scholarly journals Astrid-2 and ground-based observations of the auroral bulge in the middle of the nightside convection throat

2001 ◽  
Vol 19 (6) ◽  
pp. 633-641 ◽  
Author(s):  
G. T. Marklund ◽  
T. Karlsson ◽  
P. Eglitis ◽  
H. Opgenoorth
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Large Scale ◽  
Current Model ◽  
Energetic Electron ◽  
Auroral Oval ◽  
Plasma Convection ◽  
Magnetometer Data ◽  
Electric Fields And Currents ◽  
Good Agreement

Abstract. Results concerning the electrodynamics of the nightside auroral bulge are presented based on simultaneous satellite and ground-based observations. The satellite data include Astrid-2 measurements of electric fields, currents and particles from a midnight auroral oval crossing and Polar UVI images of the large-scale auroral distribution. The ground-based observations include STARE and SuperDARN electric fields and magnetic records from the Greenland and MIRACLE magnetometer network, the latter including stations from northern Scandinavia north to Svalbard. At the time of the Astrid-2 crossing the ground-based data reveal intense electrojet activity, both to the east and west of the Astrid-2 trajectory, related to the Polar observations of the auroral bulge but not necessarily to a typical substorm. The energetic electron fluxes measured by Astrid-2 across the auroral oval were generally weak being consistent with a gap observed in the auroral luminosity distribution. The electric field across the oval was directed westward, intensifying close to the poleward boundary followed by a decrease in the polar cap. The combined observations suggests that Astrid-2 was moving close to the separatrix between the dusk and dawn convection cells in a region of low conductivity. The constant westward direction of the electric field across the oval indicates that current continuity was maintained, not by polarisation electric fields (as in a Cowling channel), but solely by localized up- and downward field-aligned currents in good agreement with the Astrid-2 magnetometer data. The absence of a polarisation electric field and thus of an intense westward closure current between the dawn and dusk convection cells is consistent with the relatively weak precipitation and low conductivity in the convection throat. Thus, the Cowling current model is not adequate for describing the electrodynamics of the nightside auroral bulge treated here.Key words. Ionosphere (auroral ionosphere; electric fields and currents; plasma convection)

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 Transpolar arc evolution and associated potential patterns

2004 ◽  
Vol 22 (4) ◽  
pp. 1213-1231 ◽  
Author(s):  
J. A. Cumnock ◽  
L. G. Blomberg
Keyword(s):  
Magnetic Field ◽  
Electric Fields ◽  
Polar Region ◽  
Auroral Oval ◽  
Plasma Convection ◽  
Auroral Emission ◽  
Field Aligned Current ◽  
Auroral Emissions ◽  
Institute Of Technology ◽  
Electric Fields And Currents

Abstract. We present two event studies encompassing detailed relationships between plasma convection, field-aligned current, auroral emission, and particle precipitation boundaries. We illustrate the influence of the Interplanetary Magnetic Field By component on theta aurora development by showing two events during which the theta originates on both the dawn and dusk sides of the auroral oval. Both theta then move across the entire polar region and become part of the opposite side of the auroral oval. Electric and magnetic field and precipitating particle data are provided by DMSP, while the Polar UVI instrument provides measurements of auroral emissions. Utilizing satellite data as inputs, the Royal Institute of Technology model provides the high-latitude ionospheric electrostatic potential pattern calculated at different times during the evolution of the theta aurora, resulting from a variety of field-aligned current configurations associated with the changing global aurora. Key words. Ionosphere (auroral ionosphere; electric fields and currents). Magnetospheric physics (magnetosphereionosphere interactions)

scholarly journals Mapping travelling convection vortex events with respect to energetic particle boundaries

