The Magnetic Helicity Budget of Solar Active Regions: from the Photosphere to Magnetic Clouds

MANDRINI, C.H.

Córdoba

Workshop; 11th UN/ESA Workshop on Basic Space Sciences; 2002

United Nations - European Space Agency

Conferencia invitada Magnetic helicity is one of the few solar physical magnitudes which is conserved even in non-ideal magnetohydrodynamics on time scales shorter than the global diffusion time. Magnetic helicity is generated in the solar interior, buoyant flux tubes transport it through the convective zone and inject it into the solar corona, where photospheric large scale (differential rotation) and small scale motions also contribute. Increasing observational evidence indicates that magnetic helicity of a given dominant sign is injected in each solar hemisphere and that this sign does not change during the solar cycle. Being this so, magnetic helicity would accumulate incensantly unless the Sun finds a way the get rid of it. Coronal mass ejections (CMEs) are the phenomena through which magnetic helicity can be ejected from the Sun into the interplanetary medium. Twisted magnetic plasma structures, of which magnetic clouds are a subset, are frequently observed in the near Earth environment. Based on observations and modelling of two well studied CME productive active regions (ARs), we evaluate the relative importance of the different sources of coronal magnetic helicity in these ARs. We compute the helicity ejected in CMEs associating every one of them to an interplanetary magnetic cloud. For this computation we use observational averaged values for the cloud parameters, together with standard cloud models. We find that the ejected magnetic helicity can only come from the twist (subphotospheric origin) inherent to the flux tube forming the AR. This kind of studies is aimed to characterize the CME ejection mechanism and to improve our forescasting ability of CMEs.