scholarly journals Plasma sheet fast flows and auroral dynamics during substorm: a case study

2002 ◽  
Vol 20 (3) ◽  
pp. 341-347 ◽  
Author(s):  
N. L. Borodkova ◽  
A. G. Yahnin ◽  
K. Liou ◽  
J.-A. Sauvaud ◽  
A. O. Fedorov ◽  
...  
Keyword(s):  
Plasma Sheet ◽  
Neutral Line ◽  
Filamentary Structure ◽  
Storms And Substorms ◽  
Flow Directions ◽  
Auroral Phenomena ◽  
Fast Flow ◽  
The Relationship ◽  
Earthward Flow

Abstract. Interball-1 observations of a substorm development in the mid-tail on 16 December 1998 are compared with the auroral dynamics obtained from the Polar UV imager. Using these data, the relationship between plasma flow directions in the tail and the location of the auroral activation is examined. Main attention is given to tailward and earth-ward plasma flows, interpreted as signatures of a Near Earth Neutral Line (NENL). It is unambiguously shown that in the mid-plasma sheet the flows were directed tailward when the auroral bulge developed equatorward of the spacecraft ionospheric footprint. On the contrary, when active auroras moved poleward of the Interball-1 projection, earthward fast flow bursts were observed. This confirms the concept that the NENL (or flow reversal region) is the source of auroras forming the poleward edge of the auroral bulge. The observed earthward flow bursts have all typical signatures of Bursty Bulk Flows (BBFs), described by Angelopolous et al. (1992). These BBFs are related to substorm activations starting at the poleward edge of the expanded auroral bulge. We interpret the BBFs as a result of reconnection pulses occurring tail-ward of Interball-1. In addition, some non-typically observed phenomena were detected in the plasma sheet during this substorm: (i) tailward/earthward flows were superimposed on a very strong duskward flow, and (ii) wavy structures of both magnetic field and plasma density were registered. The latter observation is probably linked to the filamentary structure of the current sheet.Key words. Magnetospheric physics (auroral phenomena; plasma sheet; storms and substorms)

scholarly journals Revisiting substorm events with preonset aurora

2018 ◽  
Vol 36 (5) ◽  
pp. 1419-1438 ◽  
Author(s):  
Yukinaga Miyashita ◽  
Akimasa Ieda
Keyword(s):  
Neutral Line ◽  
Timing Analysis ◽  
Future Studies ◽  
Open Questions ◽  
Storms And Substorms ◽  
Auroral Phenomena ◽  
Earthward Flow ◽  
Arrival Timing ◽  
Poleward Expansion

Abstract. Nishimura et al. (2010) proposed a new plasma intrusion or preonset aurora scenario of substorm triggering. In this scenario, a substorm is triggered by a fast earthward flow generated at the distant neutral line which corresponds to a preonset auroral streamer or arc in the ionosphere propagating from the auroral poleward boundary to the initial auroral brightening site, i.e., “preonset aurora”. In the present paper, we revisited three substorm events reported as being triggered by such a mechanism related to preonset auroras, based on THEMIS ground-based all-sky imager data. Unlike previous studies, we examined the arrival timing of the preonset aurora relative to the three steps of auroral onset arc development (initial brightening, enhancement of the wave-like structure, and poleward expansion) to make the role of the preonset aurora in the auroral steps clearer. Our detailed timing analysis found that preonset auroral streamers reached the auroral onset arc but away from the initial brightening site after initial brightening for two events, while no preonset aurora reaching the initial brightening site could be identified for the other event. This result suggests that the processes associated with auroral streamers are unlikely to affect at least initial brightening, even if we consider not only the presence and arrival timing and location of the auroral streamers but also the scale of the corresponding flow and flow vortices. We list a series of open questions for testing the preonset aurora scenario further in future studies. Keywords. Magnetospheric physics (storms and substorms; auroral phenomena; magnetotail)

scholarly journals Transition from substorm growth to substorm expansion phase as observed with a radial configuration of ISTP and Cluster spacecraft

2005 ◽  
Vol 23 (6) ◽  
pp. 2183-2198 ◽  
Author(s):  
V. A. Sergeev ◽  
M. V. Kubyshkina ◽  
W. Baumjohann ◽  
R. Nakamura ◽  
O. Amm ◽  
...  
Keyword(s):  
Transition Region ◽  
Growth Phase ◽  
Plasma Sheet ◽  
Magnetic Energy ◽  
Global Scale ◽  
Substorm Onset ◽  
Plasma Injection ◽  
Storms And Substorms ◽  
Auroral Phenomena ◽  
Inner Region

