Multi-instrument observations of ULF wave-driven discrete auroral arcs propagating sunward and equatorward from the poleward boundary of the duskside auroral oval

2004 ◽  
Vol 11 (4) ◽  
pp. 1250-1259 ◽  
Author(s):  
J. T. Mathews ◽  
I. R. Mann ◽  
I. J. Rae ◽  
J. Moen
Keyword(s):  
Auroral Oval ◽  
Ulf Wave ◽  
Auroral Arcs

scholarly journals Equatorward propagating auroral arcs driven by ULF wave activity: Multipoint ground- and space-based observations in the dusk sector auroral oval

2017 ◽  
Vol 122 (5) ◽  
pp. 5591-5605 ◽  
Author(s):  
L. J. Baddeley ◽  
D. A. Lorentzen ◽  
N. Partamies ◽  
M. Denig ◽  
V. A. Pilipenko ◽  
...  
Keyword(s):  
Auroral Oval ◽  
Wave Activity ◽  
Ulf Wave ◽  
Auroral Arcs ◽  
Dusk Sector

scholarly journals Correspondence between the latitudinal ULF wave power distribution and auroral oval in conjugate ionospheres

2018 ◽  
Author(s):  
V.A. Martines-Bedenko ◽  
V.A. Pilipenko ◽  
M.D. Hartinger ◽  
M.J. Engebretson ◽  
D.A. Lorentzen ◽  
...  
Keyword(s):  
Power Distribution ◽  
Auroral Oval ◽  
Wave Power ◽  
Ulf Wave

Discrete polar cap aurora observed from Spitsbergen

Polar Record ◽  
1992 ◽  
Vol 28 (166) ◽  
pp. 191-204 ◽  
Author(s):  
D.A.R. Simmons ◽  
K. Henriksen
Keyword(s):  
Auroral Oval ◽  
Plasma Convection ◽  
Electron Current ◽  
Polar Cap ◽  
Late Afternoon ◽  
Early Afternoon ◽  
Visual Characteristics ◽  
Auroral Arcs ◽  
Very High ◽  
Diurnal Rotation

ABSTRACTDiscrete auroral arcs frequently bridge the polar cap connecting the morning and evening sectors of the auroral oval along the line of the transpolar (electron) current. Very high-latitude stations that lie wholly within the oval during the earth's diurnal rotation pass under this bridge twice a day, giving morning and evening maxima. Stations at slightly lower latitudes on Spitsbergen lie within the oval in the evening but under, or even south of, the oval in the morning. From such stations the evening, but not the morning, maximum is readily observed. This study is primarily concerned with the orientation of discrete polar cap arcs in the evening skies over Spitsbergen. It shows that the geomagnetic alignment of these arcs is latitude-dependent between geomagnetic colatitudes 6 to 20°N. At the highest latitudes within this range, the arcs are in transpolar alignment, whereas at the lowest latitudes within the polar cap, they are oval-aligned. At intermediate latitudes, the arcs are observed in transitional phases between transpolar and ovalalignment. The solar alignment of discrete polar cap arcs is a function of corrected geomagnetic local time. In the early afternoon, solar alignment is poor but this gradually improves throughout the late afternoon until there is excellent alignment at the time of the evening maximum. Recent satellite studies of plasma convection in the polar ionosphere have helped to explain some of the visual characteristics of discrete polar cap aurora observed from Spitsbergen, particularly the irregular alignment of arcs in the region of the Harang discontinuity.

On the occurrence and characteristics of intense low-altitude electric fields observed by Freja

1995 ◽  
Vol 13 (7) ◽  
pp. 704-712 ◽  
Author(s):  
G. Marklund ◽  
L. Blomberg ◽  
C.-G. Fälthammar ◽  
P.-A. Lindqvist ◽  
L. Eliasson
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Early Morning ◽  
Auroral Oval ◽  
Small Scale ◽  
Auroral Region ◽  
Ion Heating ◽  
Intense Fields ◽  
Auroral Emissions ◽  
Auroral Arcs

Abstract. High-resolution measurements by the double probe electric field instrument on the Freja satellite are presented. The observations show that extremely intense (up to 1 V m–1) and fine-structured (<1 km) electric fields exist at auroral latitudes within the altitude regime explored by Freja (up to 1700 km). The intense field events typically occur within the early morning sector of the auroral oval (01–07 MLT) during times of geomagnetic activity. In contrast to the observations within the auroral acceleration region characterized by intense converging electric fields associated with electron precipitation, upward ion beams and upward field-aligned currents, the intense electric fields observed by Freja are often found to be diverging and located within regions of downward field-aligned currents outside the electron aurora. Moreover, the intense fields are observed in conjunction with precipitating and transversely energized ions of energies 0.5–1 keV and may play an important role in the ion heating. The observations suggest that the intense electric field events are associated with small-scale low-conductivity ionospheric regions void of auroral emissions such as east-west aligned dark filaments or vortex streets of black auroral curls located between or adjacent to auroral arcs within the morningside diffuse auroral region. We suggest that these intense fields also exist at ionospheric altitudes although no such observations have yet been made. This is possible since the height-integrated conductivity associated with the dark filaments may be as low as 0.1 S or less. In addition, Freja electric field data collected outside the auroral region are discussed with particular emphasis on subauroral electric fields which are observed within the 19–01 MLT sector between the equatorward edge of the auroral oval and the inner edge of the ring current.

