Abstract:
In the context of the Sun–Earth connection of coronal mass ejections and magnetic flux ropes (MFRs), we studied
the solar active region (AR) and the magnetic properties of magnetic cloud (MC) event during 2013 April 14–15.
We use in situ observations from the Advanced Composition Explorer and source AR measurements from the
Solar Dynamics Observatory. The MCs magnetic structure is reconstructed from the Grad–Shafranov method,
which reveals a northern component of the axial field with left handed helicity. The MC invariant axis is highly
inclined to the ecliptic plane pointing northward and is rotated by 117° with respect to the source region PIL. The
net axial flux and current in the MC are comparatively higher than from the source region. Linear force-free alpha
distribution (10−7–10−6 m−1) at the sigmoid leg matches the range of twist number in the MC of 1–2 au MFR. The
MFR is nonlinear force-free with decreasing twist from the axis (9 turns/au) toward the edge. Therefore, a Gold–
Hoyle (GH) configuration, assuming a constant twist, is more consistent with the MC structure than the Lundquist
configuration of increasing twist from the axis to boundary. As an indication of that, the GH configuration yields a
better fitting to the global trend of in situ magnetic field components, in terms of rms, than the Lundquist model.
These cylindrical configurations improved the MC fitting results when the effect of self-similar expansion of MFR
was considered. For such twisting behavior, this study suggests an alternative fitting procedure to better
characterize the MC magnetic structure and its source region links.
