| 11. |
|
|
| 12. |
- Apatenkov, S. V., et al.
(författare)
-
Conjugate observation of sharp dynamical boundary in the inner magnetosphere by Cluster and DMSP spacecraft and ground network
- 2008
-
Ingår i: Annales Geophysicae. - 0992-7689 .- 1432-0576. ; 26:9, s. 2771-2780
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate an unusual sharp boundary separating two plasma populations (inner magnetospheric plasma with high fluxes of energetic particles and plasma sheet) observed by the Cluster quartet near its perigee on 16 December 2003. Cluster was in a pearl-on-string configuration at 05:00 MLT and mapped along magnetic field lines to similar to 8-9 R-E in the equatorial plane. It was conjugate to the MIRACLE network and the DMSP F16 spacecraft passed close to Cluster footpoint. The properties of the sharp boundary, repeatedly crossed 7 times by five spacecraft during similar to 10 min, are: (1) upward FAC sheet at the boundary with similar to 30 nA/m(2) current density at Cluster and similar to 2000 nA/m(2) at DMSP; (2) the boundary had an embedded layered structure with different thickness scales, the electron population transition was at similar to 20 km scale at Cluster (<7 km at DMSP), proton population had a scale similar to 100 km, while the FAC sheet thickness was estimated to be similar to 500 km at Cluster (similar to 100 km at DMSP); (3) the boundary propagated in the earthward-eastward direction at similar to 8 km/s in situ (equatorward-eastward similar to 0.8 km/s in ionosphere), and then decelerated and/or stopped. We discuss the boundary formation by the collision of two different plasmas which may include dynamical three-dimensional field-aligned current loops.
|
|
| 13. |
- Apatenkov, S. V., et al.
(författare)
-
Multi-spacecraft observation of plasma dipolarization/injection in the inner magnetosphere
- 2007
-
Ingår i: Annales Geophysicae. - 0992-7689 .- 1432-0576. ; 25:3, s. 801-814
-
Tidskriftsartikel (refereegranskat)abstract
- Addressing the origin of the energetic particle injections into the inner magnetosphere, we investigate the 23 February 2004 substorm using a favorable constellation of four Cluster (near perigee), LANL and Geotail spacecraft. Both an energy-dispersed and a dispersionless injection were observed by Cluster crossing the plasma sheet horn, which mapped to 9-12 R-E in the equatorial plane close to the midnight meridian. Two associated narrow equatorward auroral tongues/streamers propagating from the oval poleward boundary could be discerned in the global images obtained by IMAGE/WIC. As compared to the energy-dispersed event, the dispersionless injection front has important distinctions consequently repeated at 4 spacecraft: a simultaneous increase in electron fluxes at energies similar to 1.300 keV, similar to 25 nT increase in B-Z and a local increase by a factor 1.5-1.7 in plasma pressure. The injected plasma was primarily of solar wind origin. We evaluated the change in the injected flux tube configuration during the dipolarization by fitting flux increases observed by the PEACE and RAPID instruments, assuming adiabatic heating and the Liouville theorem. Mapping the locations of the injection front detected by the four spacecraft to the equatorial plane, we estimated the injection front thickness to be similar to 1 R-E and the earthward propagation speed to be similar to 200-400km/s (at 9-12 RE). Based on observed injection properties, we suggest that it is the underpopulated flux tubes (bubbles with enhanced magnetic field and sharp inner front propagating earthward), which accelerate and transport particles into the strong-field dipolar region.
|
|
| 14. |
- Horbury, T., et al.
(författare)
-
Cross-scale : A multi-spacecraft mission to study cross-scale coupling in space plasmas
- 2006
-
Ingår i: European Space Agency, (Special Publication) ESA SP. ; , s. 561-568
-
Konferensbidrag (refereegranskat)abstract
- Collisionless astrophysical plasmas exhibit complexity on many scales: if we are to understand their properties and effects, we must measure this complexity. We can identify a small number of processes and phenomena, one of which is dominant in almost every space plasma region of interest: shocks, reconnection and turbulence. These processes act to transfer energy between locations, scales and modes. However, this transfer is characterised by variability and 3D structure on at least three scales: electron kinetic, ion kinetic and fluid. It is the nonlinear interaction between physical processes at these scales that is the key to understanding these phenomena and predicting their effects. However, current and planned multi-spacecraft missions such as Cluster and MMS only study variations on one scale in 3D at any given time - we must measure the three scales simultaneously fully to understand the energy transfer processes. We propose a mission, called Cross-Scale, to study these processes. Cross-Scale would comprise three nested groups, each consisting of up to four spacecraft. Each group would have a different spacecraft separation, at approximately the electron and ion gyroradii, and a larger MHD scale. We would therefore be able to measure variations on all three important physical scales, simultaneously, for the first time. The spacecraft would fly in formation through key regions of near-Earth space: The solar wind, bowshock, magnetosheath, magnetopause and magnetotail.
|
|
| 15. |
- Pedersen, A., et al.
