Formation of Auroral Arcs by Plasma Sheet Processes

2013 ◽  
pp. 266-269 ◽  
Author(s):  
W. J. Heikkila
Keyword(s):  
Plasma Sheet ◽  
Auroral Arcs

scholarly journals Ion shell distributions as free energy source for plasma waves on auroral field lines mapping to plasma sheet boundary layer

2004 ◽  
Vol 22 (6) ◽  
pp. 2115-2133 ◽  
Author(s):  
A. Olsson ◽  
P. Janhunen ◽  
W. K. Peterson
Keyword(s):  
Boundary Layer ◽  
Free Energy ◽  
Plasma Sheet ◽  
Wave Activity ◽  
Plasma Sheet Boundary Layer ◽  
In Situ Data ◽  
Bernstein Waves ◽  
Field Lines ◽  
Auroral Arcs ◽  
Polar Satellite

Abstract. Ion shell distributions are hollow spherical shells in velocity space that can be formed by many processes and occur in several regions of geospace. They are interesting because they have free energy that can, in principle, be transmitted to ions and electrons. Recently, a technique has been developed to estimate the original free energy available in shell distributions from in-situ data, where some of the energy has already been lost (or consumed). We report a systematic survey of three years of data from the Polar satellite. We present an estimate of the free energy available from ion shell distributions on auroral field lines sampled by the Polar satellite below 6 RE geocentric radius. At these altitudes the type of ion shells that we are especially interested in is most common on auroral field lines close to the polar cap (i.e. field lines mapping to the plasma sheet boundary layer, PSBL). Our analysis shows that ion shell distributions that have lost some of their free energy are commonly found not only in the PSBL, but also on auroral field lines mapping to the boundary plasma sheet (BPS), especially in the evening sector auroral field lines. We suggest that the PSBL ion shell distributions are formed during the so-called Velocity Dispersed Ion Signatures (VDIS) events. Furthermore, we find that the partly consumed shells often occur in association with enhanced wave activity and middle-energy electron anisotropies. The maximum downward ion energy flux associated with a shell distribution is often 10mWm-2 and sometimes exceeds 40mWm-2 when mapped to the ionosphere and thus may be enough to power many auroral processes. Earlier simulation studies have shown that ion shell distributions can excite ion Bernstein waves which, in turn, energise electrons in the parallel direction. It is possible that ion shell distributions are the link between the X-line and the auroral wave activity and electron acceleration in the energy transfer chain for stable auroral arcs.

Multiple auroral arcs and Birkeland currents: Evidence for plasma sheet boundary waves

1986 ◽  
Vol 13 (8) ◽  
pp. 805-808 ◽  
Author(s):  
P. F. Bythrow ◽  
M. A. Doyle ◽  
T. A. Potemra ◽  
L. J. Zanetti ◽  
R. E. Huffman ◽  
...  
Keyword(s):  
Plasma Sheet ◽  
Auroral Arcs ◽  
Birkeland Currents

Mapping of the statistical auroral distribution into the magnetosphere

1994 ◽  
Vol 72 (5-6) ◽  
pp. 266-269 ◽  
Author(s):  
Y. I. Feldstein ◽  
R. D. Elphinstone ◽  
D. J. Hearn ◽  
J. S. Murphree ◽  
L. L. Cogger
Keyword(s):  
Plasma Sheet ◽  
Large Scale ◽  
Source Region ◽  
Central Plasma ◽  
Discrete Structures ◽  
Central Plasma Sheet ◽  
Auroral Emissions ◽  
Auroral Arcs ◽  
Inner Region ◽  
Entry Layer

Statistical auroral distributions are used in combination with an empirical model of the Earth's magnetic field in an attempt to determine the large-scale magnetospheric source regions for various types of auroral luminosity. The narrow ring of structured auroral emissions during magnetically quiet intervals appears to be associated with the inner region of the nightside central plasma sheet and the dayside entry layer. Under active conditions these discrete structures expand to fill the entire central plasma sheet. The high-altitude boundary plasma sheet on the other hand is more likely to be related to diffuse auroral emissions poleward of this "oval" and to high-latitude polar auroral arcs. Under this scenario, the region of the magnetosphere bounded by the inner edge of the tail current sheet, the plasmasphere, and the dayside entry layer is the source region for the most equatorward diffuse auroral precipitation.

