Structure of the separatrix region close to a magnetic reconnection X-line: Cluster observations

Abstract

[1] We use Cluster spacecraft observations to study in detail the structure of a magnetic reconnection separatrix region on the magnetospheric side of the magnetopause about 50 ion inertial lengths away from the X-line. The separatrix region is the region between the magnetic separatrix and the reconnection jet. It is several ion inertial lengths wide and it contains a few subregions showing different features in particle and wave data. One subregion, a density cavity adjacent to the separatrix, has strong electric fields, electron beams and intense wave turbulence. The separatrix region shows structures even at smaller scales, for example, solitary waves at Debye length scale. We describe in detail electron distribution functions and electric field spectra in the separatrix region and we compare them to a numerical simulation. Our observations show that while reconnection is ongoing the separatrix region is highly structured and dynamic in the electric field even if the X-line is up to 50 ion inertial lengths away.

Electron dynamics in collisionless magnetic reconnection

“…The low energy electron beam flowing into the X-line region is also detected in the boundary of the current sheet [22]. Not only these beams, but also the energetic electron beams streaming out of the X-line region were measured by the Cluster spacecraft [21,[33][34][35][36]. These observations confirmed the theoretical results for the in-plane current system, i.e.…”

Internal structure and spatial dimensions of whistler wave regions in the magnetopause boundary layer

“…The particle environment is investigated using the electron experiment PEACE (Johnstone et al, 1997) and the ion instrument CIS/CODIF (Rème et al, 1997). Both instruments can measure a 3-D distribution each spin period.…”

“…Thin electron-scale layers presumably associated with the separatrices are reported far away from the diffusion regions (e.g. André et al, 2004;Vaivads et al, 2004b andRetinò et al, 2006). Stenberg et al (2005) show that whistler mode waves observed in the boundary layer on the magnetospheric side of the magnetopause are generated in thin (electron-scale) sheets.…”

“…Today, computer simulations and spacecraft observations are beginning to resolve the fine-structure involved (e.g. Vaivads et al, 2004a;Onofri et al, 2004;Retinò et al, 2006 andMozer, 2005). Multi-spacecraft missions, such as Cluster (Escoubet et al, 1997;, offer the opportunity to resolve the spatial-temporal ambiguity associated with single spacecraft measurements and allow us to determine the scale lengths of spatial structures.…”

Three dimensional density cavities in guide field collisionless magnetic reconnection

“…The surfaces between the new magnetic regions, dividing the inflow and outflow plasmas are called separatrices. Separatrices are thin boundary layers between plasmas with different properties (density, temperature, and flow pattern) [1][2][3] and subject to instabilities, wave activity and turbulence [4][5][6]. One of the distinctive features of collisionless magnetic reconnection is the formation of localized low density regions along the separatrices [7,8].…”