Polynomial reconstruction of the magnetic field observed by multiple
spacecraft with integrated velocity determination
Abstract
Recently a polynomial reconstruction technique has been developed for
reconstructing the magnetic field in the vicinity of multiple
spacecraft, and has been applied to events observed by the
Magnetospheric Multiscale (MMS) mission. Whereas previously the magnetic
field was reconstructed using spacecraft data from a single time, here
we extend the method to allow input over a span of time. This extension
increases the amount of input data to the model, improving the
reconstruction results, and allows the velocity of the magnetic
structure to be calculated. The effect of this modification, as well as
many other options, is explored by comparing reconstructed fields to
those of a three-dimensional particle in cell simulation of magnetic
reconnection, using virtual spacecraft data as input. We often find best
results using multiple-time input, a moderate amount of smoothing of the
input data, and a model with a reduced set of parameters based on the
ordering that the maximum, intermediate, and minimum values of the
gradient of the vector magnetic field are well separated. When
spacecraft input data are temporally smoothed, reconstructions are
representative of spatially smoothed fields. Two MMS events are
reconstructed. The first of these was late in the mission when it was
not possible to use the current density for MMS4 because of its
instrument failure. The second shows a rotational discontinuity without
an X or O line. In both cases, the reconstructions yield a visual
representation of the magnetic structure that is consistent with earlier
studies.