magnetosphere‐ionosphere coupling.

show abstract

Parallel electric fields

Cited by 740 publications

References 11 publications

Six auroral generators: A review

Six auroral generators: A review

Electromagnetic waves and bursty electron acceleration: implications from Freja

Solar cycle dependence of nightside field‐aligned currents: Effects of dayside ionospheric conductivity on the solar wind‐magnetosphere‐ionosphere coupling

Contact Info

Product

Resources

About