Magnetic helicity in the solar corona

MANDRINI, C.H.

Buneos Aires

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

Asociación Argentina de Astronomía

Conferencia invitada Magnetic helicity is a measurement of the magnetic field deformation with respect to its minimum energy state. Solar coronal observations show that an enormous quantity of phenomena occur in non-potential magnetic configurations, while satellite data indicate the existence of twisted magnetic flux tubes in the interplanetary medium. In the last decades several observations and measurements of the so-called ``current helicity´´ (which is related to magnetic helicity) lead us to the determination of hemispheric chiriality rules. From a theoretical point of view, magnetic helicity is one of the few quantities that is preserved in scales shorter than the global diffusion time (which is several orders of magnitude longer than the typical temporal evolution of the solar magnetic field). Therefore, the study of magnetic helicity allows us to link phenomena that take place in very different regimes. Through its analysis, we can follow the evolution of the field from its emergence from the subphotospheric regions to the interplanetary medium, where it is observed in situ as a magnetic cloud after being ejected from the Sun. After briefly mentioning the principal properties of magnetic helicity, we will review the works relevant to the determination of the hemispheric chiriality rules. Then, we will discuss the results of the most recent papers that evaluate the relative importance of the different magnetic helicity sources in the corona, e.g. photospheric plasma motions or the twist of flux tubes originated at the base of the convective zone. Finally, we will outline the perspectives of this new research area.