Expansion rate of Magnetic Clouds beyond Earth

Magnetic Clouds (MCs) are interplanetary manifestations of transient structures erupted from the Sun. They are formed by strong helical magnetic field lines, and their configuration evolve accordingly to their interaction with the surrounding plasma. Due to the decay of the solar wind pressure for increasing heliodistance, and because their magnetic configuration remains as an entity during their evolution, MCs are objects in global expansion. When the MC is not perturbed by fast streams or other interplanetary transients, its expansion rate is expected to be in agreement with the rate of decay of total solar wind pressure, as it was recently confirmed by observations at the ecliptic plane in the inner heliosphere and near Earth. In this work we present results of the local expansion of MCs observed at heliodistances between one and five AUs. In particular, we compute the dimensionless expansion rate (ζ [Démoulin et al., Solar Physics, 2008]) using the MC bulk velocity profile in-situ observed by Ulysses. We analyze the dependence of ζ with heliodistance, MC size and other MC properties. As it was done previously for the inner heliosphere, we find now that when the MC is not perturbed by the environment (and thus it shows a linear bulk velocity profile) ζ is in a very good agreement with the expected global expansion.