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>

scholarly journals Electron heating by HF pumping of high-latitude ionospheric F-region plasma near magnetic zenith

2020 ◽  
Vol 38 (2) ◽  
pp. 297-307 ◽  
Author(s):  
Thomas B. Leyser ◽  
Björn Gustavsson ◽  
Theresa Rexer ◽  
Michael T. Rietveld
Keyword(s):  
Electron Temperature ◽  
Pump Beam ◽  
Electron Heating ◽  
Incoherent Scatter ◽  
F Region ◽  
Left Handed ◽  
Parameter Values ◽  
Uhf Radar ◽  
Region Plasma ◽  
Magnetic Zenith

Abstract. High-frequency electromagnetic pumping of ionospheric F-region plasma at high and mid latitudes gives the strongest plasma response in magnetic zenith, antiparallel to the geomagnetic field in the Northern Hemisphere. This has been observed in optical emissions from the pumped plasma turbulence, electron temperature enhancements, filamentary magnetic field-aligned plasma density irregularities, and in self-focusing of the pump beam in magnetic zenith. We present results of EISCAT (European Incoherent SCATter association) Heating-induced magnetic-zenith effects observed with the EISCAT UHF incoherent scatter radar. With heating transmitting a left-handed circularly polarized pump beam towards magnetic zenith, the UHF radar was scanned in elevation in steps of 1.0 and 1.5∘ around magnetic zenith. The electron energy equation was integrated to model the electron temperature and associated electron heating rate and optimized to fit the plasma parameter values measured with the radar. The experimental and modelling results are consistent with pump wave propagation in the L mode in magnetic zenith, rather than in the O mode.

scholarly journals Plasma flows, Birkeland currents and auroral forms in relation to the Svalgaard-Mansurov effect

2012 ◽  
Vol 30 (5) ◽  
pp. 817-830 ◽  
Author(s):  
P. E. Sandholt ◽  
C. J. Farrugia
Keyword(s):  
Magnetic Field ◽  
Open Field ◽  
Central Element ◽  
Flow Channel ◽  
Plasma Convection ◽  
Polar Cap ◽  
Flow Channels ◽  
Field Lines ◽  
Current Systems ◽  
Birkeland Currents

Abstract. The traditional explanation of the polar cap magnetic deflections, referred to as the Svalgaard-Mansurov effect, is in terms of currents associated with ionospheric flow resulting from the release of magnetic tension on newly open magnetic field lines. In this study, we aim at an updated description of the sources of the Svalgaard-Mansurov effect based on recent observations of configurations of plasma flow channels, Birkeland current systems and aurorae in the magnetosphere-ionosphere system. Central to our description is the distinction between two different flow channels (FC 1 and FC 2) corresponding to two consecutive stages in the evolution of open field lines in Dungey cell convection, with FC 1 on newly open, and FC 2 on old open, field lines. Flow channel FC 1 is the result of ionospheric Pedersen current closure of Birkeland currents flowing along newly open field lines. During intervals of nonzero interplanetary magnetic field By component FC 1 is observed on either side of noon and it is accompanied by poleward moving auroral forms (PMAFs/prenoon and PMAFs/postnoon). In such cases the next convection stage, in the form of flow channel FC 2 on the periphery of the polar cap, is particularly important for establishing an IMF By-related convection asymmetry along the dawn-dusk meridian, which is a central element causing the Svalgaard-Mansurov effect. FC 2 flows are excited by the ionospheric Pedersen current closure of the northernmost pair of Birkeland currents in the four-sheet current system, which is coupled to the tail magnetopause and flank low-latitude boundary layer. This study is based on a review of recent statistical and event studies of central parameters relating to the magnetosphere-ionosphere current systems mentioned above. Temporal-spatial structure in the current systems is obtained by ground-satellite conjunction studies. On this point we emphasize the important information derived from the continuous ground monitoring of the dynamical behaviour of aurora and plasma convection during intervals of well-organised solar wind plasma and magnetic field conditions in interplanetary coronal mass ejections (ICMEs) during their Earth passage.

scholarly journals Orientation of the cross-field anisotropy of small-scale ionospheric irregularities and direction of plasma convection

2005 ◽  
Vol 23 (4) ◽  
pp. 1227-1237 ◽  
Author(s):  
E. D. Tereshchenko ◽  
N. Yu. Romanova ◽  
A. V. Koustov
Keyword(s):  
Auroral Zone ◽  
Small Scale ◽  
Plasma Convection ◽  
Polar Cap ◽  
F Region ◽  
Radio Signals ◽  
The Cross ◽  
Satellite Radar ◽  
Convection Patterns ◽  
The Relationship

Abstract. The relationship between the orientation of the small-scale ionospheric irregularity anisotropy in a plane perpendicular to the geomagnetic field and the direction of plasma convection in the F region is investigated. The cross-field anisotropy of irregularities is obtained by fitting theoretical expectations for the amplitude scintillations of satellite radio signals to the actual measurements. Information on plasma convection was provided by the SuperDARN HF radars. Joint satellite/radar observations in both the auroral zone and the polar cap are considered. It is shown that the irregularity cross-field anisotropy agrees quite well with the direction of plasma convection with the best agreement for events with quasi-stationary convection patterns.

