Satellite observations of separator-line geometry of three-dimensional magnetic reconnection.

Detection of a separator line that connects magnetic nulls and the determination of the dynamics and plasma environment of such a structure can improve our understanding of the three-dimensional (3D) magnetic reconnection process. However, this type of field and particle configuration has not been directly observed in space plasmas. Here we report the identification of a pair of nulls, the null–null line that connects them, and associated fans and spines in the magnetotail of the Earth using data from the four Cluster spacecraft. With di and de designating the ion and electron inertial lengths, respectively, the separation between the nulls is found to be ∼0.7±0.3d_i and an associated oscillation is identified as a lower-hybrid wave with wavelength ∼d_e. This in situ evidence of the full 3D reconnection geometry and associated dynamics provides an important step towards establishing an observational framework of 3D reconnection. [ABSTRACT FROM AUTHOR]