Evolution of Interplanetary Coronal Mass Ejections for different solar wind conditions

DASSO, S.; GULISANO A.M.; DEMOULIN, P.; RUIZ M.E.; MARSCH, E.

Ubatuba São Paulo - Brazil

Conferencia; The Influence of Solar Variability on Geophysical and Heliospheric Phenomena, International Living With a Star Workshop; 2009

International Living With a Star (NASA, USA) and INPE (Brazil)

Transient structures in the heliosphere have significantly differentproperties than those typically found in the stationary solar wind.In particular, from over two decades several properties ofInterplanetary Coronal Mass Ejections (ICMEs) have been recognizedand distinguished from those associated with the parkerian solar windor from other non-ICMEs transient structures. In particular,in contrast with the parkerian solar wind, ICMEs have a significantexpansion along the radial direction from the Sun.Magnetic clouds (MCs) form a sub-set of ICMEs, presenting to anheliospheric observer a large and coherent magnetic field, a lowproton temperature, and a higher magnetic pressure than the sourrondingsolar wind. Several previous studies have shown that the increaseof the MC size is self-similar. Recently, Demoulin \& Dasso [A\&A, in press]have shown theoretical reasons in favor of a nearly isotropic expansion,mainly driven by (a) the global decrease of the surroundingsolar wind pressure with the distance to the Sun and (b) the stretchingof their main axes (e.g., caused because the feet of the flux rope canbe anchored to the Sun during their propagation). These authors alsoquantified a normalized expansion rate for clouds for typical solar wind conditions.The main aim of this work is to analyze MCs with significantlydifferent expansion rates, focussing on the reasons for finding thesedifferences. In particular we discuss the characteristics of eventsthat evolve in different environments, in a 'clean' solar wind orin a perturbed one (e.g., pushed by behind by another transient event),and quantify their expansion rates.