Expansion of Magnetic Clouds for Different Solar Wind Conditions

DASSO, S.; DÉMOULIN, P.; GULISANO, A.M.; NAKWACKI, M.S.; CREMADES, H.; MANDRINI, C.H.; SCHMIEDER, B.; CID, C.; CERRATO, Y.; SAIZ, E.; RODRIGUEZ, L.; ZHUKOV, A.; ARAN, A.; MENVIELLE, M.; POEDTS, S.

Saint Malo

Congreso; Solar Wind 12 - 2009; 2009

From over two decades, several properties of magnetic clouds (MCs) have been recognized and distinguished from those associated with the quasi-stationary parkerian solar wind or with other non-cloud transient structures. In particular, in contrast with the parkerian solar wind, MCs have a significant expansion along the radial direction from the Sun. Several previous studies suggested that the increase of its size is self-similar. In a recent study, Demoulin & Dasso [A&A, in press] have shown theoretical reasons in favor of a nearly isotropic expansion for MCs, mainly driven by (a) the global decrease of the surrounding solar wind pressure with the distance to the Sun and (b) the stretching of its main axis (e.g., due to the feet of the flux rope still anchored to the Sun during its propagation); they also quantified a normalized expansion rate of MCs for typical solar wind conditions. The main aim of this work is to analyze MCs with significantly different expansion rates, focussing on the reasons for finding these differences. In particular we present the analysis of events which evolve in different environments, in a ?clean? solar wind or in a perturbed one (e.g., pushed by behind by another transient event). We quantify the expansion rates for different cases under dissimilar conditions of MCs evolution.