Abstract
Abstract. Recent multi-spacecraft studies of solar wind discontinuity crossings using the timing (boundary plane triangulation) method gave boundary parameter estimates that are significantly different from those of the well-established single-spacecraft minimum variance analysis (MVA) technique. A large survey of directional discontinuities in Cluster data turned out to be particularly inconsistent in the sense that multi-point timing analyses did not identify any rotational discontinuities (RDs) whereas the MVA results of the individual spacecraft suggested that RDs form the majority of events. To make multi-spacecraft studies of discontinuity crossings more conclusive, the present report addresses the accuracy of the timing approach to boundary parameter estimation. Our error analysis is based on the reciprocal vector formalism and takes into account uncertainties both in crossing times and in the spacecraft positions. A rigorous error estimation scheme is presented for the general case of correlated crossing time errors and arbitrary spacecraft configurations. Crossing time error covariances are determined through cross correlation analyses of the residuals. The principal influence of the spacecraft array geometry on the accuracy of the timing method is illustrated using error formulas for the simplified case of mutually uncorrelated and identical errors at different spacecraft. The full error analysis procedure is demonstrated for a solar wind discontinuity as observed by the Cluster FGM instrument.
Highlights
The analysis of discontinuities in space plasmas has received a lot of attention since the beginning of the space age
A large survey of directional discontinuities in Cluster data turned out to be inconsistent in the sense that multi-point timing analyses did not identify any rotational discontinuities (RDs) whereas the minimum variance analysis (MVA) results of the individual spacecraft suggested that RDs form the majority of events
The principle variants of the timing approach to boundary analysis discussed in Sect. 3 require slightly different parameter estimation and error analysis strategies
Summary
The analysis of discontinuities in space plasmas has received a lot of attention since the beginning of the space age. Applications of the MVA technique to solar wind discontinuities were recently challenged in a comprehensive study based on data from ESA’s Cluster satellites (Knetter et al, 2004; Knetter, 2005). Such multi-spacecraft missions offer an independent road to boundary parameter estimation through a crossing time analysis that effectively yields a boundary plane triangulation technique or, in brief, the socalled timing method. The present paper addresses one of the main team objectives, namely, the construction of a rigorous error analysis scheme for the timing method.
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