scholarly journals On auroral dynamics observed by HF radar: 1. Equatorward edge of the afternoon-evening diffuse luminosity belt

2000 ◽  
Vol 18 (12) ◽  
pp. 1560-1575 ◽  
Author(s):  
M. Uspensky ◽  
P. Eglitis ◽  
H. Opgenoorth ◽  
G. Starkov ◽  
T. Pulkkinen ◽  
...  
Keyword(s):  
Electron Plasma ◽  
Auroral Oval ◽  
Hf Radar ◽  
Phase Development ◽  
Evening Sector ◽  
Density Enhancement ◽  
Late Evening ◽  
Eiscat Radar ◽  
Auroral Phenomena ◽  
Diurnal Rotation

Abstract. Observations and modelling are presented which illustrate the ability of the Finland CUTLASS HF radar to monitor the afternoon-evening equatorward auroral boundary during weak geomagnetic activity. The subsequent substorm growth phase development was also observed in the late evening sector as a natural continuation of the preceding auroral oval dynamics. Over an 8 h period the CUTLASS Finland radar observed a narrow (in range) and persistent region of auroral F- and (later) E-layer echoes which gradually moved equatorward, consistent with the auroral oval diurnal rotation. This echo region corresponds to the subvisual equatorward edge of the diffuse luminosity belt (SEEL) and the ionospheric footprint of the inner boundary of the electron plasma sheet. The capability of the Finland CUTLASS radar to monitor the E-layer SEEL-echoes is a consequence of the nearly zero E-layer rectilinear aspect angles in a region 5–10° poleward of the radar site. The F-layer echoes are probably the boundary blob echoes. The UHF EISCAT radar was in operation and observed a similar subvisual auroral arc and an F-layer electron density enhancement when it appeared in its antenna beam.Key words: Ionsophere (ionospheric irregularities) · Magnetospheric physics (auroral phenomena; magnetosphere–ionosphere interactions)

scholarly journals Observations of an auroral streamer in a double oval configuration

2011 ◽  
Vol 29 (4) ◽  
pp. 701-716 ◽  
Author(s):  
O. Amm ◽  
R. Nakamura ◽  
T. Takada ◽  
K. Kauristie ◽  
H. U. Frey ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Recovery Phase ◽  
Auroral Oval ◽  
Expansion Phase ◽  
Optical Instruments ◽  
Image Satellite ◽  
Bursty Bulk Flow ◽  
Polarization Electric Field ◽  
Late Evening ◽  
Eiscat Radar

Abstract. During the late evening and night of 14 September 2004, the nightside auroral oval shows a distinct double oval configuration for several hours after a substorm onset at ~18:45 UT. This structure is observed both by the IMAGE satellite optical instruments focusing on the Southern Hemisphere, and by the MIRACLE ground-based instrument network in Scandinavia. At ~21:17 UT during the recovery phase of the substorm, an auroral streamer is detected by these instruments and the EISCAT radar, while simultaneously the Cluster satellites observe a bursty bulk flow in the conjugate portion of the plasma sheet in the magnetotail. Our combined data analysis reveals significant differences between the ionospheric equivalent current signature of this streamer within a double oval configuration, as compared to previously studied streamer events without such a configuration. We attribute these differences to the presence of an additional poleward polarization electric field between the poleward and the equatorward portions of the double oval, and show with a simple model that such an assumption can conceptually explain the observations. Further, we estimate the total current transferred in meridional direction by this recovery phase streamer to ~80 kA, significantly less than for previously analysed expansion phase streamer events. Both results indicate that the development of auroral streamers is dependent on the ambient background conditions in the magnetosphere-ionosphere system. The auroral streamer event studied was simultaneously observed in the conjugate Northern and Southern Hemisphere ionosphere.

scholarly journals Remote sensing of the proton aurora characteristics from IMAGE-FUV

2003 ◽  
Vol 21 (11) ◽  
pp. 2165-2173 ◽  
Author(s):  
D. V. Bisikalo ◽  
V. I. Shematovich ◽  
J.-C. Gérard ◽  
M. Meurant ◽  
S. B. Mende ◽  
...  
Keyword(s):  
Imaging System ◽  
Wide Band ◽  
Auroral Oval ◽  
The North ◽  
Evening Sector ◽  
North Polar ◽  
Auroral Phenomena ◽  
Proton Aurora ◽  
Good Agreement

