Three‐dimensional dynamics of vortex‐induced reconnection and comparison with THEMIS observations

Abstract

[1] The entry of solar wind into the magnetosphere is strongly influenced by kinetic-scale boundary layers where the rapid variation in the magnetic field and/or velocity can drive transport. In current layers with strong Alfvénic velocity shear, the generation of vortices from the Kelvin-Helmholtz instability can drive magnetic reconnection even in broader current sheets by locally compressing these layers as the vortices develop. Previous two-dimensional (2-D) fully kinetic simulations of this vortex-induced reconnection process have demonstrated the copious formation of magnetic islands in regions of strongly compressed current between the vortices. Here we describe the first three-dimensional (3-D) fully kinetic simulations of this process and demonstrate that the compressed current sheets give rise to magnetic flux ropes over a range of oblique angles and along the entire extent of the compressed current layer around the periphery of the vortex. These flux ropes propagate with the shear flow and eventually merge with the vortex. Over longer time scales, this basic scenario is repeated as the vortices drive new compressed current sheets. In the final stage, the vortices undergo a merging process that drives new compressed current sheets and flux ropes. Based on these simulations, a simple model is proposed that predicts the size of these flux ropes relative to their parent vortex. Both the relative sizes as well as the structure of the profiles across the vortex are in reasonable agreement with Time History of Events and Macroscale Interactions (THEMIS) observations at the Earth's low-latitude magnetopause.

Magnetic depression and electron transport in an ion-scale flux rope associated with Kelvin–Helmholtz waves

“…3a), and its duration is about 2.7 s ( T FR ). The axis direction of this flux rope is consistent with previous full kinetic simulations, which showed flux ropes were formed along the periphery of the vortex (Nakamura et al, 2013). The field magnitude dip at the center of this flux rope suggests it is a crater flux rope, which is accompanied by a plasma density peak (Fig.…”

“…Small-scale flux ropes, identified primarily by magnetic bipolar structures, have been observed at the trailing edges of Kelvin-Helmholtz (KH) waves (e.g., Eriksson et al, 2009;Nakamura et al, 2013), where local conditions could be favorable for magnetic reconnection ). However, due to the limitation of temporal resolutions, such observations had been unable to provide direct and conclusive evidence.…”

Spatial dimensions of the electron diffusion region in anti-parallel magnetic reconnection

“…Although this paper treated an anti-parallel magnetic field configuration, effects of the guide magnetic field component, which often exists for the dayside reconnection (e.g., Swisdak et al, 2003;Hesse, 2006) or the vortex-induced reconnection (e.g., Nakamura et al, 2013) at the Earth's magnetopause, should be examined to more generally understand the structure of the electron diffusion region. Since electrons are more strongly magnetized even near the X-point when considering the guide field, the orbit of electrons near the Xpoint and the associated structure of the non-gyrotropic region would significantly be affected by the guide field as indicated in past kinetic studies (e.g., Horiuchi and Sato, 1997;Ricci et al, 2004;Swisdak et al, 2005;Hesse, 2006).…”

The Earth: Plasma Sources, Losses, and Transport Processes

“…Faganello et al (2014) published a case study providing observational evidence for the occurrence of this scenario using THEMIS spacecraft data. There may not yet be a consensus on this scenario, as the same THEMIS data were also used to provide support for an interpretation involving reconnection at low latitudes and sub-vortex scales, according to three-dimensional fully kinetic simulations by Nakamura et al (2013).…”