Magnetic Flux and Helicity of Magnetic Clouds

TL;DR

This study quantifies magnetic flux and helicity of magnetic clouds at 1 AU, revealing their statistical independence along flux ropes and their significant contribution to solar magnetic flux and helicity transfer.

Contribution

It provides new statistical estimates of magnetic flux and helicity in magnetic clouds, improving understanding of their structure and role in solar magnetic flux transfer.

Findings

Magnetic flux and helicity are statistically independent of position along flux ropes.

Large magnetic clouds dominate the magnetic flux and helicity contributions.

Magnetic clouds carry away flux and helicity comparable to solar dynamo estimates.

Abstract

Magnetic clouds (MCs) are formed by flux ropes (FRs) launched from the Sun as part of coronal mass ejections (CMEs). They carry away an important amount of magnetic flux and helicity. The main aim of this study is to quantify these quantities from insitu measurements of MCs at 1 AU. The fit of these data by a local FR model provides the axial magnetic field strength, the radius, the magnetic flux and the helicity per unit length along the FR axis. We show that these quantities are statistically independent of the position along the FR axis. We then derive the generic shape and length of the FR axis from two sets of MCs. These results improve the estimation of magnetic helicity. Next, we evaluate the total magnetic flux and helicity crossing the sphere of radius of 1 AU, centered at the Sun, per year and during a solar cycle. We also include in the study two sets of small FRs which do not have all the typical characteristics of MCs. While small FRs are at least ten times more numerous than MCs, the magnetic flux and helicity are dominated by the contribution from the larger MCs. They carry in one year the magnetic flux of about 25 large active regions and the magnetic helicity of 200 of them. MCs carry away an amount of unsigned magnetic helicity comparable to the one estimated for the solar dynamo and the one measured in emerging active regions.