Abstract. The combination of simultaneous global images of the north polar region obtained with the IMAGE-FUV imaging system makes it possible to globally map the properties of the electron and proton auroral precipitation. The SI12 imager, which observes the Doppler-shifted Lyman-a emission, provides a global snapshot of the proton aurora every 2 min. These images may be combined with those from the Wide-band Imaging Camera (WIC), to remotely characterize the proton precipitation in proton-dominated auroral structures frequently observed in the afternoon and pre-midnight sectors at the equatorial edge of the auroral oval. It is shown that both the proton energy flux and the mean energy determined by this method are in good agreement with coincident in situ measurement from low altitude satellites carrying proton detectors, when taking into account the different spatial resolution of the two types of observations. Four proton-dominated cases are illustrated in this study. They belong to two categories of proton auroral features: (i) hydrogen arcs known to occur in the evening sector equatorward of the electron oval and (ii) detached proton arcs observed with IMAGE-FUV in the afternoon sector following changes in orientation of the interplanetary magnetic field. They are characterized by a proton flux of 0.5–2 mWm-2 and a mean energy in the range 10–17 keV.Key words. Magnetospheric physics (auroral phenomena; energetic particles, precipitating; magnetopause, cusp, arid boundary layers)

scholarly journals ESR and EISCAT observations of the response of the cusp and cleft to IMF orientation changes

2000 ◽  
Vol 18 (9) ◽  
pp. 1009-1026 ◽  
Author(s):  
I. W. McCrea ◽  
M. Lockwood ◽  
J. Moen ◽  
F. Pitout ◽  
P. Eglitis ◽  
...  
Keyword(s):  
Large Scale ◽  
Initial Conditions ◽  
Plasma Temperature ◽  
Radar Data ◽  
Auroral Oval ◽  
Hf Radar ◽  
High Electron ◽  
Vhf Radar ◽  
Ionosphere Plasma ◽  
Main Cusp

Abstract. We report observations of the cusp/cleft ionosphere made on December 16th 1998 by the EISCAT (European incoherent scatter) VHF radar at Tromsø and the EISCAT Svalbard radar (ESR). We compare them with observations of the dayside auroral luminosity, as seen by meridian scanning photometers at Ny Ålesund and of HF radar backscatter, as observed by the CUTLASS radar. We study the response to an interval of about one hour when the interplanetary magnetic field (IMF), monitored by the WIND and ACE spacecraft, was southward. The cusp/cleft aurora is shown to correspond to a spatially extended region of elevated electron temperatures in the VHF radar data. Initial conditions were characterised by a northward-directed IMF and cusp/cleft aurora poleward of the ESR. A strong southward turning then occurred, causing an equatorward motion of the cusp/cleft aurora. Within the equatorward expanding, southward-IMF cusp/cleft, the ESR observed structured and elevated plasma densities and ion and electron temperatures. Cleft ion fountain upflows were seen in association with elevated ion temperatures and rapid eastward convection, consistent with the magnetic curvature force on newly opened field lines for the observed negative IMF By. Subsequently, the ESR beam remained immediately poleward of the main cusp/cleft and a sequence of poleward-moving auroral transients passed over it. After the last of these, the ESR was in the polar cap and the radar observations were characterised by extremely low ionospheric densities and downward field-aligned flows. The IMF then turned northward again and the auroral oval contracted such that the ESR moved back into the cusp/cleft region. For the poleward-retreating, northward-IMF cusp/cleft, the convection flows were slower, upflows were weaker and the electron density and temperature enhancements were less structured. Following the northward turning, the bands of high electron temperature and cusp/cleft aurora bifurcated, consistent with both subsolar and lobe reconnection taking place simultaneously. The present paper describes the large-scale behaviour of the ionosphere during this interval, as observed by a powerful combination of instruments. Two companion papers, by Lockwood et al. (2000) and Thorolfsson et al. (2000), both in this issue, describe the detailed behaviour of the poleward-moving transients observed during the interval of southward Bz, and explain their morphology in the context of previous theoretical work.Key words: Ionosphere (ionosphere - magnetosphere interactions; auroral ionosphere; plasma temperature and density)

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)

scholarly journals Middle-energy electron anisotropies in the auroral region

2004 ◽  
Vol 22 (1) ◽  
pp. 237-249 ◽  
Author(s):  
P. Janhunen ◽  
A. Olsson ◽  
H. Laakso ◽  
A. Vaivads
Keyword(s):  
Electron Distribution ◽  
Electron Flow ◽  
High Mobility ◽  
High Energy ◽  
Auroral Oval ◽  
Distribution Functions ◽  
Particle Interactions ◽  
Latitude Distribution ◽  
Field Lines ◽  
Auroral Phenomena

