scholarly journals Signatures of moving polar cap arcs in the F-region PolarDARN echoes

2012 ◽  
Vol 30 (3) ◽  
pp. 441-455 ◽  
Author(s):  
A. V. Koustov ◽  
K. Hosokawa ◽  
N. Nishitani ◽  
K. Shiokawa ◽  
H. Liu
Keyword(s):  
Spectral Width ◽  
Global Scale ◽  
Auroral Oval ◽  
Polar Cap ◽  
Common Features ◽  
F Region ◽  
Radar Network ◽  
Radar Measurements ◽  
Resolute Bay ◽  
Region Plasma

Abstract. Joint observations of the all-sky camera at Resolute Bay (Nunavut, Canada) and the Polar Dual Auroral Radar Network (PolarDARN) HF radars at Rankin Inlet and Inuvik (Canada) are considered to establish radar signatures of poleward moving polar cap arcs "detaching" from the auroral oval. Common features of the events considered are enhanced power or echo occurrence in the wake of the arcs and enhanced spectral width of these echoes. When the arcs were oriented along some of the radar beams, velocity reversals at the arc location were observed with the directions of the arc-associated flows corresponding to a converging electric field. For the event of 9 December 2007, two arcs were poleward progressing almost along the central beams of the Inuvik radar at the speed close to the E × B drift of the bulk of the F-region plasma as inferred from HF Doppler velocities and from independent measurements by the Resolute Bay ionosonde. In global-scale convection maps inferred from all Super Dual Auroral Radar Network (SuperDARN) radar measurements, the polar cap arcs were often seen close to the reversal line of additional mesoscale convection cells located poleward of the normal cells related to the auroral oval.

scholarly journals A Statistical study of the Doppler spectral width of high-latitude ionospheric F-region echoes recorded with SuperDARN coherent HF radars

2002 ◽  
Vol 20 (11) ◽  
pp. 1769-1781 ◽  
Author(s):  
J.-P. Villain ◽  
R. André ◽  
M. Pinnock ◽  
R. A. Greenwald ◽  
C. Hanuise
Keyword(s):  
High Latitude ◽  
Statistical Study ◽  
Spectral Width ◽  
Auroral Oval ◽  
F Region ◽  
Radar Network ◽  
Period 2 ◽  
Time Period ◽  
High Latitude Ionosphere ◽  
Data Points

Abstract. The HF radars of the Super Dual Auroral Radar Network (SuperDARN) provide measurements of the E × B drift of ionospheric plasma over extended regions of the high-latitude ionosphere. We have conducted a statistical study of the associated Doppler spectral width of ionospheric F-region echoes. The study has been conducted with all available radars from the Northern Hemisphere for 2 specific periods of time. Period 1 corresponds to the winter months of 1994, while period 2 covers October 1996 to March 1997. The distributions of data points and average spectral width are presented as a function of Magnetic Latitude and Magnetic Local Time. The databases are very consistent and exhibit the same features. The most stringent features are: a region of very high spectral width, collocated with the ionospheric LLBL/cusp/mantle region; an oval shaped region of high spectral width, whose equator-ward boundary matches the poleward limit of the Holzworth and Meng auroral oval. A simulation has been conducted to evaluate the geometrical and instrumental effects on the spectral width. It shows that these effects cannot account for the observed spectral features. It is then concluded that these specific spectral width characteristics are the signature of ionospheric/magnetospheric coupling phenomena.Key words. Ionosphere (auroral ionosphere; ionosphere-magnetosphere interactions; ionospheric irregularities)

scholarly journals EISCAT and Cluster observations in the vicinity of the dynamical polar cap boundary

2008 ◽  
Vol 26 (1) ◽  
pp. 87-105 ◽  
Author(s):  
A. T. Aikio ◽  
T. Pitkänen ◽  
D. Fontaine ◽  
I. Dandouras ◽  
O. Amm ◽  
...  
Keyword(s):  
Neutral Line ◽  
Broad Band ◽  
Low Frequency ◽  
Recovery Phase ◽  
Auroral Oval ◽  
Polar Cap ◽  
Early Recovery ◽  
F Region ◽  
Cluster Data ◽  
Cluster Satellite

