Magnetic Flux and Helicity of Magnetic Clouds

JANVIER, M.; DASSO, S.; DEMOULIN, P.

SOLAR PHYSICS

SPRINGER

Lugar: Berlin; Año: 2016 vol. 291 p. 531 - 557

0038-0938

Magnetic clouds (MCs) are formed by flux ropes (FRs) launched from the Sun aspart of coronal mass ejections (CMEs). They carry away a large amount of magnetic flux andhelicity. The main aim of this study is to quantify these amounts from in situ measurementsof MCs at 1 AU. The fit of these data by a local FR model provides the axial magnetic fieldstrength, the radius, the magnetic flux, and the helicity per unit length along the FR axis. Weshow that these quantities are statistically independent of the position along the FR axis. Wethen derive the generic shape and length of the FR axis from two sets of MCs. These resultsimprove the estimation of magnetic helicity. Next, we evaluate the total magnetic flux andhelicity that cross the sphere of radius of 1 AU, centred at the Sun, per year and duringsolar cycle. We also include in the study two sets of small FRs that do not have all the typicalcharacteristics of MCs. While small FRs are at least ten times more numerous than MCs, themagnetic flux and helicity are dominated by the contribution from the larger MCs. In oneyear they carry away the magnetic flux of about 25 large active regions and the magnetichelicity of 200 of them. MCs carry away an amount of unsigned magnetic helicity similarto the amount estimated for the solar dynamo and that measured in emerging active regions.