Higher-order electron modes in a two-electron-temperature plasma

1990 ◽  
Vol 43 (2) ◽  
pp. 239-255 ◽  
Author(s):  
R. L. Mace ◽  
M. A. Hellberg
Keyword(s):  
Electron Temperature ◽  
Higher Order ◽  
Hot Electron ◽  
Temperature Plasma ◽  
Critical Curves ◽  
Higher Order Modes ◽  
Electron Acoustic Wave ◽  
Electron Acoustic ◽  
Relationship Of ◽  
The Relationship

We discuss critical curves that allow us to predict, qualitatively, the topological behaviour of higher-order modes in a two-electron-temperature plasma as wavenumber and hot electron fraction are varied. The relationship of these higher-order modes to the electron-acoustic wave is elucidated.

scholarly journals Daytime ionospheric absorption features in the polar cap associated with poleward drifting F-region plasma patches

1998 ◽  
Vol 50 (2) ◽  
pp. 107-117 ◽  
Author(s):  
Masanori Nishino ◽  
Satonori Nozawa ◽  
Jan A. Holtet
Keyword(s):  
Polar Cap ◽  
F Region ◽  
Ionospheric Absorption ◽  
Absorption Features ◽  
Region Plasma

scholarly journals Polar cap flow channel events: spontaneous and driven responses

2010 ◽  
Vol 28 (11) ◽  
pp. 2015-2025 ◽  
Author(s):  
P. E. Sandholt ◽  
Y. Andalsvik ◽  
C. J. Farrugia
Keyword(s):  
Magnetic Field ◽  
Case Studies ◽  
Flow Channel ◽  
Polar Cap ◽  
Specific Flow ◽  
Temporal Behaviour ◽  
Magnetic Signature ◽  
Ground Magnetic ◽  
The Relationship ◽  
Birkeland Currents

Abstract. We present two case studies of specific flow channel events appearing at the dusk and/or dawn polar cap boundary during passage at Earth of interplanetary (IP) coronal mass ejections (ICMEs) on 10 January and 25 July 2004. The channels of enhanced (>1 km/s) antisunward convection are documented by SuperDARN radars and dawn-dusk crossings of the polar cap by the DMSP F13 satellite. The relationship with Birkeland currents (C1–C2) located poleward of the traditional R1–R2 currents is demonstrated. The convection events are manifest in ground magnetic deflections obtained from the IMAGE (International Monitor for Auroral Geomagnetic Effects) Svalbard chain of ground magnetometer stations located within 71–76° MLAT. By combining the ionospheric convection data and the ground magnetograms we are able to study the temporal behaviour of the convection events. In the two ICME case studies the convection events belong to two different categories, i.e., directly driven and spontaneous events. In the 10 January case two sharp southward turnings of the ICME magnetic field excited corresponding convection events as detected by IMAGE and SuperDARN. We use this case to determine the ground magnetic signature of enhanced flow channel events (the NH-dusk/By<0 variant). In the 25 July case a several-hour-long interval of steady southwest ICME field (Bz<0; By<0) gave rise to a long series of spontaneous convection events as detected by IMAGE when the ground stations swept through the 12:00–18:00 MLT sector. From the ground-satellite conjunction on 25 July we infer the pulsed nature of the polar cap ionospheric flow channel events in this case. The typical duration of these convection enhancements in the polar cap is 10 min.

scholarly journals Plasma flow channels at the dawn/dusk polar cap boundaries: momentum transfer on old open field lines and the roles of IMF <I>B<sub>y</sub></I> and conductivity gradients

2009 ◽  
Vol 27 (4) ◽  
pp. 1527-1554 ◽  
Author(s):  
P. E. Sandholt ◽  
C. J. Farrugia
Keyword(s):  
Solar Wind ◽  
Momentum Transfer ◽  
Open Field ◽  
Flow Channel ◽  
Polar Cap ◽  
Ionospheric Conductivity ◽  
Flow Channels ◽  
Precipitation Regimes ◽  
Polar Rain ◽  
Field Lines