scholarly journals Correspondence between the ULF wave power spatial distribution and auroral oval boundaries

2016 ◽  
Vol 2 (2) ◽  
pp. 35-45 ◽  
Author(s):  
Ольга Козырева ◽  
Olga Kozyreva ◽  
Вячеслав Пилипенко ◽  
Vyacheslav Pilipenko ◽  
Марк Энгебретсон ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Spectral Power ◽  
Recovery Phase ◽  
Temporal Variations ◽  
Auroral Oval ◽  
Wave Power ◽  
Observational Result ◽  
Ulf Wave ◽  
Image Satellite ◽  
Magnetospheric Field

The location of the auroral oval boundaries has been mapped onto the Pc5 wave power spatial distribution. The poleward and equatorward boundaries of auroral oval are estimated using either the BAS database based on UV observations of the aurora by the IMAGE satellite or the OVATION model based on the DMSP particle data. The epicenter of the spectral power of broadband fluctuations in the Pc5 band during storm growth phase is mapped inside the auroral oval. During the storm recovery phase, the spectral power of narrowband Pc5 waves, both in the morning and dusk sector, is mapped inside the auroral oval or around its equatorward boundary. This observational result confirms the effects earlier reported: the spatial/temporal variations of the Pc5 wave power in the morning/pre-noon sector are closely related to the location of the auroral electrojet and magnetospheric field-aligned currents. At the same time, narrowband Pc5 waves demonstrate typical resonant features in the amplitude-phase latitudinal structure. Thus, the location of the auroral oval (or its equatorward border) is the preferred latitude of magnetospheric field-line Alfven resonator excitation. This effect is not taken into account by modern theories of ULF Pc5 waves, but it could be significant for development of more adequate models.

scholarly journals Magnetospheric source region of discrete auroras inferred from their relationship with isotropy boundaries of energetic particles

1997 ◽  
Vol 15 (8) ◽  
pp. 943-958 ◽  
Author(s):  
A. G. Yahnin ◽  
V. A. Sergeev ◽  
B. B. Gvozdevsky ◽  
S. Vennerstrøm
Keyword(s):  
Magnetic Field ◽  
Source Region ◽  
Spatial Relationship ◽  
Auroral Oval ◽  
Energetic Particles ◽  
Closed Field ◽  
Physical Conditions ◽  
Ground Observation ◽  
Field Lines ◽  
Auroral Arcs

Abstract. According to observations, the discrete auroral arcs can sometimes be found, either deep inside the auroral oval or at the poleward border of the wide (so-called double) auroral oval, which map to very different regions of the magnetotail. To find common physical conditions for the auroral-arc generation in these magnetotail regions, we study the spatial relationship between the diffuse and discrete auroras and the isotropic boundaries (IBs) of the precipitating energetic particles which can be used to characterise locally the equatorial magnetic field in the tail. From comparison of ground observation of auroral forms with meridional profiles of particle flux measured simultaneously by the low-altitude NOAA satellites above the ground observation region, we found that (1) discrete auroral arcs are always situated polewards from (or very close to) the IB of >30-keV electrons, whereas (2) the IB of the >30-keV protons is often seen inside the diffuse aurora. These relationships hold true for both quiet and active (substorm) conditions in the premidnight-nightside (18-01-h) MLT sector considered. In some events the auroral arcs occupy a wide latitudinal range. The most equatorial of these arcs was found at the poleward edge of the diffuse auroras (but anyway in the vicinity of the electron IB), the most poleward arcs were simultaneously observed on the closed field lines near the polar-cap boundary. These observations disagree with the notion that the discrete aurora originate exclusively in the near-Earth portion of plasma sheet or exclusively on the PSBL field lines. Result (1) may imply a fundamental feature of auroral-arc formation: they originate in the current-sheet regions having very curved and tailward-stretched magnetic field lines.

scholarly journals Multiple current sheets in a double auroral oval observed from the MAGION-2 and MAGION-3 satellites

1997 ◽  
Vol 15 (4) ◽  
pp. 412-423 ◽  
Author(s):  
M. Echim ◽  
M. Ciobanu ◽  
O. Balan ◽  
A. Blagau ◽  
O. Marghitu ◽  
...  
Keyword(s):  
Recovery Phase ◽  
Auroral Oval ◽  
Magnetic Activity ◽  
Small Scale ◽  
Current Sheets ◽  
Late Recovery ◽  
Early Growth Phase ◽  
Auroral Arcs ◽  
Auroral Current ◽  
Upward Current