(författare)
-
Electron density estimations derived from spacecraft potential measurements on Cluster in tenuous plasma regions
- 2008
-
Ingår i: Journal of Geophysical Research. - : American Geophysical Union (AGU). - 0148-0227 .- 2156-2202. ; 113:A7
-
Tidskriftsartikel (refereegranskat)abstract
- Spacecraft potential measurements by the EFW electric field experiment on the Cluster satellites can be used to obtain plasma density estimates in regions barely accessible to other type of plasma experiments. Direct calibrations of the plasma density as a function of the measured potential difference between the spacecraft and the probes can be carried out in the solar wind, the magnetosheath, and the plasmashere by the use of CIS ion density and WHISPER electron density measurements. The spacecraft photoelectron characteristic ( photoelectrons escaping to the plasma in current balance with collected ambient electrons) can be calculated from knowledge of the electron current to the spacecraft based on plasma density and electron temperature data from the above mentioned experiments and can be extended to more positive spacecraft potentials by CIS ion and the PEACE electron experiments in the plasma sheet. This characteristic enables determination of the electron density as a function of spacecraft potential over the polar caps and in the lobes of the magnetosphere, regions where other experiments on Cluster have intrinsic limitations. Data from 2001 to 2006 reveal that the photoelectron characteristics of the Cluster spacecraft as well as the electric field probes vary with the solar cycle and solar activity. The consequences for plasma density measurements are addressed. Typical examples are presented to demonstrate the use of this technique in a polar cap/lobe plasma.
|
|
| 16. |
|
|
| 17. |
|
|
| 18. |
- Palin, Laurianne, et al.
(författare)
-
Three-dimensional current systems and ionospheric effects associated with small dipolarization fronts
- 2015
-
Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 120:5, s. 3739-3757
-
Tidskriftsartikel (refereegranskat)abstract
- We present a case study of eight successive plasma sheet (PS) activations (usually referred to as bursty bulk flows or dipolarization fronts), associated with small individual B-ZGSM increases on 31 March 2009 (0200-0900 UT), observed by the Time History of Events and Macroscale Interactions During Substorms mission. This series of events happens during very quiet solar wind conditions, over a period of 7 h preceding a substorm onset at 1230 UT. The amplitude of the dipolarizations increases with time. The low-amplitude dipolarization fronts are associated with few (1 or 2) rapid flux transport events (RFT, E-h > 2 mV/m), whereas the large-amplitude ones encompass many more RFT events. All PS activations are associated with small and localized substorm current wedge (SCW)-like current system signatures, which seems to be the consequence of RFT arrival in the near tail. The associated ground magnetic perturbations affect a larger part of the contracted auroral oval when, in the magnetotail, more RFT are embedded in PS activations (> 5). Dipolarization fronts with very low amplitude, a type usually not included in statistical studies, are of particular interest because we found even those to be associated with clear small SCW-like current system and particle injections at geosynchronous orbit. This exceptional data set highlights the role of flow bursts in the magnetotail and leads to the conclusion that we may be observing the smallest form of a substorm or rather its smallest element. This study also highlights the gradual evolution of the ionospheric current disturbance as the plasma sheet is observed to heat up.
|
|
| 19. |
- Grigorenko, E. E., et al.
(författare)
-
THEMIS observations of the current sheet dynamics in response to the intrusion of the high-velocity plasma flow into the near-Earth magnetotail
- 2014
-
Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 119:8
-
Tidskriftsartikel (refereegranskat)abstract
- A small separation between Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes allows us to analyze a sudden activation in the near-Earth current sheet (CS) at microscales. The start of the activation coincides with the appearance of an earthward plasma flow and dipolarization front (DF) at THEMIS location. The time sequence of observations of the fast plasma flow and the associated DF by three THEMIS probes denotes their dawnward displacement and the localization of the flow channel in the dawn-dusk direction. The onset of kink perturbations of the CS was generated on the dawn side of the flow. These fluctuations also propagated dawnward and were followed by the CS thinning (L similar to rho(i)) and by the development of tearing instability with transient appearance of a magnetic null point. The region of the unstable CS with a magnetic null point was localized in the X and, possibly, in the Y directions. The CS perturbations were most likely triggered by the intrusion of the fast flow into the ambient plasma in the course of the global dawnward displacement of the flow structure. Although no substorm onset was observed during the CS activation, a ground signature of a pseudobreakup was detected just after the excitement of the tearing mode in the near-Earth tail. Probably the pseudobreakup was caused by a localized diversion of the current, which could result from the disruption of the cross-tail current in a localized region of the near-Earth CS.
|
|