Abstract. Using DMSP F13 data in conjunction with IMF data we investigate the newly discovered channels of enhanced (1.5–3 km/s) antisunward convection occurring at the dawn (06:00–09:00 MLT) or dusk (15:00–18:00 MLT) flanks of the polar cap for different combinations of IMF By polarity, hemisphere (NH/SH) and the dawn/dusk MLTs. Dawn-side cases where this flow channel appears occur for the following combinations: NH-dawn/By>0 and SH-dawn/By<0. The dusk-side cases are: NH-dusk/By<0 and SH-dusk/By>0. The flow channels are placed in the context of particle precipitation regimes/boundaries and ionospheric conductivity gradients. They are found to be threaded by "old open field lines" ("time since reconnection" >10 min) characterized by polar rain precipitation. In the dawn-side cases (NH-dawn/By>0 and SH-dawn/By<0) and in a Parker spiral field, the polar rain contains the "solar wind strahl" component. The convection enhancement is attributed to the Pedersen current closure of Birkeland current sheets (C1 and C2) in the polar cap (C1) and at the polar cap boundary (C2). The low ionospheric conductivity in the polar cap, particularly in the winter hemisphere, is compensated by an enhanced electric field driving the flow channel there. This is momentum transfer from the solar wind via dynamo action taking place in the combined current system of the high- and low-latitude boundary layers (HBL/LLBL). The conductivity gradient at the polar cap boundary contributes to establishing the convection channel and the associated enhancement of the dawn-dusk convection asymmetry extending beyond the dawn-dusk terminator during intervals of nonzero IMF By component. The HBL/LLBL-ionosphere coupling via Birkeland currents C1/C2 is a source of dawn-dusk convection asymmetry and Svalgaard-Mansurov effect which must be added to the effect of magnetic tension acting on "newly open field lines".

scholarly journals Two-Dimensional Structure of Flow Channels and Associated Upward Field-Aligned Currents: Model and Observations

2021 ◽  
Vol 8 ◽  
Author(s):  
Larry. R. Lyons ◽  
Yukitoshi Nishimura ◽  
Chih-Ping Wang ◽  
Jiang Liu ◽  
William. A. Bristow
Keyword(s):  
Plasma Sheet ◽  
Auroral Oval ◽  
Flow Channel ◽  
Dimensional Structure ◽  
Convection Cell ◽  
Two Dimensional ◽  
Flow Channels ◽  
Structure Of Flow ◽  
Low Entropy ◽  
Flow Burst

Flow bursts are a major component of transport within the plasma sheet and auroral oval (where they are referred to as flow channels), and lead to a variety of geomagnetic disturbances as they approach the inner plasma sheet (equatorward portion of the auroral oval). However, their two-dimensional structure as they approach the inner plasma sheet has received only limited attention. We have examined this structure using both the Rice Convection Model (RCM) and ground-based radar and all sky imager observations. As a result of the energy dependent magnetic drift, the low entropy plasma of a flow burst spreads azimuthally within the inner plasma sheet yielding specific predictions of subauroral polarization stream (SAPS) and dawnside auroral polarization stream (DAPS) enhancements that are related to the field-aligned currents associated with the flow channel. Flow channels approximately centered between the dawn and dusk large-scale convection cells are predicted to give significant enhancements of both SAPS and DAPS, whereas flow channel further toward the dusk (dawn) convection cell show a far more significant enhancement of SAPS (DAPS) than for DAPS (SAPS). We present observations for cases having good coverage of flow channels as they approach the equatorward portion of the auroral oval and find very good qualitative agreement with the above RCM predictions, including the predicted differences with respect to flow burst location. Despite there being an infinite variety of flow channels’ plasma parameters and of background plasma sheet and auroral oval conditions, the observations show the general trends predicted by the RCM simulations with the idealized parameters. This supports that RCM predictions of the azimuthal spread of a low-entropy plasma sheet plasma and its associated FAC and flow responses give a realistic physical description of the structure of plasma sheet flow bursts (auroral oval flow channels) as they reach the inner plasma sheet (near the equatorward edge of the auroral oval).

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 Electron heating by HF-pumping of high-latitude ionospheric F-region plasma near magnetic zenith

2019 ◽  
Author(s):  
Thomas B. Leyser ◽  
Björn Gustavsson ◽  
Theresa Rexer ◽  
Michael T. Rietveld
Keyword(s):  
Electron Temperature ◽  
Pump Beam ◽  
Electron Heating ◽  
Incoherent Scatter ◽  
F Region ◽  
Left Handed ◽  
Parameter Values ◽  
Uhf Radar ◽  
Region Plasma ◽  
Magnetic Zenith

Abstract. High frequency electromagnetic pumping of ionospheric F-region plasma at high and mid latitudes gives the strongest plasma response in magnetic zenith, antiparallel to the geomagnetic field in the northern hemisphere. This has been observed in optical emissions from the pumped plasma turbulence, electron temperature enhancements, filamentary magnetic field-aligned plasma density irregularities, and in self-focusing of the pump beam in magnetic zenith. We present results of EISCAT (European Incoherent SCATter association) Heating-induced magnetic-zenith effects observed with the EISCAT UHF incoherent scatter radar. With Heating transmitting a left-handed circularly polarised pump beam towards magnetic zenith, the UHF radar was scanned in elevation in steps of 1.0° and 1.5° around magnetic zenith. The electron energy equation was integrated to model the electron temperature and associated electron heating rate and optimized to fit the plasma parameter values measured with the radar. The experimental and modeling results are consistent with pump wave propagation in the L mode in magnetic zenith, rather than in the O mode.

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