Magnetic helicity in interplanetary structures of solar origin

DASSO, S.; MANDRINI, C.H.; DÉMOULIN, P.

Buenos Aires

Congreso; 45 Reunión Anual de Asociación Argentina de Astronomía; 2002

Asociación Argentina de Astronomía

Interplanetary manifestations of transient coronal mass ejections (so called ICMEs) form helical structures of magnetic flux that travel through the solar wind from the Sun toward the outer heliosphere. The global magnetic helicity (MH) contained in these huge structures, whose typical length when pass near Earth is of the order of an astronomical unit, plays a very important role in the understanding of the solar-terrestrial relationship. Moreover, the study of MH is crucial in order to link solar active regions with their corresponding interplanetary flux tubes. MH is one of the few global quantities conserved even under non-ideal MHD. In spite of its importance do not yet exist exhaustive studies that estimate the content of MH in ICMEs. In spite of ICMEs are structures out of equilibrium, generally ICMEs are modeled using three different MHD models with cylindrical geometry: linear force-free field, constant twist angle, and non force-free model with constant current. In this work, we derive analytically the expressions to calculate the MH for every of the three models mentioned before, and also present numerical results for a hot flux tube observed by the spacecraft Wind on October 24-25, 1995. We have fitted the set of free parameters for every model, finding that the derived MHs are very similar. Thus, our results support that the MH in ICMEs is a well-determined quantity what do not depend of the assumed model, being very valuable in order to get insight of the link between solar and interplanetary phenomena.