scholarly journals THEMIS ground-space observations during the development of auroral spirals

2009 ◽  
Vol 27 (11) ◽  
pp. 4317-4332 ◽  
Author(s):  
A. Keiling ◽  
V. Angelopoulos ◽  
J. M. Weygand ◽  
O. Amm ◽  
E. Spanswick ◽  
...  
Keyword(s):  
Plasma Flow ◽  
Simultaneous Observation ◽  
Model Calculations ◽  
Expansion Phase ◽  
Geocentric Distance ◽  
Field Aligned Current ◽  
Auroral Arcs ◽  
Downward Currents ◽  
A Current ◽  
Space Observations

Abstract. A simultaneous observation of an auroral spiral and its generator region in the near-Earth plasma sheet is rather unlikely. Here we present such observations using the THEMIS spacecraft as well as the THEMIS ground network of all-sky imagers and magnetometers. Two consecutive auroral spirals separated by approximately 14 min occurred during a substorm on 19 February 2008. The spirals formed during the expansion phase and a subsequent intensification, and were among the brightest features in the aurora with diameters of 200–300 km. The duration for the formation and decay of each spiral was less than 60 s. Both spirals occurred shortly after the formation of two oppositely rotating plasma flow vortices in space, which were also accompanied by dipolarizations and ion injections, at ~11 RE geocentric distance. Observations and model calculations also give evidence for a magnetic-field-aligned current generation of approximately 0.1 MA via the flow vortices, connecting the generator region of the spirals with the ionosphere, during the formation of both spirals. In the ionosphere, a pair of equivalent ionospheric current (EIC) vortices with opposite rotations (corresponding to upward and downward currents) was present during both auroral spirals with enhanced EICs and ionospheric flows at the locations of the auroral spirals and along the auroral arcs. The combined ground and space observations suggest that each auroral spiral was powered by two oppositely rotating plasma flow vortices that caused a current enhancement in the substorm current wedge.

Transient cusp ionospheric disturbances caused by a solar wind dynamic pressure enhancement

2021 ◽  
Author(s):  
Jianjun Liu
Keyword(s):  
Plasma Flow ◽  
Dynamic Pressure ◽  
Geomagnetic Disturbance ◽  
Flow Reversal ◽  
Drift Motion ◽  
Zhongshan Station ◽  
Shock Impingement ◽  
Field Aligned Current ◽  
Convection Patterns ◽  
The Antarctic

<p>Interplanetary (IP) shock driven sudden compression produces disturbances in the polar ionosphere. Various studies have investigated the effects of IP shock using imagers and radars. However, very few studies have reported the plasma flow reversal and a sudden vertical plasma drift motion following a CME driven IP shock. We report on the cusp ionospheric features following an IP shock impingement on 16 June 2012, using SuperDARN radar and digisonde from the Antarctic Zhongshan Station (ZHO). SuperDARN ZHO radar observed instant strong plasma flow reversal during the IP shock driven sudden impulse (SI) with a suppression in the number of backscatter echoes. Besides, we also report on a “Doppler Impulse” phenomenon, an instant and brief downward plasma motion, were observed by the digisonde in response to the SI and discuss the possible physical causes. Geomagnetic disturbance and convection patterns indicate the flow reversal was generated by the downward field-aligned current (FAC). We speculate that sudden enhancement in ionization associated with SI is responsible for generating the Doppler Impulse phenomenon.</p>

scholarly journals Ionospheric signatures during a magnetospheric flux rope event

2008 ◽  
Vol 26 (12) ◽  
pp. 3967-3977 ◽  
Author(s):  
L. Juusola ◽  
O. Amm ◽  
H. U. Frey ◽  
K. Kauristie ◽  
R. Nakamura ◽  
...  
Keyword(s):  
Flux Rope ◽  
Recovery Phase ◽  
Expansion Phase ◽  
Northern Fennoscandia ◽  
Ionospheric Region ◽  
Image Satellite ◽  
Imaging Camera ◽  
Flux Ropes ◽  
Field Aligned Current ◽  
Upward Current

Abstract. On 13 August 2002, during a substorm, Cluster encountered two earthward moving flux ropes (FR) in the central magnetotail. The first FR was observed during the expansion phase of the substorm, and the second FR during the recovery phase. In the conjugate ionospheric region in Northern Fennoscandia, the ionospheric equivalent currents were observed by the MIRACLE network and the auroral evolution was monitored by the Wideband Imaging Camera (WIC) on-board the IMAGE satellite. Extending the study of Amm et al. (2006), we examine and compare the possible ionospheric signatures associated with the two FRs. Amm et al. studied the first event in detail and found that the ionospheric footprint of Cluster coincided with a region of downward field-aligned current. They suggested that this region of downward current, together with a trailing region of upward current further southwestward, might correspond to the ends of the FR. Unlike during the first FR, however, we do not see any clear ionospheric features associated with the second one. In the GSM xy-plane, the first flux rope axis was tilted with respect to the y-direction by 29°, while the second flux rope axis was almost aligned in the y-direction, with an angle of 4° only. It is possible that due to the length and orientation of the second FR, any ionospheric signatures were simply mapped outside the region covered by the ground-based instruments. We suggest that the ground signatures of a FR depend on the orientation and the length of the structure.

