Paper detail

Comparison of magnetic properties in a magnetic cloud and its solar source on April 11-14 2013

In the context of 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 April 14-15, 2013. We use in-situ observations from the Advanced Composition Explorer and source AR measurements from the Solar Dynamic 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 $117^o$ 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 non-linear force-free with decreasing twist from the axis (9 turns/AU) towards the edge. Therefore 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 to that, the GH configuration yields 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 considered the effect of self-similar expansion of MFR. For such twisting behaviour, this study suggests an alternative fitting procedure to better characterise the MC magnetic structure and its source region links.