scholarly journals Possible role of magnetosphere-ionosphere coupling in auroral arc generation

2000 ◽  
Vol 18 (9) ◽  
pp. 1108-1117 ◽  
Author(s):  
W. Lyatsky ◽  
A. M. Hamza
Keyword(s):  
Growth Rate ◽  
Plasma Sheet ◽  
Alfven Waves ◽  
The Other ◽  
Alfven Wave ◽  
Alfvén Waves ◽  
Ionospheric Conductivity ◽  
Model Based ◽  
Field Aligned Current ◽  
Auroral Arcs

Abstract. Three models for the magnetosphere-ionosphere coupling feedback instability are considered. The first model is based on demagnetization of hot ions in the plasma sheet. The instability takes place in the global magnetosphere-ionosphere system when magnetospheric electrons drift through a spatial gradient of hot magnetospheric ion population. Such a situation exists on the inner and outer edges of the plasma sheet where relatively cold magnetospheric electrons move earthward through a radial gradient of hot ions. This leads to the formation of field-aligned currents. The effect of upward field-aligned current on particle precipitation and the magnitude of ionospheric conductivity leads to the instability of this earthward convection and to its division into convection streams oriented at some angle with respect to the initial convection direction. The growth rate of the instability is maximum for structures with sizes less than the ion Larmor radius in the equatorial plane. This may lead to formation of auroral arcs with widths about 10 km. This instability explains many features of such arcs, including their conjugacy in opposite hemispheres. However, it cannot explain the very high growth rates of some auroral arcs and very narrow arcs. For such arcs another type of instability must be considered. In the other two models the instability arises because of the generation of Alfven waves from growing arc-like structures in the ionospheric conductivity. One model is based on the modulation of precipitating electrons by field-aligned currents of the upward moving Alfven wave. The other model takes into consideration the reflection of Alfven waves from a maximum in the Alfven velocity at an altitude of about 3000 km. The growth of structures in both models takes place when the ionization function associated with upward field-aligned current is shifted from the edges of enhanced conductivity structures toward their centers. Such a shift arises because the structures move at a velocity different from the E×B drift. Although both models may work, the growth rate for the model, based on the modulation of the precipitating accelerated electrons, is significantly larger than that of the model based on the Alfven wave reflection. This mechanism is suitable for generation of auroral arcs with widths of about 1 km and less. The growth rate of the instability can be as large as 1 s-1, and this mechanism enables us to justify the development of auroral arcs only in one ionosphere. It is hardly suitable for excitation of wide and conjugate auroral arcs, but it may be responsible for the formation of small-scale structures inside a wide arc.Key words: Ionosphere (auroral ionosphere) - Magnetospheric physics (auroral phenomena; magnetosphere-ionosphere interactions)  

scholarly journals Ionospheric signatures of magnetospheric boundaries in the post-noon sector

2000 ◽  
Vol 18 (1) ◽  
pp. 74-80 ◽  
Author(s):  
S. T. Berry ◽  
L. Kersley ◽  
J. Moen ◽  
W. F. Denig
Keyword(s):  
Plasma Sheet ◽  
Auroral Ionosphere ◽  
Ionospheric Electron Density ◽  
Central Plasma ◽  
E Region ◽  
Boundary Plasma ◽  
Central Plasma Sheet ◽  
Auroral Arcs ◽  
Magnetospheric Boundaries ◽  
Latitudinal Band

Abstract. Spatial structures in ionospheric electron density revealed in a tomographic image have been identified with auroral forms and related to their sources in precipitating particles observed by DMSP satellites. The observations of plasma enhancements relate to discrete auroral arcs seen in the post-noon sector, identified by both red- and green-line emissions measured by a meridional scanning photometer. The features lie within a very narrow latitudinal band on L-shells where the satellite detectors observed electron precipitation classified as from the boundary plasma sheet (BPS). The harder particles are identified with an E-region structure, while further north the precipitation is softer, resulting in a localised F-layer blob and 630.0 nm emissions. A steep gradient in plasma density represent a signature in the ionosphere of the central plasma sheet (CPS)/BPS boundary. A transition to a less-structured F-layer is found on crossing the convection reversal boundary..Key words. Ionosphere (auroral ionosphere; ionosphere-magnetosphere interactions; polar ionosphere)

