Spatial Scales and Structure of Dipolarisation Fronts using Multispaceraft Observations

Simultaneous observation by closely spaced satellites are used to identify the spatial scales of the electric and magnetic fields of nonlinear structures and waves associated with dipolarisation fronts. The statistical results obtained are compared with theoretical models for the interaction of plasma particles with the front structure. In addition to the front itself, the spatial structure of magnetic holes that occasionally occur in conjunction with dipolarisation fronts and have been previously observed by THEMIS is analysed and compared with the interpretation of these structures as remnants of nonlinear mirror waves or as resulting from the tearing instability. It is shown that the observed properties of these magnetic holes are inconsistent with the results of the mirror instability.