Abstract. Field-aligned anisotropic electron distribution functions of T∥ > T⊥ type are observed on auroral field lines at both low and high altitudes. We show that typically the anisotropy is limited to a certain range of energies, often below 1keV, although sometimes extending to slightly higher energies as well. Almost always there is simultaneously an isotropic electron distribution at higher energies. Often the anisotropies are up/down symmetrical, although cases with net upward or downward electron flow also occur. For a statistical analysis of the anisotropies we divide the energy range into low (below 100eV), middle (100eV–1keV) and high (above 1keV) energies and develop a measure of anisotropy expressed in density units. The statistical magnetic local time and invariant latitude distribution of the middle-energy anisotropies obeys that of the average auroral oval, whereas the distributions of the low and high energy anisotropies are more irregular. This suggests that it is specifically the middle-energy anisotropies that have something to do with auroral processes. The anisotropy magnitude decreases monotonically with altitude, as one would expect, because electrons have high mobility along the magnetic field and thus, the anisotropy properties spread rapidly to different altitudes. Key words. Magnetospheric physics (auroral phenomena). Space plasma physics (wave-particle interactions; changed particle motion and acceleration)

Electrodynamic structure of the late evening sector of the auroral zone

1980 ◽  
Vol 85 (A3) ◽  
pp. 1179-1193 ◽  
Author(s):  
W.J. Burke ◽  
D.A. Hardy ◽  
F.J. Rich ◽  
M.C. Kelley ◽  
M. Smiddy ◽  
...  
Keyword(s):  
Auroral Zone ◽  
Evening Sector ◽  
Late Evening ◽  
Electrodynamic Structure

scholarly journals Effects of solar wind density on auroral electrojets and brightness under influence of substorms

2009 ◽  
Vol 27 (1) ◽  
pp. 113-119 ◽  
Author(s):  
J.-H. Shue ◽  
Y. Kamide ◽  
J. W. Gjerloev
Keyword(s):  
Solar Wind ◽  
Auroral Oval ◽  
Auroral Electrojet ◽  
The Other ◽  
Auroral Ionosphere ◽  
Stored Energy ◽  
Solar Wind Density ◽  
The Earth ◽  
Density Enhancement ◽  
Solar Wind Parameters

Abstract. Using the auroral electrojet indices and Polar Ultraviolet Imager auroral images, we examined two fortuitous events during which the solar wind density had clear enhancements while the other solar wind parameters were relatively constant. Two electrojet enhancements were found in each event. The first electrojet enhancement was likely to be related to a substorm in which an auroral bulge appeared at premidnight. The second electrojet enhancement was driven by the density enhancement in the solar wind. The auroral oval became wider in latitude and the auroral distribution became dispersed after the density enhancement arrived at the Earth. The total auroral power integrated over the entire nightside region from 50 to 80° MLAT, however, did not increase significantly in response to the density enhancement. Our interpretation is that the substorm that occurred prior to the solar wind density enhancement had drained out a significant portion of the stored energy in the magnetotail; therefore, less precipitation energy was deposited into the auroral ionosphere by the density enhancement.

scholarly journals Swarm Satellite and EISCAT Radar Observations of a Plasma Flow Channel in the Auroral Oval Near Magnetic Midnight

2018 ◽  
Vol 123 (6) ◽  
pp. 5140-5158 ◽  
Author(s):  
A. T. Aikio ◽  
H. Vanhamäki ◽  
A. B. Workayehu ◽  
I. I. Virtanen ◽  
K. Kauristie ◽  
...  
Keyword(s):  
Plasma Flow ◽  
Auroral Oval ◽  
Flow Channel ◽  
Radar Observations ◽  
Eiscat Radar ◽  
Swarm Satellite

scholarly journals Ps 6 disturbances: relation to substorms and the auroral oval

2003 ◽  
Vol 21 (2) ◽  
pp. 493-508 ◽  
Author(s):  
M. Connors ◽  
G. Rostoker ◽  
G. Sofko ◽  
R. L. McPherron ◽  
M. G. Henderson
Keyword(s):  
Time Delay ◽  
Electric Fields ◽  
Onset Time ◽  
Radar Data ◽  
Recovery Phase ◽  
Auroral Oval ◽  
Hf Radar ◽  
Mhd Waves ◽  
First Case ◽  
Relationship Of

Abstract. Ps 6 disturbances and associated omega bands are often considered to be part of the phenomenology of the recovery phase of substorms. We note cases of the initiation of Ps 6 activity at or very near the time of onset, either of a substorm expansive phase, a pseudobreakup, or a poleward border intensification. Thus, we claim that Ps 6 disturbances need not be viewed primarily as phenomena of the recovery phase. This produces both the challenge of explaining Ps 6 within a broader context and the opportunity to use Ps 6 observations to better understand magnetospheric phenomenology, including expansive phase onsets. We further examine the position of the causative currents for Ps 6 and find that they may be located at either the equatorward or poleward border of the auroral oval, or within it. In the first case, the relationship of expansive phase onset and time delay to Ps 6 initiation appears to be very short. In the latter case, there is an association with poleward border intensification, but with a measurable time delay. We present HF radar data to discuss how the electric field at onset time favors the growth of Ps 6 current systems.Key words. Magnetospheric physics (Storms and substorms; Electric fields; MHD waves and instabilities)

Sign in / Sign up

Export Citation Format

Share Document