Electron dynamics and magnetotail structure

The Earth`s magnetosphere is formed as a consequence of the interaction between the solar wind and the terrestrial magnetic field. The stress applied by the solar wind on the Earths magnetic field results in a prolonged night-side magnetosphere, called the magnetotail, with a cross tail current sheet centered in the midst of the plasma sheet that separates two domains of the oppositely directed magnetic fields. Two multi- point spacecraft missions, Cluster and THEMIS, are providing a significant new capability of in-situ observations of space plasma by differentiating spatial structures from temporal changes. By using data from Cluster and THEMIS, combined with empirical and theoretical modeling, we have studied the evolution and structure of the thin current sheets in a previous joint project (I429-N16). Characteristics of ion-scale current sheets during quiet times as well as during reconnection events were determined. Accurate spatial gradients have been compared with particle measurements to confirm the leading role of non-adiabatic ions in formation of the current sheet. In order to resolve the electron-scale process in a thin current sheet, however, data from the current mission are limited in spatial and temporal resolution, and therefore require specific treatment of data or assumption in the orientation or motion of the structures. It became clear that for further understanding magnetotail dynamics, better electron observations, in particular three-dimensional distribution functions, are essential. This will be the focus of the proposed project. Furthermore, a new opportunity of resolving electron processes will arise with the launch of a new mission, NASAs Magnetospheric MultiScale (MMS), in late 2014. In this proposal, we will study multi-scale processes determining magnetotail structure and dynamics based on data analysis of the ongoing multi-point missions, Cluster and THEMIS, combined with MMS by focusing on the electron dynamics. The key science questions are: 1. How do electrons contributes to the evolution of different current sheet disturbances? 2. What is the role of the electrons in determining the large-scale structure of the magnetotail? The uniqueness of the projects is that we study the multi-scale context of magnetospheric disturbances by analyzing the electrons in different ways. Field-aligned electron processes, including the coupling to the ionosphere (an important source and sink of magnetospheric particles) will also be investigated. The IWF and IKI teams have rich experience in this kind of data analysis and have a long collaboration record. The obtained results will stimulate new theoretical work in the field and are expected to not only further our understanding the plasma processes in the Earth`s magnetotail, but in other planetary tail or in any wake structure of the magnetized body in space plasma.

Electron dynamics and magnetotail structure Summary The space is filled with plasma, an ionized high-temperature tenuous gas that consists of electrons and protons and other ions, interacting with magnetic/electric field. The Earth's magnetosphere is formed as a consequence of the interaction between the solar wind plasma flows, that carry interplanetary magnetic field, and the terrestrial magnetic field and plasmas. The prolonged night-side magnetosphere is called the magnetotail, which is the target region of the research in this project. In this project, we studied micro-scale as well as global processes determining magnetotail structure and dynamics based on data analysis of the ongoing multi-point spacecraft missions, ESA's Cluster and NASA's THEMIS and MMS mission. In particular, we focused on the dynamics of electrons, which is the fastest and lightest plasma component. Electrons dynamics has been less known due to the difficulties of an accurate measurement, but become possible to analyze in detail with the launch of MMS in 2015. Plasma including both electrons and ions, magnetic, and electric field data were analyzed by performing different analysis methods, partly developed in the project, for multi-point spacecraft data. The results from observations were compared with those from numerical simulation, which is an useful tool to confirm the underlying physical mechanisms inferred from local observations in space. Among different processes in the magnetotail, we studied dynamic processes such as magnetic reconnection, where magnetic energy is converted to particle energy accompanied by topological change in magnetic field that leads to a large-scale consequence, called substorm/storms, which is manifested as spectacular aurora and enhancements in energetic particles in the near-Earth, called injection. With the help of unprecedented high-resolution data from MMS, we could for the first time reveal the electron acceleration in a near-2D symmetric magnetic reconnection region in a quantitative way supported also by the results from the full particle kinetic simulation. We could further reveal the field-aligned electron processes, including the coupling to the ionosphere (an important source and sink of magnetospheric particles). Electron dynamics and large-scale magnetotail structure plays an important role in the explosive energy transfer during substorms and storms, which are one of important space weather phenomena that affects significantly our technology life for communication and navigation.