Abstract. The dynamics of the polar cap boundary and auroral oval in the nightside ionosphere are studied during late expansion and recovery of a substorm from the region between Tromsø (66.6° cgmLat) and Longyearbyen (75.2° cgmLat) on 27 February 2004 by using the coordinated EISCAT incoherent scatter radar, MIRACLE magnetometer and Cluster satellite measurements. During the late substorm expansion/early recovery phase, the polar cap boundary (PCB) made zig-zag-type motion with amplitude of 2.5° cgmLat and period of about 30 min near magnetic midnight. We suggest that the poleward motions of the PCB were produced by bursts of enhanced reconnection at the near-Earth neutral line (NENL). The subsequent equatorward motions of the PCB would then represent the recovery of the merging line towards the equilibrium state (Cowley and Lockwood, 1992). The observed bursts of enhanced westward electrojet just equatorward of the polar cap boundary during poleward expansions were produced plausibly by particles accelerated in the vicinity of the neutral line and thus lend evidence to the Cowley-Lockwood paradigm. During the substorm recovery phase, the footpoints of the Cluster satellites at a geocentric distance of 4.4 RE mapped in the vicinity of EISCAT measurements. Cluster data indicate that outflow of H+ and O+ ions took place within the plasma sheet boundary layer (PSBL) as noted in some earlier studies as well. We show that in this case the PSBL corresponded to a region of enhanced electron temperature in the ionospheric F region. It is suggested that the ion outflow originates from the F region as a result of increased ambipolar diffusion. At higher altitudes, the ions could be further energized by waves, which at Cluster altitudes were observed as BBELF (broad band extra low frequency) fluctuations. The four-satellite configuration of Cluster revealed a sudden poleward expansion of the PSBL by 2° during ~5 min. The beginning of the poleward motion of the PCB was associated with an intensification of the downward FAC at the boundary. We suggest that the downward FAC sheet at the PCB is the high-altitude counterpart of the Earthward flowing FAC produced in the vicinity of the magnetotail neutral line by the Hall effect (Sonnerup, 1979) during a short-lived reconnection pulse.

Westward travelling surge driven by the polar cap flow channels

2021 ◽  
Author(s):  
Yuzhang Ma ◽  
Qing-He Zhang ◽  
Larry R. Lyons ◽  
Jiang Liu ◽  
Zan-Yang Xing ◽  
...  
Keyword(s):  
Electron Temperature ◽  
Flow Channel ◽  
Polar Cap ◽  
Temperature Plasma ◽  
F Region ◽  
Flow Channels ◽  
Bulge Region ◽  
Low Entropy ◽  
The Relationship ◽  
Region Plasma

<p>Following substorm auroral onset, the active aurora region usually expands poleward toward the poleward auroral boundary. Such poleward expansion is often associated with a bulge region that expands westward and forms the westward travelling surge (WTS). In this paper we show all-sky imager and Poker Flat Advanced Modular Incoherent Scatter Radar (PFISR) radar observations of two surge events to investigate the relationship between the surge and flow from the polar cap. For both events, we observe auroral streamers, with an adjacent flow channel consisting of decreased density and cool electron temperature plasma flowing equatorward. This flow channel appears to impinge and lead/feed surge formation, and to stay connected to the surge as it moves westward. Also, for both events, streamer observations indicate that, following initial surge development, similar flows led to explosive surge enhancements. The observation that the streamers connected to the auroral polar boundary and that the flow channels consisted of low density, low electron temperature plasma indicates that the impinging plasma came from the polar cap. For both events, the altitude variations of F region plasma within the surges are related with aurora emission and the poleward/equatorward flow, and the surges develop strong auroral streamers that initiate along the poleward auroral boundary when contacted with flow from the polar cap. These results suggest that the polar cap flow channels play a crucial role in auroral surges by feeding low entropy plasma into surge initiation and development, and also playing an important role in the dynamics within a surge.</p>

VHF and HF radar measurements of E and F region plasma drifts at the magnetic equator

1992 ◽  
Vol 97 (A3) ◽  
pp. 3011-3017 ◽  
Author(s):  
K. S. Viswanathan ◽  
S. P. Namboothiri ◽  
P. B. Rao
Keyword(s):  
Magnetic Equator ◽  
Hf Radar ◽  
F Region ◽  
Plasma Drifts ◽  
Radar Measurements ◽  
Region Plasma

scholarly journals A case study of HF radar spectra and 630.0 nm auroral emission in the pre-midnight sector

