Analysis of thick, non-planar boundaries using the discontinuity analyser

Abstract

The advent of missions comprised of phased arrays of spacecraft, with separation distances ranging down to at least mesoscales, provides the scienti®c community with an opportunity to accurately analyse the spatial and temporal dependencies of structures in space plasmas. Exploitation of the multi-point data sets, giving vastly more information than in previous missions, thereby allows unique study of their small-scale physics. It remains an outstanding problem, however, to understand in what way comparative information across spacecraft is best built into any analysis of the combined data. Dierent investigations appear to demand dierent methods of data co-ordination. Of the various multispacecraft data analysis techniques developed to aect this exploitation, the discontinuity analyser has been designed to investigate the macroscopic properties (topology and motion) of boundaries, revealed by multi-spacecraft magnetometer data, where the possibility of at least mesoscale structure is considered. It has been found that the analysis of planar structures is more straightforward than the analysis of non-planar boundaries, where the eects of topology and motion become interwoven in the data, and we argue here that it becomes necessary to customise the analysis for non-planar events to the type of structure at hand. One issue central to the discontinuity analyser, for instance, is the calculation of normal vectors to the structure. In the case of planar and`thin' non-planar structures, the method of normal determination is well-de®ned, although subject to uncertainties arising from unwanted signatures. In the case of`thick', non-planar structures, however, the method of determination becomes particularly sensitive to the type of physical sampling that is present. It is the purpose of this article to ®rstly review the discontinuity analyser technique and secondly, to discuss the analysis of the normals to thick non-planar structures detected in magnetometer data.

Thinning and expansion of the substorm plasma sheet: Cluster PEACE timing analysis

“…There are several methods for the analysis of boundaries between different fields and plasma populations using multispacecraft data (Dunlop and Woodward, 1999;Harvey, 2000;Haaland et al, 2004). Dunlop and Woodward (1999) make use of four-point magnetic field minimum variance analysis vectors to obtain a description of non-planar, accelerating boundaries.…”

“…Dunlop and Woodward (1999) make use of four-point magnetic field minimum variance analysis vectors to obtain a description of non-planar, accelerating boundaries. The local normal vector of the boundary can be calculated at each point, and the variation of this normal through space and with time can be assessed.…”

“…However, the signatures of the spacecraft transition between the lobe and the plasma sheet, which are the prime interest in this study, are generally observed as a change of plasma properties rather than magnetic field direction. Therefore, the Dunlop and Woodward (1999) method is not adopted in this study.…”

Cluster as a wave telescope – first results from the fluxgate magnetometer

“…These new instruments are, for example, the curlometer and the discontinuity analyzer (e.g. Dunlop et al, 1988Dunlop et al, , 1997Dunlop et al, , 1999 as well as the wave telescope (e.g. Musmann et al, 1974;Neubauer and Glassmeier, 1990;Lefeuvre, 1991, 1992;Stein et al, 1993;, 1996Pinçon and Motschmann, 1998), which has its roots in array signal analysis techniques developed for the interpretation of seismic array data (e.g.…”

A new technique for determining orientation and motion of a 2-D, non-planar magnetopause

“…play an important role in case of C2, affecting the results of the MVAB technique when applied on the central interval. We mention here that Dunlop and Woodward (1999), when studying, with synthetic data, how the local normal direction of a non-planar, ideal discontinuity, can be obtained by employing the planar MVAB method, showed that the errors are smaller when points from a short interval around the center of the structure are used. However, in case of a real event, a situation similar to that encountered by C2 on 24 June 2003 may occur.…”