A new model-independent method to quantify magnetic helicity in interplanetary clouds

DASSO, S.; GULISANO, A.M.; MANDRINI, C.H.; DÉMOULIN, P.

Mérida

Workshop; Sun-Earth connection physics: The geoimpact of CMEs, CIRs and ordinary solar wind; 2004

Los Alamos National Observatory

Magnetic clouds are extended and magnetized plasma structures that travel from theSun toward the outer heliosphere, carrying an important amount of magnetic helicity. Since the helicity is practically conserved in the solar atmosphere and the heliosphere, it is a useful quantity to compare the physical properties of magnetic clouds to those of their solar source regions. In this work we describe a method that, assuming a cylindrical geometry for the magnetic cloud structures, allows us to calculate their helicity (per unit length) content directly from the observed magnetic field values. We apply the method to a set of 20 magnetic clouds observed by theWIND spacecraft. To test its reliability we compare our results with the helicity computed using a linear force-free field model under cylindrical geometry (i.e. Lundquist?s solution).