Abstract. Transition from the growth phase to the substorm expansion during a well-isolated substorm with a strong growth phase is investigated using a unique radial (THEMIS-like) spacecraft constellation near midnight, including the probing of the tail current at ~16 RE with Cluster, of the transition region at ~9 RE with Geotail and Polar, and of the inner region at 6.6 RE with two LANL spacecraft. The activity development on both a global scale and near the spacecraft footpoints was monitored with global auroral images (from the IMAGE spacecraft) and the ground network. Magnetospheric models, tuned using in-situ observations, indicated a strong tail stretching and plasma sheet thinning, which included the growth of the near-Earth current (approaching 30 nA/m2) and possible formation of a local B minimum in the neutral sheet (~5 nT) at ~10–12 RE near the substorm onset. However, there were no indications that the substorm onset was initiated just in this region. We emphasize the rather weak magnetic and plasma flow perturbations observed outside the thinned plasma sheet at Cluster, which could be interpreted as the effects of localized earthward-contracting newly-reconnected plasma tubes produced by the impulsive reconnection in the midtail plasma sheet. In that case the time delays around the distinct substorm onset are consistent with the activity propagation from the midtail to the inner magnetosphere. A peculiar feature of this substorm was that 12min prior to this distinct onset, a clear soft plasma injection to the GEO orbit was recorded which has little associated effects both in the ionosphere and in the transition region at ~9 RE. This pseudo-breakup was probably due to either a localized ballooning-type activity or due to the braking of a very narrow BBF whose signatures were also recorded by Cluster. This event manifested the (previously unknown) phenomenon, a strong tail overloading (excessive storage of magnetic energy) contrasted to the modest energy dissipation and plasma acceleration, which are both discussed and interpreted as the consequences of cold/dense and thick pre-substorm plasma sheet which often occurs after the long quiet period. The lessons of using the radial spacecraft configurations in substorm onset studies are also discussed. Keywords. Magnetospheric physics (Auroral phenomena, plasma sheet, storms and substorms)

scholarly journals Thinning and expansion of the substorm plasma sheet: Cluster PEACE timing analysis

2004 ◽  
Vol 22 (12) ◽  
pp. 4165-4184 ◽  
Author(s):  
J. P. Dewhurst ◽  
C. J. Owen ◽  
A. N. Fazakerley ◽  
A. Balogh
Keyword(s):  
Plasma Sheet ◽  
Complex Dynamics ◽  
Neutral Line ◽  
Timing Analysis ◽  
Normal Component ◽  
Plasma Electron ◽  
Current Disruption ◽  
Storms And Substorms ◽  
Normal Vectors ◽  
The Given

Abstract. The storage and subsequent removal of magnetic flux in the magnetotail during a geomagnetic substorm has a dramatic effect on the thickness of the cross-tail plasma sheet. The near-Earth plasma sheet is thought to thin during the growth phase and then rapidly expand after onset of the substorm. The direction of propagation, whether earthward or tailward along the GSM-X direction in the near-Earth tail, may suggest the time ordering of current-disruption and near-Earth reconnection, both of which are key to the substorm process. Cluster's Plasma Electron And Current Experiment (PEACE) allows 4-point observations of electrons at the plasma sheet - lobe boundary as this interface passes over the Cluster tetrahedron. The relative timings of the boundary passage at each spacecraft allow a determination of this boundary's speed and direction of motion, assuming this is planar on the scale of the Cluster separation scale. For those boundaries corresponding to the expansion of the plasma sheet, this direction is fundamental to determining the direction of expansion. We present an example of isolated thinning and expansion of the plasma sheet, as well as a multiple thinning-expansion event that occurs during a more active substorm. Data from the 2001 and 2002 tail passes have been analysed and the average plasma sheet – lobe boundary normal vectors and normal component velocities have been calculated. A total of 77 crossings, typically between 10 and 20 RE downtail, correspond to substorm associated expansion of the plasma sheet over the spacecraft. These had normal vectors predominantly in the GSM-YZ plane and provided no clear evidence for the formation of the near-Earth neutral line occurring before current disruption or vice versa. The expansions of the plasma sheet generally exhibit the appropriate GSM-Z direction expected for the given lobe, and tend to have GSM-Y components that support onset occurring near the origin of the GSM-YZ plane. This result is noteworthy in that it indicates a homogeneous plasma sheet expansion. These expansions have an average velocity along their normal of 60±37kms–1. Conversely we find an average thinning velocity of 43±32kms–1 from 66 substorm-associated thinnings. The normal vectors of the thinning plasma sheet vary considerably in the GSM-YZ plane across the entire magnetotail, suggesting that more complex dynamics govern this process.Key words. Magnetospheric physics (Magnetotail; Plasma sheet; Storms and substorms)bk\\rasphone.

scholarly journals Acceleration of oxygen ions in the dynamic magnetotail

2004 ◽  
Vol 22 (4) ◽  
pp. 1305-1315 ◽  
Author(s):  
J. Birn ◽  
M. F. Thomsen ◽  
M. Hesse
Keyword(s):  
Test Particle ◽  
Plasma Sheet ◽  
Neutral Line ◽  
Mhd Simulation ◽  
Oxygen Ions ◽  
Central Plasma ◽  
Particle Orbits ◽  
Particle Simulations ◽  
Storms And Substorms ◽  
Central Plasma Sheet