scholarly journals Plasma transport along discrete auroral arcs and its contribution to the ionospheric plasma convection

2008 ◽  
Vol 26 (11) ◽  
pp. 3279-3293 ◽  
Author(s):  
A. Kullen ◽  
S. Buchert ◽  
T. Karlsson ◽  
T. Johansson ◽  
S. Lileo ◽  
...  
Keyword(s):  
Plasma Flow ◽  
Strong Dependence ◽  
Background Plasma ◽  
Plasma Transport ◽  
Plasma Convection ◽  
Plasma Flows ◽  
Maximum Phase ◽  
Field Peak ◽  
Auroral Arcs

Abstract. The role of intense high-altitude electric field (E-field) peaks for large-scale plasma convection is investigated with the help of Cluster E-field, B-field and density data. The study covers 32 E-field events between 4 and 7 RE geocentric distance, with E-field magnitudes in the range 500–1000 mV/m when mapped to ionospheric altitude. We focus on E-field structures above the ionosphere that are typically coupled to discrete auroral arcs and their return current region. Connected to such E-field peaks are rapid plasma flows directed along the discrete arcs in opposite directions on each side of the arc. Nearly all the E-field events occur during active times. A strong dependence on different substorm phases is found: a majority of intense E-field events appearing during substorm expansion or maximum phase are located on the nightside oval, while most recovery events occur on the dusk-to-dayside part of the oval. For most expansion and maximum phase cases, the average background plasma flow is in the sunward direction. For a majority of recovery events, the flow is in the anti-sunward direction. The net plasma flux connected to a strong E-field peak is in two thirds of the cases in the same direction as the background plasma flow. However, in only one third of the cases the strong flux caused by an E-field peak makes an important contribution to the plasma transport within the boundary plasma sheet. For a majority of events, the area covered by rapid plasma flows above discrete arcs is too small to have an effect on the global convection. This questions the role of discrete auroral arcs as major driver of plasma convection.

Two‐Dimensional Maps of In Situ Ionospheric Plasma Flow Data Near Auroral Arcs Using Auroral Imagery

2019 ◽  
Author(s):  
Robert Clayton ◽  
Kristina Lynch ◽  
Matt Zettergren ◽  
Meghan Burleigh ◽  
Mark Conde ◽  
...  
Keyword(s):  
Plasma Flow ◽  
Ionospheric Plasma ◽  
Two Dimensional ◽  
Flow Data ◽  
Auroral Arcs

scholarly journals Irregular HF radio propagation on a subauroral path during magnetospheric substorms

2006 ◽  
Vol 24 (7) ◽  
pp. 1839-1849 ◽  
Author(s):  
D. V. Blagoveshchensky ◽  
T. D. Borisova ◽  
J. W. MacDougall
Keyword(s):  
Signal Amplitude ◽  
Radio Propagation ◽  
Propagation Path ◽  
Magnetospheric Substorms ◽  
Model Calculations ◽  
Expansion Phase ◽  
Modeling Process ◽  
Main Ionospheric Trough ◽  
Ionospheric Gradients ◽  
The Impact

Abstract. The impact of the main ionospheric trough, sporadic structures, gradients and inhomogeneities of the subpolar ionosphere during substorms on the signal amplitude, azimuthal angles of arrival, and propagation modes for the radio path Ottawa (Canada)-St. Petersburg (Russia) was considered. This subauroral path with the length of about 6600 km has approximately an east-west orientation. The main goals are to carry out numerical modeling of radio propagation for the path and to compare the model calculations with experimental results. Wave absorption and effects of focusing and divergence of rays were taken into consideration in the radio wave modeling process. The following basic results were obtained: The signal amplitude increases by 20–30 dB 1–1.5 h before the substorm expansion phase onset. At the same time the signal azimuth deviates towards north of the great circle arc for the propagation path. Compared with quiet periods there are effects due to irregularities and gradients in the area of the polar edge of the main ionospheric trough on the passing signals. Propagation mechanisms also change during substorms. The growth of signal amplitude before the substorm can be physically explained by both a decrease of the F2-layer ionization and a growth of the F2-layer height that leads to a decrease of the signal field divergence and to a drop of the collision frequency. Ionospheric gradients are also important. This increase of signal level prior to a substorm could be used for forecasting of space weather disturbed conditions.

scholarly journals An auroral westward flow channel (AWFC) and its relationship to field-aligned current, ring current, and plasmapause location determined using multiple spacecraft observations

2007 ◽  
Vol 25 (1) ◽  
pp. 59-76 ◽  
Author(s):  
M. L. Parkinson ◽  
J. A. Wild ◽  
C. L. Waters ◽  
M. Lester ◽  
E. A. Lucek ◽  
...  
Keyword(s):  
Plasma Sheet ◽  
Large Scale ◽  
Ring Current ◽  
Narrow Channel ◽  
Recovery Phase ◽  
Global Scale ◽  
Auroral Oval ◽  
Flow Channel ◽  
Expansion Phase ◽  
Field Aligned Current

