scholarly journals Electron density depletion region observed in the polar cap ionosphere

2020 ◽  
Author(s):  
L. M. Bjoland ◽  
Y. Ogawa ◽  
U. P. Løvhaug ◽  
D. A. Lorentzen ◽  
S. M. Hatch ◽  
...  
Keyword(s):  
Electron Density ◽  
Depletion Region ◽  
Polar Cap ◽  
Density Depletion

scholarly journals Polar patches observed by ESR and their possible origin in the cusp region

2000 ◽  
Vol 18 (9) ◽  
pp. 1043-1053 ◽  
Author(s):  
A. M. Smith ◽  
S. E. Pryse ◽  
L. Kersley
Keyword(s):  
Energy Distribution ◽  
Electron Density ◽  
Plasma Flow ◽  
Plasma Temperature ◽  
Soft Particle ◽  
Polar Ionosphere ◽  
Polar Cap ◽  
Particle Precipitation ◽  
Cusp Region ◽  
Reconnection Site

Abstract. Observations by the EISCAT Svalbard radar in summer have revealed electron density enhancements in the magnetic noon sector under conditions of IMF Bz southward. The features were identified as possible candidates for polar-cap patches drifting anti-Sunward with the plasma flow. Supporting measurements by the EISCAT mainland radar, the CUTLASS radar and DMSP satellites, in a multi-instrument study, suggested that the origin of the structures lay upstream at lower latitudes, with the modulation in density being attributed to variability in soft-particle precipitation in the cusp region. It is proposed that the variations in precipitation may be linked to changes in the location of the reconnection site at the magnetopause, which in turn results in changes in the energy distribution of the precipitating particles.Key words: Ionosphere (ionosphere-magnetosphere interactions; plasma temperature and density; polar ionosphere)

Break up of a polar cap patch in the nightside ionosphere due to a flow channel event

2020 ◽  
Author(s):  
Elizabeth Donegan-Lawley ◽  
Alan Wood ◽  
Gareth Dorrian ◽  
Alexandra Fogg ◽  
Timothy Yeoman ◽  
...  
Keyword(s):  
Electron Density ◽  
Global Navigation Satellite System ◽  
Satellite System ◽  
Flow Channel ◽  
Navigation Satellite ◽  
Polar Cap ◽  
Incoherent Scatter ◽  
Radar Network ◽  
Incoherent Scatter Radars ◽  
Global Navigation Satellite

<p>Flow channel events have previously been observed breaking up polar cap patches on the dayside ionosphere but, to the best of our knowledge, have not been observed on the nightside. We report observations of a flow channel event in the evening of the 9th January 2019 under quiet geomagnetic conditions. This multi-instrument study was undertaken using a combination of multiple EISCAT (European Incoherent Scatter) radars, SuperDARN (Super Dual Auroral Radar Network), MSP (Meridian Scanning Photometer) and GNSS (Global Navigation Satellite System) scintillation data. These data were used to build a picture of the evening’s observations from 1800 to 2359 UT. The flow channel event lasted a total of 13 minutes and was responsible for segmenting a polar cap patch. A decrease in electron density was observed, from a patch value of 1.4x10<sup>11</sup> m<sup>3</sup> to a minimum value of 5x10<sup>10</sup> m<sup>3</sup>. In addition, ion velocities in excess of 1000 ms<sup>-1</sup> and ion temperatures of greater than 2000 K were also observed. </p>

scholarly journals EISCAT observations of unusual flows in the morning sector associated with weak substorm activity

1994 ◽  
Vol 12 (6) ◽  
pp. 541-553 ◽  
Author(s):  
N. J. Fox ◽  
M. Lockwood ◽  
S. W. H. Cowley ◽  
M. P. Freeman ◽  
E. Friis-Christensen ◽  
...  
Keyword(s):  
Auroral Oval ◽  
Geosynchronous Orbit ◽  
Polar Cap ◽  
Expansion Phase ◽  
Geomagnetic Tail ◽  
Density Depletion ◽  
Significant Difference ◽  
Pi2 Pulsations ◽  
Substorm Activity ◽  
Open Flux

Abstract. A discussion is given of plasma flows in the dawn and nightside high-latitude ionospheric regions during substorms occurring on a contracted auroral oval, as observed using the EISCAT CP-4-A experiment. Supporting data from the PACE radar, Greenland magnetometer chain, SAMNET magnetometers and geostationary satellites are compared to the EISCAT observations. On 4 October 1989 a weak substorm with initial expansion phase onset signatures at 0030 UT, resulted in the convection reversal boundary observed by EISCAT (at ~0415 MLT) contracting rapidly poleward, causing a band of elevated ionospheric ion temperatures and a localised plasma density depletion. This polar cap contraction event is shown to be associated with various substorm signatures; Pi2 pulsations at mid-latitudes, magnetic bays in the midnight sector and particle injections at geosynchronous orbit. A similar event was observed on the following day around 0230 UT (~0515 MLT) with the unusual and significant difference that two convection reversals were observed, both contracting poleward. We show that this feature is not an ionospheric signature of two active reconnection neutral lines as predicted by the near-Earth neutral model before the plasmoid is "pinched off", and present two alternative explanations in terms of (1) viscous and lobe circulation cells and (2) polar cap contraction during northward IMF. The voltage associated with the anti-sunward flow between the reversals reaches a maximum of 13 kV during the substorm expansion phase. This suggests it to be associated with the polar cap contraction and caused by the reconnection of open flux in the geomagnetic tail which has mimicked "viscous-like" momentum transfer across the magnetopause.

Imaging riometer and HF radar measurements of driftingFregion electron density structures in the polar cap

1993 ◽  
Vol 98 (A5) ◽  
pp. 7757-7764 ◽  
Author(s):  
T. J. Rosenberg ◽  
Z. Wang ◽  
A. S. Rodger ◽  
J. R. Dudeney ◽  
K. B. Baker
Keyword(s):  
Electron Density ◽  
Hf Radar ◽  
Polar Cap ◽  
Radar Measurements
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