The dynamical behavior of Magnetic Clouds: From 0.3 to 5.4 astronomical units

GULISANO ADRIANA MARÍA; SERGIO DASSO; PASCAL DÉMOULIN

Paris

Congreso; IAUS300, Nature of Prominences and their role in Space Weather; 2013

IAUS

Transient magnetized plasma structures expelled from the Sun can produce strong distortions in the terrestrial environment. In particular,  a subset of these structures called Magnetic Clouds (MCs) present an enhanced, smooth magnetic field with a coherent rotation when observed in situ by a probe. Magnetic Clouds are expected to expand during their travel from the Sun to the outer heliospheredue to the decrease of the solar wind pressure with heliodistance. Typical spatial scales of MCs allow to study them within the magnetohydrodynamic (MHD) framework. Then, using an MHD theoretical model which considers self-similar expansion, together with magnetic and plasma data from a sample of MCs observed by Helios 1-2 andUlysses, we analyze  the evolution of the MC size for solar distances from 0.3 to 5.4 AU.We compared the expansion behavior observed at the inner heliophere (from $0.3$ to $1$ AU) with that found at the outer heliosphere (from $1.5$ to $5.4$ AU). A significant subset of the studied events presents a linear trend inthe radial bulk velocity profile, which can be associated with a self-similar expansion of the structure, with a size evolving locallyas a power law (with exponent $zeta$) of heliodistance. We analyze separately events presenting this linear velocity profiles (we named them as ´non perturbed´) from the ones that do not present this characteristic (we named them ´perturbed´). For the outer heliosphere, we found that the exponent $zeta$ is significantly different for ´perturbed´ and ´non perturbed´ MCs, finding $zeta_{no-perturbed}=1.05pm 0.34$ and $zeta_{perturbed}=0.28pm 0.52$. A similar value was found in a previous work for the inner heliosphere. These results were consistent with expectations given from some previous numerical simulations.