Merging 4 spacecraft data: Concepts used for analysing discontinuities

Shocks and discontinuities in space plasmas have received much attention in both theoretical studies and spacecraft data analyses. The advent of multi-spacecraft missions, such as ISEE, have provided for a vast improvement of experimental information available on these structures. The ESA CLUSTER, multi-spacecraft mission presents the community with a unique opportunity to investigate these structures with considerably more information than in previous missions. The objective of the current study is to consider the balance of information on the topology and motion of these structures, gained from four probe (CLUSTER) array data (but also from less than four spacecraft arrays). In particular, this balance is reviewed with regard to the order (or complexity) of the information sought in relation to the uncertainties involved in the determination. Typical magnetic field signatures computed from simulated trajectories through simple planar and curved discontinuity models are used as input data to the tool. This allows us to grasp several subtleties arising from competing influences of the physical properties reflected in the data, for example curvature and acceleration. In this way we propose a sophisticated discontinuity analysis tool for CLUSTER. (C) 1997 COSPAR. Published by Elsevier Science Ltd.