LINKING CORONAL TO HELIOSPHERIC MAGNETIC HELICITY: A NEW MODEL-INDEPENDENT TECHNIQUE TO COMPUTE HELICITY IN MAGNETIC CLOUDS

摘要

Magnetic clouds (MCs) are a subset of interplanetary coronal mass ejections (ICMEs), which carry a significant amount of large scale magnetic helicity (MH) away from the solar corona as they travel to the external helio-sphere. From a theoretical point of view, it is expected that MH be preserved in the solar corona and the helio-sphere. In particular, it will be preserved in MCs during their evolution through the interplanetary medium. Thus, MH plays a key role to link the magnetic properties of MCs with their solar active region (AR) sources, helping us to improve the knowledge of the ejection mechanisms in the corona. MH studies permit also to restrict the various models proposed to represent the structure of clouds. We present here a new method to compute the MH in clouds, which provides values for the helicity per unit length along the flux tube axis using the observed interplanetary magnetic field. The method only assumes that the cloud section is circular. We apply this method to two MCs, one of the biggest and one of the smallest ever observed, and compare our results with the helicity ejected from their respective solar sources.