1998 ◽  
Vol 16 (8) ◽  
pp. 891-899 ◽  
Author(s):  
T. Moretto ◽  
A. Yahnin
Keyword(s):  
Electric Fields ◽  
Energetic Particle ◽  
Energetic Electron ◽  
High Energy ◽  
Electron Trapping ◽  
Particle Measurements ◽  
High Energy Electrons ◽  
Precipitation Boundary ◽  
Magnetometer Data ◽  
Electric Fields And Currents

Abstract. Thirteen events of high-latitude ionospheric travelling convection vortices during very quiet conditions were identified in the Greenland magnetometer data during 1990 and 1991. The latitudes of the vortex centres for these events are compared to the energetic electron trapping boundaries as identified by the particle measurements of the NOAA 10 satellite. In addition, for all events at least one close DMSP overpass was available. All but one of the 13 cases agree to an exceptional degree that: the TCV centres are located within the region of trapped, high energy electrons close to the trapping boundary for the population of electrons with energy greater than >100 keV. Correspondingly, from the DMSP data they are located within the region of plasmasheet-type precipitation close to the CPS/BPS precipitation boundary. That is, the TCV centres map to deep inside the magnetosphere and not to the magnetopause.Key Words. Ionosphere (Electric fields and currents; Particle precipitation) · Magnetospheric physics (Magnetosphere-ionosphere interaction)

scholarly journals Auroral E-region electron density height profile modificationby electric field driven vertical plasma transport:some evidence in EISCAT CP-1 data statistics

2004 ◽  
Vol 22 (3) ◽  
pp. 901-910 ◽  
Author(s):  
T. Bösinger ◽  
G. C. Hussey ◽  
C. Haldoupis ◽  
K. Schlegel
Keyword(s):  
Electric Field ◽  
Electron Density ◽  
Electric Fields ◽  
Plasma Transport ◽  
Plasma Convection ◽  
Ionosphere Plasma ◽  
E Region ◽  
Eiscat Radar ◽  
Electric Fields And Currents ◽  
Electron Density Profiles

Abstract. A model developed several years ago by Huuskonen et al. (1984) predicted that vertical transport of ions in the nocturnal auroral E-region ionosphere can shift the electron density profiles in altitude during times of sufficiently large electric fields. If the vertical plasma transport effect was to operate over a sufficiently long enough time, then the real height of the E-region electron maximum should be shifted some km upwards (downwards) in the eastward (westward) auroral electrojet, respectively, when the electric field is strong, exceeding, say, 50 mV/m. Motivated by these predictions and the lack of any experimental verification so far, we made use of the large database of the European Incoherent Scatter (EISCAT) radar to investigate if the anticipated vertical plasma transport is at work in the auroral E-region ionosphere and thus to test the Huuskonen et al. (1984) model. For this purpose a new type of EISCAT data display was developed which enabled us to order a large number of electron density height profiles, collected over 16 years of EISCAT operation, according to the electric field magnitude and direction as measured at the same time at the radar's magnetic field line in the F-region. Our analysis shows some signatures in tune with a vertical plasma transport in the auroral E-region of the type predicted by the Huuskonen et al. model. The evidence brought forward is, however, not unambiguous and requires more rigorous analysis. Key words. Ionosphere (auroral ionosphere; plasma convection; electric fields and currents)

scholarly journals Simultaneous optical, CUTLASS HF radar, and FAST spacecraft observations: signatures of boundary layer processes in the cusp

2004 ◽  
Vol 22 (2) ◽  
pp. 511-525 ◽  
Author(s):  
K. Oksavik ◽  
F. Søraas ◽  
J. Moen ◽  
R. Pfaff ◽  
J. A. Davies ◽  
...  
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Broad Band ◽  
Spectral Width ◽  
Hf Radar ◽  
Optical Data ◽  
Low Energy Electrons ◽  
Field Lines ◽  
Auroral Phenomena ◽  
Electric Fields And Currents