On The Relation Between Convection And Substorms

1996 ◽  
Author(s):  
Charles F. Kennel
Keyword(s):  
Time Resolution ◽  
Plasma Sheet ◽  
Substorm Onset ◽  
Auroral Ionosphere ◽  
Quantitative Understanding ◽  
Competing Models ◽  
Structured System ◽  
Auroral Arcs ◽  
Relationship Of ◽  
The Relationship

Why after 30 years of research have we not settled the relationship between substorms and convection? Why after 30 years are there still substantially different, competing models of substorm onset? Why has the progression from phenomenological to fully quantitative understanding not occurred? Answers to such questions will probably only become clear in retrospect, after the transition to quantitative understanding has taken place; in the meantime, we can only express our individual views. In our view, there have been three central difficulties. Contradictory pictures of plasma sheet transport have been able to flourish side-by-side because this fundamentally unsteady and highly spatially structured system was and is undersampled. As a result, people can still argue about when and where tail reconnection occurs in the substorm sequence, and other issues equally fundamental. Moreover, it is still not possible to connect the substorm onset in the auroral ionosphere to an event in space. For one thing, there is the timing problem: Waves communicate events’ existence across the magnetosphere and to the auroral ionosphere within a minute or two. We are only beginning to study the magnetoionosphere system globally with the required time resolution, and until we do so, there will be a “chicken and egg” problem. Finally, two key measurements are missing. No plasma sheet signatures of auroral arcs have been identified, so we do not know when a spacecraft is connected to a potential auroral onset region. We do not yet have an accepted ionospheric diagnostic of plasma sheet reconnection and the plasmoid formation; there is no auroral data display that illustrates at a glance the relationship of plasma sheet events to the onset and expansion of the substorm. Despite all this, there is real cause for optimism. The sheer magnitude of the observational effort and the volume and diversity of the results produced over the years have finally enabled us to perceive how complex the behavior of the magnetosphere really is. As our perceptions have evolved, we have designed multi-instrument, multi-spacecraft studies of ever-increasing comprehensiveness, articulation, and resolution, which further clarified our perceptions. All this effort is beginning to pay off.

scholarly journals Temporal and spatial evolution of discrete auroral arcs as seen by Cluster

2005 ◽  
Vol 23 (7) ◽  
pp. 2531-2557 ◽  
Author(s):  
S. Figueiredo ◽  
G. T. Marklund ◽  
T. Karlsson ◽  
T. Johansson ◽  
Y. Ebihara ◽  
...  
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Plasma Sheet ◽  
Large Scale ◽  
Potential Drop ◽  
Recovery Phase ◽  
Auroral Oval ◽  
Expansion Phase ◽  
Electric Fields And Currents ◽  
Auroral Arcs

