Features of the Expansion of flux ropes in the outer heliosphere

GULISANO A.M.; DEMOULIN, P.; DASSO, S.; RODRIGUEZ L.

mar del plata

Conferencia; 55ª Reunión Anual de la Asociación Argentina de Astronomía; 2012

asociación argentina de astronomía

Frecuently coronal mass ejections (CMEs) are ejected from the Sun and detected in the solarwind. They show flux rope features conforming magnetic clouds (MCs), which are magnetizedplasma structures. It is well known that MCs are typically in expansion during their travel fromthe Sun to 1 Astronomical Unit (AU). In order to compare this features with the ones in theouter heliosphere, we analyse the expasion properties of MCs from 1.5 to 5.4 AU. We study a setof MCs observed by Ulysses mission from july 1992 to july 2002, analysing ?in situ? magnetic andplasma measured data. We apply the normalized minimum variance technique (MV) to the magneticmeasurements to get the orientation of the magnetic structure and find the MC local frame and theMCs boundaries from the components of the magnetic field inside the cloud using this frame. We findthat a large fraction of MCs presents a linear trend in the radial velocity profile as a function of time,which implies a self-similiar expansion of the structure with an evolution of the MC size that locallyfollows a power-law (exponent ) evolution with heliodistance. As we did in the inner heliospherein a recent previous work, we analized separately the MCs showing a linear velocity profile that wecalled non-perturbed, and the ones showing a distorted velocity profile that we called perturbed. Wefind that the non-perturbed MCs expand with a non-dimensional expansion rate  = 1.05 ± 0.34,a similar value to the value found in the inner heliosphere. The perturbed MCs expands, as in theinner heliosphere, at a significantly lower rate and with a larger dispersion ( = 0.28 ± 0.52) as canbe expected from numerical simulations in another works.