Small scale magnetic structures: Cluster observations

Within the inner magnetosphere the occurrence of plasma waves and/or magnetic field structures play an important role in the dynamics of the particle populations, accelerating some particles to higher energies while scattering others. The 2013 Cluster Inner Magnetosphere Campaign was designed to investigate these process based on observations made at small separation scales. In addition, it provides an ideal opportunity for the study of small scale structures. This paper presents observations of previously unreported small scale magnetic field structures and investigates their characteristics and spatial properties. These structures, seen in the STAFF-SC data set, are characterised by a rotation in the field direction and are observed to have spatial sizes of a few 10’s of km, with a central core region around 10 km and are probably filamentary current structures. Using a variance analysis, it was determined that the maximum variance direction was close to being perpendicular to the external magnetic field. Based on the size of the central core region the current density is of the order of 10-40 nAm−2. While they may affect the profile of these structures, data calibration effects were ruled out as their origin.