CONICET | Buscador de Institutos y Recursos Humanos

Magnetic helicity (MH) quantifies various aspects of a given magnetic structure, such as the twist, kink, and the number of knotts between magnetic field lines, the linking between magnetic flux tubes, the shear in layers of magnetic flux, etc. MH is practically conserved in the solar atmosphere and in the heliosphere. The relation between the MH generated in the Sun and that ejected into the interplanetary medium is not yet well known. Interplanetary magnetic clouds (MCs) are huge objects that travel from the Sun toward the external heliosphere carrying an important amount of MH. Despite being expanding systems, in situ observations of their magnetic field have been frequently modelled using several different magnetohydrostatic solutions. At present, it is not at all evident which model gives the best representation of their magnetic structure. Interest has grown on both the solar physics and the interplanetary communities to study the relation between the helicity generated in the Sun and ejected into the interplanetary medium. However, detailed studies of the magnetic helicity in MCs do not yet exist. In this work we analyse the helicity content of the magnetic cloud observed by the spacecraft Wind on October 18-19, 1995; we use three different models with cylindrical symmetry (two of them are force free and the third one has constant current). We compute the free parameters for each of the three models from observations and, from the fitted values, we compute the MH and compare the results. These multi-approaches allow us to quantify the range of MH contained in the MC. We found that even if the distribution of the twist inside the MC is very different in every model, the MH is practically independent of the model. We also conclude that, due to the sensitivity of the helicity content with the radius of the cloud, it is essential to use an appropriate method in order to determine, without ambiguity, the orientation of the flux tube.

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