| 1. |
- Angelopoulos, V., et al.
(author)
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First Results from the THEMIS Mission
- 2008
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In: Space Science Reviews. - : Springer Science and Business Media LLC. - 0038-6308 .- 1572-9672. ; 141:1-4, s. 453-476
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Research review (peer-reviewed)abstract
- THEMIS was launched on February 17, 2007 to determine the trigger and large-scale evolution of substorms. During the first seven months of the mission the five satellites coasted near their injection orbit to avoid differential precession in anticipation of orbit placement, which started in September 2007 and led to a commencement of the baseline mission in December 2007. During the coast phase the probes were put into a string-of-pearls configuration at 100 s of km to 2 R-E along-track separations, which provided a unique view of the magnetosphere and enabled an unprecedented dataset in anticipation of the first tail season. In this paper we describe the first THEMIS substorm observations, captured during instrument commissioning on March 23, 2007. THEMIS measured the rapid expansion of the plasma sheet at a speed that is commensurate with the simultaneous expansion of the auroras on the ground. These are the first unequivocal observations of the rapid westward expansion process in space and on the ground. Aided by the remote sensing technique at energetic particle boundaries and combined with ancillary measurements and MHD simulations, they allow determination and mapping of space currents. These measurements show the power of the THEMIS instrumentation in the tail and the radiation belts. We also present THEMIS Flux Transfer Events (FTE) observations at the magnetopause, which demonstrate the importance of multi-point observations there and the quality of the THEMIS instrumentation in that region of space.
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| 2. |
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| 3. |
- Andersson, L., et al.
(author)
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New Features of Electron Phase Space Holes Observed by the THEMIS Mission
- 2009
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 102:22, s. 225004-
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Journal article (peer-reviewed)abstract
- Observations of electron phase-space holes (EHs) in Earth's plasma sheet by the THEMIS satellites include the first detection of a magnetic perturbation (delta B-parallel to) parallel to the ambient magnetic field (B-0). EHs with a detectable delta B-parallel to have several distinguishing features including large electric field amplitudes, a magnetic perturbation perpendicular to B-0, high speeds (similar to 0.3c) along B-0, and sizes along B-0 of tens of Debye lengths. These EHs have a significant center potential (Phi similar to k(B)T(e)/e), suggesting strongly nonlinear behavior nearby such as double layers or magnetic reconnection.
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| 4. |
- Ergun, R. E., et al.
(author)
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Observations of Double Layers in Earth's Plasma Sheet
- 2009
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 102:15, s. 155002-
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Journal article (peer-reviewed)abstract
- We report the first direct observations of parallel electric fields (E-parallel to) carried by double layers (DLs) in the plasma sheet of Earth's magnetosphere. The DL observations, made by the THEMIS spacecraft, have E-parallel to signals that are analogous to those reported in the auroral region. DLs are observed during bursty bulk flow events, in the current sheet, and in plasma sheet boundary layer, all during periods of strong magnetic fluctuations. These observations imply that DLs are a universal process and that strongly nonlinear and kinetic behavior is intrinsic to Earth's plasma sheet.
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| 5. |
- Johansson, T., et al.
(author)
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Observation of an inner magnetosphere electric field associated with a BBF-like flow and PBIs
- 2009
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In: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 27:4, s. 1489-1500
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Journal article (peer-reviewed)abstract
- Themis E observed a perpendicular (to the magnetic field) electric field associated with an Earthward plasma flow at XGSM=-9.6 R-E on 11 January 2008. The electric field observation resembles Cluster observations closer to Earth in the auroral region. The fast plasma flow shared some characteristics with bursty bulk flows (BBFs) but did not meet the usual criteria in maximum velocity and duration to qualify as one. Themis C observed the same flow further downtail but Themis D, separated by only 1 R-E in azimuthal direction from Themis E, did not. At the time of the electric field and ion flow event, the all-sky imager and ground-based magnetometer at Rankin Inlet observed Poleward Boundary Intensifications (PBIs) and a negative bay signature. None of the other Themis ground-based observatories recorded any significant auroral or magnetic field activity, indicating that this was a localized activity. The joint Themis in situ and ground-based observations suggest that the two observations are related. This indicates that auroral electric fields can extend to regions much farther out than previously seen in Cluster observations.
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| 6. |
- Eastwood, J. P., et al.
(author)
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THEMIS observations of a hot flow anomaly : Solar wind, magnetosheath, and ground-based measurements
- 2008
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In: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 35:17, s. L17S03-
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Journal article (peer-reviewed)abstract
- The THEMIS spacecraft encountered a Hot Flow Anomaly ( HFA) on the dusk flank of the Earth's bow shock on 4 July 2007, observing it on both sides of the shock. Meanwhile, the THEMIS ground magnetometers traced the progress of the associated Magnetic Impulse Event along the dawn flank of the magnetosphere, providing a unique opportunity to study the transmission of the HFA through the shock and the subsequent downstream response. THEMIS-A, in the solar wind, observed classic HFA signatures. Isotropic electron distributions inside the upstream HFA are attributed to the action of the electron firehose instability. THEMIS-E, just downstream, observed a much more complex disturbance with the pressure perturbation decoupled from the underlying discontinuity. Simple calculations show that the pressure perturbation would be capable of significantly changing the magnetopause location, which is confirmed by the ground-based observations.