Abstract. An auroral westward flow channel (AWFC) is a latitudinally narrow channel of unstable F-region plasma with intense westward drift in the dusk-to-midnight sector ionosphere. AWFCs tend to overlap the equatorward edge of the auroral oval, and their life cycle is often synchronised to that of substorms: they commence close to substorm expansion phase onset, intensify during the expansion phase, and then decay during the recovery phase. Here we define for the first time the relationship between an AWFC, large-scale field-aligned current (FAC), the ring current, and plasmapause location. The Tasman International Geospace Environment Radar (TIGER), a Southern Hemisphere HF SuperDARN radar, observed a jet-like AWFC during ~08:35 to 13:28 UT on 7 April 2001. The initiation of the AWFC was preceded by a band of equatorward expanding ionospheric scatter (BEES) which conveyed an intense poleward electric field through the inner plasma sheet. Unlike previous AWFCs, this event was not associated with a distinct substorm surge; rather it occurred during an interval of persistent, moderate magnetic activity characterised by AL~−200 nT. The four Cluster spacecraft had perigees within the dusk sector plasmasphere, and their trajectories were magnetically conjugate to the radar observations. The Waves of High frequency and Sounder for Probing Electron density by Relaxation (WHISPER) instruments on board Cluster were used to identify the plasmapause location. The Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) EUV experiment also provided global-scale observations of the plasmapause. The Cluster fluxgate magnetometers (FGM) provided successive measurements specifying the relative location of the ring current and filamentary plasma sheet current. An analysis of Iridium spacecraft magnetometer measurements provided estimates of large-scale ionospheric FAC in relation to the AWFC evolution. Peak flows in the AWFC were located close to the peak of a Region 2 downward FAC, located just poleward of the plasmapause. DMSP satellite observations confirmed the AWFC was located equatorward of the nightside plasmasheet, sometimes associated with ~10 keV ion precipitation.

scholarly journals A physical explanation for the magnetic decrease ahead of dipolarization fronts

2015 ◽  
Vol 33 (10) ◽  
pp. 1301-1309 ◽  
Author(s):  
Z. H. Yao ◽  
J. Liu ◽  
C. J. Owen ◽  
C. Forsyth ◽  
I. J. Rae ◽  
...  
Keyword(s):  
Plasma Pressure ◽  
Current Loop ◽  
Tail Current ◽  
Dipolarization Front ◽  
Local Current ◽  
Order Of Magnitude ◽  
Closed Current ◽  
Field Aligned Current ◽  
The Cross ◽  
A Current

Abstract. Recent studies have shown that the ambient plasma in the near-Earth magnetotail can be compressed by the arrival of a dipolarization front (DF). In this paper we study the variations in the characteristics of currents flowing in this compressed region ahead of the DF, particularly the changes in the cross-tail current, using observations from the THEMIS satellites. Since we do not know whether the changes in the cross-tail current lead to a field-aligned current formation or just form a current loop in the magnetosphere, we thus use redistribution to represent these changes of local current density. We found that (1) the redistribution of the cross-tail current is a common feature preceding DFs; (2) the redistribution of cross-tail current is caused by plasma pressure gradient ahead of the DF and (3) the resultant net current redistributed by a DF is an order of magnitude smaller than the typical total current associated with a moderate substorm current wedge (SCW). Moreover, our results also suggest that the redistributed current ahead of the DF is closed by currents on the DF itself, forming a closed current loop around peaks in plasma pressure, what is traditionally referred to as a banana current.

scholarly journals Features of auroral breakup obtained using data of ground-based television observations: case study

2009 ◽  
Vol 27 (4) ◽  
pp. 1413-1422 ◽  
Author(s):  
E. E. Antonova ◽  
I. A. Kornilov ◽  
T. A. Kornilova ◽  
O. I. Kornilov ◽  
M. V. Stepanova
Keyword(s):  
Imaging Technique ◽  
Magnetic Disturbance ◽  
Magnetic Fluctuations ◽  
Relative Timing ◽  
Expansion Phase ◽  
Auroral Breakup ◽  
Image Filtration ◽  
Using Data ◽  
Auroral Arcs

Abstract. The knowledge about the relative timing of events during the substorm expansion phase onset is very important for understanding the physics of substorms. In this work ground-based television (TV) imaging technique was used for observations of the first auroral arc brightening near zenith of TV chamber for the case of an isolated substorm. The method of the TV image filtration was used giving the possibility to analyze motion of sub visual auroral arcs. The analysis of the connection between the first auroral arc brightening and the beginning of magnetic disturbance was carried out. It was shown that luminosity disturbance is absent to the pole of breakup arc before the breakup and there exist a delay time between the brightening and start of intense magnetic fluctuations in the Pi1–Pi2 frequency ranges. The results obtained have been compared with predictions of theories of auroral breakup.

Sign in / Sign up

Export Citation Format

Share Document