Abstract. In this paper we discuss counterstreaming electrons, electric field turbulence, HF radar spectral width enhancements, and field-aligned currents in the southward IMF cusp region. Electric field and particle observations from the FAST spacecraft are compared with CUTLASS Finland spectral width enhancements and ground-based optical data from Svalbard during a meridional crossing of the cusp. The observed 630nm rayed arc (Type-1 cusp aurora) is associated with stepped cusp ion signatures. Simultaneous counterstreaming low-energy electrons on open magnetic field lines lead us to propose that such electrons may be an important source for rayed red arcs through pitch angle scattering in collisions with the upper atmosphere. The observed particle precipitation and electric field turbulence are found to be nearly collocated with the equatorward edge of the optical cusp, in a region where CUTLASS Finland also observed enhanced spectral width. The electric field turbulence is observed to extend far poleward of the optical cusp. The broad-band electric field turbulence corresponds to spatial scale lengths down to 5m. Therefore, we suggest that electric field irregularities are directly responsible for the formation of HF radar backscatter targets and may also explain the observed wide spectra. FAST also encountered two narrow highly structured field-aligned current pairs flowing near the edges of cusp ion steps. Key words. Ionosphere (electric fields and currents). Magnetosphere physics (magnetopause, cusp, and boundary layers; auroral phenomena)

scholarly journals A statistical study of intense electric fields at 4−7 R<sub><i>E</i></sub> geocentric distance using Cluster

2005 ◽  
Vol 23 (7) ◽  
pp. 2579-2588 ◽  
Author(s):  
T. Johansson ◽  
T. Karlsson ◽  
G. Marklund ◽  
S. Figueiredo ◽  
P.-A. Lindqvist ◽  
...  
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Time Distribution ◽  
Statistical Study ◽  
Auroral Oval ◽  
Field Structure ◽  
Geocentric Distance ◽  
Using Data ◽  
Auroral Phenomena ◽  
Current Systems

Abstract. Intense high-latitude electric fields (>150 mV/m mapped to ionospheric altitude) at 4–7 RE geocentric distance have been investigated in a statistical study, using data from the Cluster satellites. The orbit of the Cluster satellites limits the data collection at these altitudes to high latitudes, including the poleward part of the auroral oval. The occurrence and distribution of the selected events have been used to characterize the intense electric fields and to investigate their dependance on parameters such as MLT, CGLat, altitude, and also Kp. Peaks in the local time distribution are found in the evening to morning sectors but also in the noon sector, corresponding to cusp events. The electric field intensities decrease with increasing latitude in the region investigated (above 60 CGLat). A dependence on geomagnetic activity is indicated since the probability of finding an event increases up to Kp=5–6. The scales sizes are in the range up to 10 km (mapped to ionospheric altitude) with a maximum around 4–5km, consistent with earlier findings at lower altitudes and Cluster event studies. The magnitudes of the electric fields are inversely proportional to the scale sizes. The type of electric field structure (convergent or divergent) is consistent with the FAC direction for a subset of events with electric field intensities in the range 500–1000 mV/m and with clear bipolar signatures. The FAC directions are also consistent with the Region 1 and NBZ current systems, the latter of which prevail only during northward IMF conditions. For scale sizes less than 2 km the majority of the events were divergent electric field structures. Both converging and diverging electric fields were found throughout the investigated altitude range (4–7 RE geocentric distance). Keywords. Magnetospheric physics (Electric fields; Auroral phenomena; Magnetosphere-ionosphere interactions)

The Electric Field Measuring by Phase Selective Photoreflectance

1996 ◽  
Vol 421 ◽  
Author(s):  
J. S. Hwang ◽  
W. Y. Chou ◽  
S. L. Tyan ◽  
Y. C. Wang ◽  
H. Shen
Keyword(s):  
Electric Field ◽  
Theoretical Calculation ◽  
Buffer Layer ◽  
Electric Fields ◽  
Phase Angle ◽  
Substrate Interface ◽  
Field Measuring ◽  
Lock In ◽  
Good Agreement ◽  
Reference Phase