Abstract. Two event studies are presented in this paper where intense convergent electric fields, with mapped intensities up to 1350 mV/m, are measured in the auroral upward current region by the Cluster spacecraft, at altitudes between 3 and 5 Earth radii. Both events are from May 2003, Southern Hemisphere, with equatorward crossings by the Cluster spacecraft of the pre-midnight auroral oval. Event 1 occurs during the end of the recovery phase of a strong substorm. A system of auroral arcs associated with convergent electric field structures, with a maximum perpendicular potential drop of about ~10 kV, and upflowing field-aligned currents with densities of 3 µA/m2 (mapped to the ionosphere), was detected at the boundary between the Plasma Sheet Boundary Layer (PSBL) and the Plasma Sheet (PS). The auroral arc structures evolve in shape and in magnitude on a timescale of tens of minutes, merging, broadening and intensifying, until finally fading away after about 50 min. Throughout this time, both the PS region and the auroral arc structure in its poleward part remain relatively fixed in space, reflecting the rather quiet auroral conditions during the end of the substorm. The auroral upward acceleration region is shown for this event to extend beyond 3.9 Earth radii altitude. Event 2 occurs during a more active period associated with the expansion phase of a moderate substorm. Images from the Defense Meteorological Satellite Program (DMSP) F13 spacecraft show that the Cluster spacecraft crossed the horn region of a surge-type aurora. Conjugated with the Cluster spacecraft crossing above the surge horn, the South Pole All Sky Imager recorded the motion and the temporal evolution of an east-west aligned auroral arc, 30 to 50 km wide. Intense electric field variations are measured by the Cluster spacecraft when crossing above the auroral arc structure, collocated with the density gradient at the PS poleward boundary, and coupled to intense upflowing field-aligned currents with mapped densities of up to 20 µA/m2. The surge horn consists of multiple arc structures which later merge into one structure and intensify at the PS poleward boundary. The surge horn and the associated PS region moved poleward with a velocity at the ionospheric level of 0.5 km/s, following the large-scale poleward expansion of the auroral oval associated with the substorm expansion phase. Keywords. Ionosphere (Ionosphere-magnetosphere interacctions; Electric fields and currents; Particle acceleration)

scholarly journals Latitude-energy structure of multiple ion beamlets in Polar/TIMAS data in plasma sheet boundary layer and boundary plasma sheet below 6 <i>R<sub>E</sub></i> radial distance: basic properties and statistical analysis

2005 ◽  
Vol 23 (3) ◽  
pp. 867-876 ◽  
Author(s):  
P. Janhunen ◽  
A. Olsson ◽  
W. K. Peterson ◽  
J. D. Menietti
Keyword(s):  
Boundary Layer ◽  
Plasma Sheet ◽  
Hollow Spheres ◽  
Radial Distance ◽  
Distribution Functions ◽  
Energy Structure ◽  
Plasma Sheet Boundary Layer ◽  
Basic Properties ◽  
Boundary Plasma ◽  
Auroral Arcs

Abstract. Velocity dispersed ion signatures (VDIS) occurring at the plasma sheet boundary layer (PSBL) are a well reported feature. Theory has, however, predicted the existence of multiple ion beamlets, similar to VDIS, in the boundary plasma sheet (BPS), i.e. at latitudes below the PSBL. In this study we show evidence for the multiple ion beamlets in Polar/TIMAS ion data and basic properties of the ion beamlets will be presented. Statistics of the occurrence frequency of ion multiple beamlets show that they are most common in the midnight MLT sector and for altitudes above 4 RE, while at low altitude (≤3 RE), single beamlets at PSBL (VDIS) are more common. Distribution functions of ion beamlets in velocity space have recently been shown to correspond to 3-dimensional hollow spheres, containing a large amount of free energy. We also study correlation with ~100 Hz waves and electron anisotropies and consider the possibility that ion beamlets correspond to stable auroral arcs.

Instability of the magnetosphere-ionosphere convection and formation of auroral arcs

1994 ◽  
Vol 12 (7) ◽  
pp. 636-641
Author(s):  
A. E. Kozlovsky ◽  
W. B. Lyatsky
Keyword(s):  
Steady State ◽  
Plasma Sheet ◽  
Electron Precipitation ◽  
Ionospheric Conductivity ◽  
Magnetospheric Convection ◽  
The Earth ◽  
Interchange Instability ◽  
Auroral Arcs

Abstract. In this paper we study an instability of the plasma moving towards the Earth near the inner plasma sheet boundary. We include both the interchange instability of the plasma sheet and the magnetosphere-ionosphere interaction instability caused by an effect of field-aligned currents (connected with electron precipitation) on ionospheric conductivity. The instability leads to the separation of steady-state magnetospheric convection into parallel layers. This instability may be responsible for the appearance of quiet auroral arcs inside region 2 of field-aligned currents flowing out of the ionosphere. This instability allows us to explain also the existence of crossing auroral arcs.

Sign in / Sign up

Export Citation Format

Share Document