Final Report

Current sheet occurs in space plasmas at boundaries between different plasma and/or magnetic field regions.  They are important sites of energy conversion processes having large-scale consequences such as magnetic storms and substorms, which are one of the important manifestation of the space weather.   Among the different current sheet processes magnetic reconnection is an important process for mixing and acceleration of plasmas and is identified throughout the solar system including  Earth and different planetary environments, in solar flares as well as in solar wind.  Recent multi-spacecraft observations by ESA mission Cluster and NASA mission THEMIS provided ideal data for studying the current sheet in the Earth's magnetotail.   The Cluster consists of four spacecraft forming a tetrahedra configuration, which allows to determine gradients in a 3D space. The five THEMIS spacecraft are separated by larger distances, simultaneously covering different regions in the magnetotail current sheet, and enables to study changes of large-scale magnetotail configuration. In this project we used data from these complementary mission to analyze large-scale evolution of the thin current sheet as well as the local activation processes of the current sheets.   

By applying multi-point data analysis methods, we have obtained evolution of the large-scale thin current sheet from times before it started to activate and during the times of transient and localized changes of the magnetic structures. In particular, we identified the drastic temporal/spatial changes in the magnetic field component normal to the current sheet that redistribute to form a localized thin current sheet region before its activation.  Such configuration leads to instabilities causing magnetic reconnection, where the magnetic field energy is converted to particle energy resulting in high-speed plasma flows.  Based on detailed event analysis, by reconstructing the current sheet structures, we also found a new type of thin current sheet in the magnetic reconnection events with a weak magnetic field component along the background tail current direction. Furthermore, new types of small-scale magnetic flux ropes (spiral magnetic field structures) outside the center of the current sheets are identified.  These unexpected dynamical 3D signatures obtained in the reconnection current sheets have important implications also for simulation/theoretical work and will serve as an important reference for the future Magnetospheric Multiscale Mission (MMS).