AbstractThe built-in electric fields in a MBE grown δ-doped GaAs homojunction have been investigated by the techniques of photoreflectance and phase suppression. Two Franz-Keldysh oscillation features originating from two different fields in the structure superimpose with each other in the photoreflectance spectrum. By properly selecting the reference phase of the lock-in amplifier, one of the features can be suppressed, thus enabling us to determine the electric fields from two different regions. We have demonstrated that only two PR spectra, in-phase and outphase components, are needed to find the phase angle which suppresses one of the features. The electric field in the top layer is 3.5 ± 0.2 × 105 V/cm, which is in good agreement with theoretical calculation. The electric field in the buffer layer is 1.2 ± 0.1 × 104 V/cm, which suggests the existence of interface states at the buffer/substrate interface.

scholarly journals The dawn and dusk electrojet response to substorm onset

2000 ◽  
Vol 18 (9) ◽  
pp. 1097-1107 ◽  
Author(s):  
E. Borälv ◽  
P. Eglitis ◽  
H. J. Opgenoorth ◽  
E. Donovan ◽  
G. Reeves ◽  
...  
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Information Transfer ◽  
Neutral Line ◽  
Substorm Onset ◽  
Model Case ◽  
Onset Timing ◽  
Storms And Substorms ◽  
Electric Fields And Currents ◽  
Substorm Onsets

Abstract. We have investigated the time delay between substorm onset and related reactions in the dawn and dusk ionospheric electrojets, clearly separated from the nightside located substorm current wedge by several hours in MLT. We looked for substorm onsets occurring over Greenland, where the onset was identified by a LANL satellite and DMI magnetometers located on Greenland. With this setup the MARIA magnetometer network was located at dusk, monitoring the eastward electrojet, and the IMAGE chain at dawn, for the westward jet. In the first few minutes following substorm onset, sudden enhancements of the electrojets were identified by looking for rapid changes in magnetograms. These results show that the speed of information transfer between the region of onset and the dawn and dusk ionosphere is very high. A number of events where the reaction seemed to preceed the onset were explained by either unfavorable instrument locations, preventing proper onset timing, or by the inner magnetosphere's reaction to the Earthward fast flows from the near-Earth neutral line model. Case studies with ionospheric coherent (SuperDARN) and incoherent (EISCAT) radars have been performed to see whether a convection-induced electric field or enhanced conductivity is the main agent for the reactions in the electrojets. The results indicate an imposed electric field enhancement.Key words: Ionosphere (auroral ionosphere; electric fields and currents) - Magnetospheric physics (storms and substorms)

ELECTRIC FIELD INFLUENCE ON TRAVELING WAVE PROPAGATION AND STATIONARY PATTERN FORMATION

1995 ◽  
Vol 05 (03) ◽  
pp. 797-807 ◽  
Author(s):  
J. MOSQUERA ◽  
M. GÓMEZ-GESTEIRA ◽  
V. PÉREZ-MUÑUZURI ◽  
A.P. MUÑUZURI ◽  
V. PÉREZ-VILLAR
Keyword(s):  
Wave Propagation ◽  
Pattern Formation ◽  
Electric Field ◽  
Electric Fields ◽  
Traveling Wave ◽  
Traveling Fronts ◽  
Spatial Terms ◽  
Oregonator Model ◽  
Field Influence ◽  
Good Agreement

The electric field influence on pattern formation and traveling wave propagation is investigated in the framework of the Oregonator model. When an electric field is applied to a system that can suffer spatial instabilities, Turing and Turing-like patterns (traveling fronts that become stationary patterns when reaching a zero-flux boundary) are observed. On the other hand, when an electric field is applied to a system that cannot become unstable by spatial terms and where wavefronts are propagating in the absence of electric fields, the velocity of these wavefronts is modified and can even be reversed. This is in good agreement with previous experimental results.

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