Implications of Noncylindrical Flux Ropes for Magnetic Cloud Reconstruction Techniques and the Interpretation of Double Flux Rope Events 

Mathew Owens Submitted: 20120221 10:11
Magnetic clouds (MCs) are a subset of interplanetary coronal mass
ejections
(ICMEs) which exhibit signatures consistent with a magnetic flux rope
structure. Techniques
for reconstructing flux rope orientation from singlepoint in situ
observations typically assume
the flux rope is locally cylindrical, e.g., minimum variance analysis
(MVA) and forcefree
flux rope (FFFR) fitting. In this study, we outline a noncylindrical
magnetic flux rope
model, in which the flux rope radius and axial curvature can both vary
along the length of
the axis. This model is not necessarily intended to represent the
global structure of MCs,
but it can be used to quantify the error in MC reconstruction
resulting from the cylindrical
approximation. When the local flux rope axis is approximately
perpendicular to the heliocentric
radial direction, which is also the effective spacecraft trajectory
through a magnetic
cloud, the error in using cylindrical reconstruction methods is
relatively small (approx 10 deg). However,
as the local axis orientation becomes increasingly aligned with the
radial direction, the
spacecraft trajectory may pass close to the axis at two separate
locations. This results in a magnetic field time series which deviates
significantly from encounters with a forcefree
flux rope, and consequently the error in the axis orientation derived
from cylindrical reconstructions
can be as much as 90 deg. Such twoaxis encounters can result in an
apparent 'double flux rope' signature in the magnetic field time
series, sometimes observed in spacecraft
data. Analysing each axis encounter independently produces reasonably
accurate axis
orientations with MVA, but larger errors with FFFR fitting.
Authors: M.J. Owens, P. Demoulin, N.P. Savani, B. Lavraud, A. Ruffenach
Projects:

Publication Status: Published
Last Modified: 20120307 07:40




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