Statistical Properties of Magnetic Structures and Energy Dissipation during Turbulent Reconnection in the Earth's Magnetotail

Abstract

We present the first statistical study of magnetic structures and associated energy dissipation observed during a single period of turbulent magnetic reconnection, by using the in situ measurements of the Magnetospheric Multiscale mission in the Earth's magnetotail on 26 July 2017. The structures are selected by identifying a bipolar signature in the magnetic field and categorized as plasmoids or current sheets via an automated algorithm which examines current density and plasma flow. The size of the plasmoids forms a decaying exponential distribution ranging from subelectron up to ion scales. The presence of substantial number of current sheets is consistent with a physical picture of dynamic production and merging of plasmoids during turbulent reconnection. The magnetic structures are locations of significant energy dissipation via electric field parallel to the local magnetic field, while dissipation via perpendicular electric field dominates outside of the structures. Significant energy also returns from particles to fields. Plain Language Summary Magnetic reconnection is an important mechanism for generating energetic particles in space and solar environments. Turbulent magnetic reconnection causes the development of many small-scale magnetic structures, such as locally helical or loop-like magnetic fields (plasmoids), or areas where oppositely directed magnetic fields are sandwiched together (current sheets). The exact formation and distribution of the structures, as well as the role the structures play in particle energization and the evolution of magnetic reconnection, is still unknown. Using data from the Magnetospheric Multiscale (MMS) mission, we developed an algorithm that is able to detect and identify the magnetic structures present in a region of turbulent magnetic reconnection. The number of structures was found to decrease with size as a decaying exponential, which is consistent with previous theories. The structures contributed strongly to the energization of particles parallel to the local magnetic field, but were not significant sites of energization overall. Overall energization is dominated by energization perpendicular to the local field outside of these structures. There is also significant energy return from particles to the fields.

Statistic Properties of Electron Energy Enhancement During the Inner Electron Diffusion Region Crossing

“…(2013). On the other hand, one can also find the observation results which have a similar energy conversion allocation between parallel and perpendicular parts (e.g., Bergstedt et al., 2020).…”

“…Assisted with our simulation which uses higher grid resolution, the perpendicular dominant pressure anisotropy within the inner EDR can be revealed more distinctively than the results shown in Figure 12a of Egedal et al (2013). On the other hand, one can also find the observation results which have a similar energy conversion allocation between parallel and perpendicular parts (e.g., Bergstedt et al, 2020).…”

Properties and Acceleration Mechanisms of Electrons Up To 200 keV Associated With a Flux Rope Pair and Reconnection X‐Lines Around It in Earth's Plasma Sheet

“…The most probable $${W}_{\mathrm{c}\mathrm{h}\mathrm{a}\mathrm{o}\mathrm{t}\mathrm{i}\mathrm{c}}$$ was as high as 3 MeV. This is because the strong helical magnetic field lines in the flux ropes correspond to large curvature radii of the magnetic field lines (e.g., Bergstedt et al., 2020; Shen et al., 2007; Sun et al., 2019; Y. C. Zhang et al., 2013), which in turn results in high $${W}_{\mathrm{c}\mathrm{h}\mathrm{a}\mathrm{o}\mathrm{t}\mathrm{i}\mathrm{c}}$$. The electrons in the energy range from ∼50 to 200 keV investigated here were in regular orbit inside the flux ropes.…”

“…These observations might indicate that the magnetic field and plasma process are turbulent during this interval around the flux rope, which might be driven by the frequently appearing reconnection X-lines surrounding the flux rope pair. In the turbulent plasma sheet, as shown in Bergstedt et al (2020) and Ergun et al (2020a), significant electromagnetic field energy is observed to be converted to particles, however, a large fraction of energy can return from particles to the electromagnetic field.…”

Magnetic reconnection in the era of exascale computing and multiscale experiments

“…Observationally, there is ample direct in-situ evidence for the existence of multiple X-line regime in Earth's magnetosphere [101][102][103] and indirect evidence from remote-sensing solar observations 104,105 . However, the limited statistical studies of these observations as well as from the laboratory (see below) suggest exponential distributions 96,[106][107][108][109][110][111] . It is unclear why this qualitative discrepancy exists, but multi-spacecraft missions with in-situ measurements, such as the current Magnetospheric MultiScale (MMS) mission 32 with many more satellites are required to better observe multiscale reconnection phenomena.…”