Abstract. The substorm-related acceleration and flux increases of energetic oxygen ions are studied on the basis of test particle orbits in the fields obtained from an MHD simulation of plasmoid formation and ejection and the collapse (dipolarization) of the inner tail. The simulated fluxes show large anisotropies and nongyrotropic effects, phase bunching, and spatially and temporally localized beams. The energy distribution of O+ in the region of an earthward beam in the near tail becomes significantly harder, more pronounced than for protons, in qualitative agreement with observations. The simulation also shows tailward beams of energetic O+ions closely associated with the passage of a plasmoid, both inside the plasma sheet boundary and inside the central plasma sheet, consistent with observations in the far tail. The acceleration at the near-Earth x-type neutral line produces a narrow duskward beam of energetic O+ in the duskward extension of the x-line, which was not found to be as pronounced in proton test particle simulations. Key words. Magnetospheric physics (energetic particles, trapped; magnetotail; storms and substorms)

scholarly journals Modeling of nonstationary electron precipitation by the whistler cyclotron instability

1998 ◽  
Vol 16 (11) ◽  
pp. 1455-1460 ◽  
Author(s):  
A. G. Demekhov ◽  
A. A. Lyubchich ◽  
V. Y. Trakhtengerts ◽  
E. E. Titova ◽  
J. Manninen ◽  
...  
Keyword(s):  
Linear Equations ◽  
Energetic Electron ◽  
Electron Precipitation ◽  
Plasma Parameters ◽  
Wave Interactions ◽  
Cyclotron Maser ◽  
Consistent Model ◽  
Storms And Substorms ◽  
Auroral Phenomena

Abstract. We study a simple self-consistent model of a whistler cyclotron maser derived from the full set of quasi-linear equations. We employ numerical calculations to demonstrate dependencies of pulsation regimes of whistler-mode wave interactions with energetic electrons on plasma parameters. Possible temporal evolution of those regimes in real conditions is discussed; calculations are compared with case-study experimental data on energetic electron precipitation pulsations. A reasonable agreement of the model results and the observations has been found.Key words. Magnetospheric physics (Auroral phenomena; Energetic particles · precipitating; Storms and substorms)

scholarly journals Indirect mapping of the source of the oppositely directed fast plasma flows in the plasma sheet onto the auroral display

2006 ◽  
Vol 24 (2) ◽  
pp. 679-687 ◽  
Author(s):  
A. G. Yahnin ◽  
I. V. Despirak ◽  
A. A. Lubchich ◽  
B. V. Kozelov ◽  
N. P. Dmitrieva ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Plasma Sheet ◽  
Source Region ◽  
Plasma Flows ◽  
Current Disruption ◽  
Magnetic Field Model ◽  
Abstract Data ◽  
Fast Flow ◽  
Current Reduction ◽  
The Relationship

Abstract. Data from Polar and Geotail spacecraft are combined to investigate the relationship between locations of active auroras and the magnetotail plasma sheet region where reversed fast plasma flows are generated during substorms. Using the magnetospheric magnetic field model, it is shown that at the beginning of the tailward fast flow the ionospheric footprint of the spacecraft measuring the flow tends to be located poleward of the auroral bulge. The spacecraft within the earthward flow is mapped equatorward of the poleward edge of the auroral bulge. We conclude that a source of the fast plasma flows is conjugated with the poleward edge of the auroral bulge. Analysis of the behavior of the plasma and the magnetic field in the vicinity of the source of the diverging flows allows us to conclude that the source region, interpreted as the magnetic reconnection site, coincides with the region of the cross-tail current reduction, and the tailward propagation of the region is associated with the tailward propagation of the current disruption front.

Kämpfe um Bergbau und die Möglichkeiten demokratischer Transformation

2017 ◽  
Vol 47 (189) ◽  
Author(s):  
Kristina Dietz
Keyword(s):  
Direct Democracy ◽  
Social Power ◽  
Political Agenda ◽  
The Political ◽  
Liberal Democratic ◽  
Political Effects ◽  
Mining Project ◽  
National Governments ◽  
The Relationship

The article explores the political effects of popular consultations as a means of direct democracy in struggles over mining. Building on concepts from participatory and materialist democracy theory, it shows the transformative potentials of processes of direct democracy towards democratization and emancipation under, and beyond, capitalist and liberal democratic conditions. Empirically the analysis is based on a case study on the protests against the La Colosa gold mining project in Colombia. The analysis reveals that although processes of direct democracy in conflicts over mining cannot transform existing class inequalities and social power relations fundamentally, they can nevertheless alter elements thereof. These are for example the relationship between local and national governments, changes of the political agenda of mining and the opening of new spaces for political participation, where previously there were none. It is here where it’s emancipatory potential can be found.

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