Abstract. A case is described of multiple current sheets crossed by the MAGION-2 satellite in the near-midnight quieting auroral oval. The data were obtained by the magnetometer experiment onboard. Results show during a quieting period after a preceding substorm, or during an early growth phase of the next substorm, two double-sheet current bands, POLB and EQUB, located at respectively the polar and equatorial borders of the auroral oval separated by about 500 km in latitude. This is consistent with the double-oval structure during recovery introduced by Elphinstone et al. (1995). Within the POLB, the magnetic field data show simultaneous existence of several narrow parallel bipolar current sheets within the upward current branch (at 69.5–70.3° invariant latitude) with an adjacent downward current branch at its polar side at (70.5–71.3°). The EQUB was similarly stratified and located at 61.2–63.5° invariant latitude. The narrow current sheets were separated on average by about 35 km and 15 km, respectively, within the POLB and EQUB. A similar case of double-oval current bands with small-scale structuring of their upward current branches during a quieting period is found in the data from the MAGION-3 satellite. These observations contribute to the double-oval structure of the late recovery phase, and add a small-scale structuring of the upward currents producing the auroral arcs in the double- oval pattern, at least for the cases presented here. Other observations of multiple auroral current sheets and theories of auroral arc multiplicity are briefly discussed. It is suggested that multiple X-lines in the distant tail, and/or leakage of energetic particles and FA currents from a series of plasmoids formed during preceding magnetic activity, could be one cause of highly stratified upward FA currents at the polar edge of the quieting double auroral oval.

scholarly journals Filamentary field-aligned currents at the polar cap region during northward interplanetary magnetic field derived with the Swarm constellation

2016 ◽  
Vol 34 (10) ◽  
pp. 901-915 ◽  
Author(s):  
Hermann Lühr ◽  
Tao Huang ◽  
Simon Wing ◽  
Guram Kervalishvili ◽  
Jan Rauberg ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Interplanetary Magnetic Field ◽  
Initial Study ◽  
Auroral Oval ◽  
Closed Field ◽  
Defense Meteorological Satellite Program ◽  
Field Lines ◽  
Auroral Arcs ◽  
First Time ◽  
Meteorological Satellite

Abstract. ESA's Swarm constellation mission makes it possible for the first time to determine field-aligned currents (FACs) in the ionosphere uniquely. In particular at high latitudes, the dual-satellite approach can reliably detect some FAC structures which are missed by the traditional single-satellite technique. These FAC events occur preferentially poleward of the auroral oval and during times of northward interplanetary magnetic field (IMF) orientation. Most events appear on the nightside. They are not related to the typical FAC structures poleward of the cusp, commonly termed NBZ. Simultaneously observed precipitating particle spectrograms and auroral images from Defense Meteorological Satellite Program (DMSP) satellites are consistent with the detected FACs and indicate that they occur on closed field lines mostly adjacent to the auroral oval. We suggest that the FACs are associated with Sun-aligned filamentary auroral arcs. Here we introduce in an initial study features of the high-latitude FAC structures which have been observed during the early phase of the Swarm mission. A more systematic survey over longer times is required to fully characterize the so far undetected field aligned currents.

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)

Longitudinal Gradients in Field-Aligned Currents as Observed by Swarm

2020 ◽  
Author(s):  
Octav Marghitu ◽  
Adrian Blăgău ◽  
Joachim Vogt
Keyword(s):  
Large Scale ◽  
Present Report ◽  
Longitudinal Direction ◽  
Auroral Oval ◽  
Activity Level ◽  
Magnetic Field Data ◽  
Swarm Satellites ◽  
Longitudinal Gradients ◽  
Operational Phase ◽  
Auroral Arcs

&lt;p&gt;Field-aligned currents (FACs) are closely related to aurora and a key component of the magnetosphere-ionosphere-thermosphere system. Large scale FAC structures, like Region 1 / Region 2, threading the whole auroral oval, as well as smaller scale FACs, associated with auroral arcs, are often assumed to consists of upward / downward current sheet pairs, uniform in longitudinal direction. While such a uniformity is consistent with the prevalent 1D symmetry of the auroral arcs and oval, longitudinal gradients may develop at times, for example when the 1D symmetry prepares to break, during the growth phase of auroral substorms. The Swarm mission provides optimum conditions to explore systematically longitudinal gradients in FACs, namely a proper spacecraft configuration, with the Swarm A / Swarm C pair lining up periodically with Swarm B at auroral latitudes, and high quality magnetic field data. The present report concentrates on a set of auroral events observed by the Swarm satellites, in this suitable configuration, during the first six months of the mission operational phase. At that time, the distance between Swarm A / Swarm C and Swarm B was in the range of a few 100 km, comparable to the length scale of electrojet currents associated with auroral arcs. Not surprising, longitudinal gradients in FACs are occasionally significant, a feature which is discussed with respect to the location, activity level, and substorm phase of the event.&lt;/p&gt;

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