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| 7. |
- Eriksson, S., et al.
(author)
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Magnetic island formation between large-scale flow vortices at an undulating postnoon magnetopause for northward interplanetary magnetic field
- 2009
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In: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 114:2, s. A00C17-
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Journal article (peer-reviewed)abstract
- Time History of Events and Macroscale Interactions during Substorms multispacecraft observations are presented for a similar to 2-h-long postnoon magnetopause event on 8 June 2007 that for the first time indicate that the trailing (sunward) edges of Kelvin-Helmholtz (KH) waves are commonly related to small-scale < 0.56 R-E magnetic islands or flux transfer events (FTE) during the growth phase of these surface waves. The FTEs typically show a characteristic bipolar B-N structure with enhanced total pressure at their center. Most of the small-scale FTEs are not related to any major plasma acceleration. TH-A observations of one small FTE at a transition from the low-latitude boundary layer (LLBL) into a magnetosheath plasma depletion layer were reconstructed using separate techniques that together confirm the presence of a magnetic island within the LLBL adjacent to the magnetopause. The island was associated with a small plasma vortex and both features appeared between two large-scale (similar to 1 R-E long and 2000 km wide) plasma vortices. We propose that the observed magnetic islands may have been generated from a time-varying reconnection process in a low ion plasma beta (beta(i) < 0.2) and low 8.3 degrees field shear environment at the sunward edge of the growing KH waves where the local magnetopause current sheet may be compressed by the converging flow of the large-scale plasma vortices as suggested by numerical simulations of the KH instability.
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| 8. |
- Hamrin, Maria, et al.
(author)
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Observations of concentrated generator regions in the nightside magnetosphere by Cluster/FAST conjunctions
- 2006
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In: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 24, s. 637-49
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Journal article (peer-reviewed)abstract
- Here and in the companion paper, Marghitu et al. (2006), we investigate plausible auroral generator regions in the nightside auroral magnetosphere. In this article we use magnetically conjugate data from the Cluster and the FAST satellites during a 3.5-h long event from 19-20 September 2001. Cluster is in the Southern Hemisphere close to apogee, where it probes the plasma sheet and lobe at an altitude of about 18 RE. FAST is below the acceleration region at approximately 0.6 RE. Searching for clear signatures of negative power densities, E(.)J < O, in the Cluster data we can identify three concentrated generator regions (CGRs) during our event. From the magnetically conjugate FAST data we see that the observed generator regions in the Cluster data correlate with auroral precipitation. The downward Poynting flux observed by Cluster, as well as the scale size of the CGRs, are consistent with the electron energy flux and the size of the inverted-V regions observed by FAST. To our knowledge, these are the first in-situ observations of the crossing of an auroral generator region. The main contribution to E(.)J < O comes from the GSE E(y)J(y). The electric field E-y is weakly negative during most of our entire event and we conclude that the CGRs occur when the duskward current J(y) grows large and positive. We find that our observations are consistent with a local southward expansion of the plasma sheet and/or rather complicated, 3-D wavy structures propagating over the Cluster satellites. We find that the plasma is working against the magnetic field, and that kinetic energy is being converted into electromagnetic energy. Some of the energy is transported away as Poynting flux.
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| 9. |
- Marghitu, O., et al.
(author)
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Auroral arc and oval electrodynamics in the Harang region
- 2009
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In: Journal of Geophysical Research. - : American Geophysical Union (AGU). - 0148-0227 .- 2156-2202. ; 114
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Journal article (peer-reviewed)abstract
- Auroral arcs are typically described in terms of an upward field-aligned current (FAC) sheet above the arc, connected by ionospheric Pedersen current to a downward FAC sheet near the arc. On the basis of data measured by the FAST spacecraft, conjugate with ground optical observations, we present first a wide and stable winter evening arc, where this standard model does not apply. The arc is observed in the Harang region during the growth phase of a modest substorm, poleward of the convection reversal (CR) boundary. Although the magnetic field data suggest the typical configuration, the two FAC sheets appear to be decoupled near the satellite footprint: the upward FAC is fed by the westward electrojet (WEJ), while the downward FAC feeds the eastward electrojet (EEJ). The examination of the arc by the newly developed ALADYN technique confirms this peculiar current topology. For comparison, we apply ALADYN also to a second evening arc, located within the Harang region equatorward from the CR. The arc is confirmed to have the standard configuration, consistent with a former study, but substantial FAC-EJ coupling is inferred in the auroral oval both poleward and equatorward of the arc. A key element for the topology of the current closure is the westward component of the electric field, which influences the relative location of the CR with respect to the large-scale FAC reversal (FR) boundary. As proved by tests on synthetic data, a westward component of the electric field pushes the CR toward the FR, preventing thus the standard FAC closure, while the conductance and FAC pattern shape the CR profile. Since a westward electric field is often measured in the Harang region, the FAC-EJ coupling is expected to be an essential ingredient there. This has important implications for the current closure in the equatorial magnetosphere and for the auroral current circuit in the WEJ region, closely related to the substorm process.
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| 10. |
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