2001 ◽  
Vol 19 (3) ◽  
pp. 327-339 ◽  
Author(s):  
M. Lester ◽  
S. E. Milan ◽  
V. Besser ◽  
R. Smith
Keyword(s):  
Magnetic Field ◽  
Special Interest ◽  
Line Emission ◽  
Spectral Width ◽  
Auroral Oval ◽  
Hf Radar ◽  
Polar Cap ◽  
Particle Precipitation ◽  
The Relationship ◽  
Red Line

Abstract. A comparison of HF radar backscatter observed by the CUTLASS Finland radar, meridian scanning photometer data from Longyearbyen, magnetic field variations from IMAGE stations, and particle precipitation measured by the DMSP F12 spacecraft is presented. The interval under discussion occurred in the pre-midnight local time sector, during a period of weakly northward interplanetary magnetic field. A region of HF backscatter, typically 8 degrees wide, occurred in the field of view of the CUTLASS Finland radar. A well defined gradient in the spectral width parameter was present, with mainly low (< 200 m s - 1 ) spectral widths in the lower latitude part of the scatter and predominantly large (> 200 ms - 1 ) spectral widths in the higher latitude part. The relationship between the spectral width and the red line (630.0 nm) emission measured by the meridian scanning photometer is considered. The poleward border of the red line emission, which has, in the past, been proposed as being representative of the polar cap boundary, was co-located to within 1° of magnetic latitude with the gradient in spectral width for part of the interval. Statistically, large spectral widths occurred poleward of the red line emission, while small spectral widths occurred within or equatorward of the red line emission. Near simultaneous DMSP particle observations in the 20 eV to 20 keV range indicate that the poleward border of the red line emission and the gradient in spectral width occurred at the same latitude as the transition from auroral oval to polar rain particle energies. We conclude that the large spectral widths were not caused by particle precipitation associated with the auroral oval. There were two periods of special interest when the relationship between the red line and the spectral width broke down. The first of these happened during enhanced red line and green line (557.7 nm) emission, with a drop out of the radar scatter and an enhanced, narrow westward electrojet. We conclude that this event was a magnetospheric substorm occurring at much higher than usual latitudes. The second period of special interest happened when equatorward moving bands of large spectral width occurred within the region of scatter. Up to 4 of these bands were present during an interval of 100 minutes. Associated with these narrow bands of large spectral width were narrow channels of enhanced westward ion velocities. We conclude that these equatorward moving bands of large spectral width may be related to reconnection processes in the tail. The observations demonstrate that the tail continues to be active even under low solar wind energy input conditions. Furthermore, we conclude that the gradient in the spectral width may be used as a proxy for the polar cap boundary, but only with extreme caution.Key words. Ionosphere (ionosphere-magnetosphere inter-actions; polar ionosphere) – Magnetospheric physics (storms and substorms)

scholarly journals Factors determining spectral width of HF echoes from high latitudes

2007 ◽  
Vol 25 (3) ◽  
pp. 675-687 ◽  
Author(s):  
P. V. Ponomarenko ◽  
C. L. Waters ◽  
F. W. Menk
Keyword(s):  
Ionospheric Plasma ◽  
Spectral Width ◽  
Closed Field ◽  
Data Types ◽  
Standard Data ◽  
F Region ◽  
Radar Network ◽  
Scale Size ◽  
Radar Echo ◽  
Closed Field Line

Abstract. Spectral width is one of the standard data types produced by the Super Dual Auroral Radar Network (SuperDARN). A pronounced latitudinal gradient in spectral width has been reported in the literature and is used as an empirical proxy for the ionospheric footprint of the open-closed field-line boundary. In this work we investigated the daytime radar echo properties near the spectral width boundary using a multi-frequency sounding regime. We have found that the relatively large spectral width values ≥150 m/s observed poleward of the boundary are produced by ionospheric irregularities with lifetime τl≃10–25 ms, which is essentially independent of the scale size. These irregularities are statistically co-located with low-energy (~100 eV) electron precipitation, which may play a major role in producing F-region turbulence above 75 MLAT via restructuring the ionospheric plasma on time scales ~τl.

scholarly journals Rankin Inlet PolarDARN radar observations of duskward moving Sun-aligned optical forms

