| 1. |
- Phan, T. D., et al.
(författare)
-
Electron magnetic reconnection without ion coupling in Earth's turbulent magnetosheath
- 2018
-
Ingår i: Nature. - : NATURE PUBLISHING GROUP. - 0028-0836 .- 1476-4687. ; 557:7704, s. 202-
-
Tidskriftsartikel (refereegranskat)abstract
- Magnetic reconnection in current sheets is a magnetic-to-particle energy conversion process that is fundamental to many space and laboratory plasma systems. In the standard model of reconnection, this process occurs in a minuscule electron-scale diffusion region(1,2). On larger scales, ions couple to the newly reconnected magnetic-field lines and are ejected away from the diffusion region in the form of bi-directional ion jets at the ion Alfven speed(3-5). Much of the energy conversion occurs in spatially extended ion exhausts downstream of the diffusion region(6). In turbulent plasmas, which contain a large number of small-scale current sheets, reconnection has long been suggested to have a major role in the dissipation of turbulent energy at kinetic scales(7-11). However, evidence for reconnection plasma jetting in small-scale turbulent plasmas has so far been lacking. Here we report observations made in Earth's turbulent magnetosheath region (downstream of the bow shock) of an electron-scale current sheet in which diverging bi-directional super-ion-Alfvenic electron jets, parallel electric fields and enhanced magnetic-to-particle energy conversion were detected. Contrary to the standard model of reconnection, the thin reconnecting current sheet was not embedded in a wider ion-scale current layer and no ion jets were detected. Observations of this and other similar, but unidirectional, electron jet events without signatures of ion reconnection reveal a form of reconnection that can drive turbulent energy transfer and dissipation in electron-scale current sheets without ion coupling.
|
|
| 2. |
|
|
| 3. |
- Denton, R. E., et al.
(författare)
-
Determining L-M-N Current Sheet Coordinates at the Magnetopause From Magnetospheric Multiscale Data
- 2018
-
Ingår i: Journal of Geophysical Research - Space Physics. - : AMER GEOPHYSICAL UNION. - 2169-9380 .- 2169-9402. ; 123:3, s. 2274-2295
-
Tidskriftsartikel (refereegranskat)abstract
- We discuss methods to determine L-M-N coordinate systems for current sheet crossings observed by the Magnetospheric Multiscale (MMS) spacecraft mission during ongoing reconnection, where e(L) is the direction of the reconnecting component of the magnetic field, B, and e(N) is normal to the magnetopause. We present and test a new hybrid method, with e(L) estimated as the maximum variance direction of B (MVAB) and e(N) as the direction of maximum directional derivative of B, and then adjust these directions to be perpendicular. In the best case, only small adjustment is needed. Results from this method, applied to an MMS crossing of the dayside magnetopause at 1305:45UT on 16 October 2015, are discussed and compared with those from other methods for which e(N) is obtained by other means. Each of the other evaluations can be combined with e(L) from MVAB in a generalized hybrid approach to provide an L-M-N system. The quality of the results is judged by eigenvalue ratios, constancy of directions using different data segments and methods, and expected sign and magnitude of the normal component of B. For this event, the hybrid method appears to produce e(N) accurate to within less than 10 degrees. We discuss variance analysis using the electric current density, J, or the J x B force, which yield promising results, and minimum Faraday residue analysis and MVAB alone, which can be useful for other events. We also briefly discuss results from our hybrid method and MVAB alone for a few other MMS reconnection events. Plain Language Summary We discuss methods for determining coordinate systems in order to study magnetic reconnection events at the magnetopause, the boundary between the ionized gas in the region of space dominated by the Earth's magnetic field and the ionized gas coming from the solar wind. We introduce a new method that combines results from multiple methods in order to determine the three coordinate directions in space. We demonstrate this method by applying it to an event observed by the Magnetospheric Multiscale spacecraft on 16 October 2015 and at other times.
|
|
| 4. |
- Eriksson, S., et al.
(författare)
-
Magnetic island formation between large-scale flow vortices at an undulating postnoon magnetopause for northward interplanetary magnetic field
- 2009
-
Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 114:2, s. A00C17-
-
Tidskriftsartikel (refereegranskat)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.
|
|
