Study of an expanding magnetic cloud

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

La Plata, Buenos Aires, Argentina

Congreso; 48 Reunión de la Asociación Argentina de Astronomía; 2005

Magnetic Clouds (MCs) transport into the interplanetarymedium the magnetic  ux and helicity released in coronal mass ejectionsby the Sun. At 1 AU from the Sun, MCs are generally modelled as static ux ropes. However, the velocity profile of some MCs presents signaturesof expansion. We analise here the magnetic structure of an expandingmagnetic cloud observed by Wind spacecraft. We consider a dynamicalmodel, based on a self-similar behaviour for the cloud´s radial velocity. Weassume a free expansion for the cloud, and a cylindrical linear force freefield (i.e., the Lundquist´s field) as the initial condition for its magneticconfiguration. We derive theoretical expressions for the magnetic  uxacross a surface perpendicular to the cloud axis, for the magnetic helicityand magnetic energy per unit length along the tube using the self-similarmodel. Finally, we compute these magnitudes with the fitted parameters.