2008 ◽  
Vol 26 (9) ◽  
pp. 2711-2723 ◽  
Author(s):  
A. Koustov ◽  
K. Hosokawa ◽  
N. Nishitani ◽  
T. Ogawa ◽  
K. Shiokawa
Keyword(s):  
Large Scale ◽  
Temporal Variations ◽  
Global Scale ◽  
Hf Radar ◽  
Convection Pattern ◽  
Polar Cap ◽  
Signal Parameters ◽  
Velocity Reversal ◽  
Magnetic Perturbations ◽  
Resolute Bay

Abstract. On 15 February 2007, several duskward moving sun-aligned (SA) auroral forms have been observed by the all-sky camera at Resolute Bay, Nunavut (Canada). Concurrent observations with the Rankin Inlet (RANK) PolarDARN HF radar within the field-of-view of the camera showed signatures of moving auroral forms in all signal parameters with the most remarkable effects being the echo power drop and velocity reversal as the arc reached a specific radar beam/gate. Spatial and temporal variations of the velocity in the vicinity of the SA form are investigated. It is shown that the form-associated convection reversal was located poleward (duskward) of the global-scale convection reversal associated with the dawn cell of the large-scale convection pattern. Thus, the RANK radar was monitoring the polar cap portion of the global-scale convection pattern and its transition from the IMF By<0 to the By>0 situation. Magnetic perturbations associated with the SA form passing the zenith of several magnetometers are investigated. It is shown that although magnetometer signatures of the moving form were clear, the convection pattern derivation from magnetometer records alone is not straightforward.

scholarly journals On the occurrence and motion of decametre-scale irregularities in the sub-auroral, auroral, and polar cap ionosphere

2003 ◽  
Vol 21 (8) ◽  
pp. 1847-1868 ◽  
Author(s):  
M. L. Parkinson ◽  
J. C. Devlin ◽  
H. Ye ◽  
C. L. Waters ◽  
P. L. Dyson ◽  
...  
Keyword(s):  
Electric Fields ◽  
Spectral Width ◽  
Auroral Oval ◽  
Auroral Zone ◽  
Ionospheric Irregularities ◽  
Lower Latitude ◽  
Doppler Velocity ◽  
Auroral Ionosphere ◽  
Polar Cap ◽  
Sunspot Maximum

Abstract. The statistical occurrence of decametre-scale ionospheric irregularities, average line-of-sight (LOS) Doppler velocity, and Doppler spectral width in the sub-auroral, auroral, and polar cap ionosphere ( - 57°L to - 88°L) has been investigated using echoes recorded with the Tasman International Geospace Environment Radar (TIGER), a SuperDARN radar located on Bruny Island, Tasmania (147.2° E, 43.4° S geographic; - 54.6 °L). Results are shown for routine soundings made on the magnetic meridian beam 4 and the near zonal beam 15 during the sunspot maximum interval December 1999 to November 2000. Most echoes were observed in the nightside ionosphere, typically via 1.5-hop propagation near dusk and then via 0.5-hop propagation during pre-midnight to dawn. Peak occurrence rates on beam 4 were often > 60% near magnetic midnight and ~ - 70 °L. They increased and shifted equatorward and toward pre-midnight with increasing Kp (i.e. Bz southward). The occurrence rates remained very high for Kp > 4, de-spite enhanced D-region absorption due to particle precipitation. Average occurrence rates on beam 4 exhibited a relatively weak seasonal variation, consistent with known longitudinal variations in auroral zone magnetic activity (Basu, 1975). The average echo power was greatest between 23 and 07 MLT. Two populations of echoes were identified on both beams, those with low spectral width and a mode value of ~ 9 ms-1 (bin size of 2 ms-1) concentrated in the auroral and sub-auroral ionosphere (population A), and those with high spectral width and a mode value of ~ 70 ms-1 concentrated in the polar cap ionosphere (population B). The occurrence of population A echoes maximised post-midnight because of TIGER’s lower latitude, but the subset of the population A echoes observed near dusk had characteristics reminiscent of "dusk scatter" (Ruohoniemi et al., 1988). There was a dusk "bite out" of large spectral widths between ~ 15 and 21 MLT and poleward of - 67 °L, and a pre-dawn enhancement of large spectral widths between ~  03 and 07 MLT, centred on ~ - 61 °L. The average LOS Doppler velocities revealed that frequent westward jets of plasma flow occurred equatorward of, but overlapping, the diffuse auroral oval in the pre-midnight sector.Key words. Ionosphere (auroral ionosphere; electric fields and currents, ionospheric irregularities)

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