Authors: <div class="autor_fcen" id="6067">Nakwacki, M.S.</div>; <div class="autor_fcen" id="2288">Dasso, S.</div>; Démoulin, P.; <div class="autor_fcen" id="5317">Mandrini, C.H.</div>; <div class="autor_fcen" id="4119">Gulisano, A.M.</div>
Publication Date: 2011.
Context. Significant quantities of magnetized plasma are transported from the Sun to the interstellar medium via interplanetary coronal mass ejections (ICMEs). Magnetic clouds (MCs) are a particular subset of ICMEs, forming large-scale magnetic flux ropes. Their evolution in the solar wind is complex and mainly determined by their own magnetic forces and the interaction with the surrounding solar wind. Aims. Magnetic clouds are strongly affected by the surrounding environment as they evolve in the solar wind. We study expansion of MCs, its consequent decrease in magnetic field intensity and mass density, and the possible evolution of the so-called global ideal-MHD invariants. Methods. In this work we analyze the evolution of a particular MC (observed in March 1998) using in situ observations made by two spacecraft approximately aligned with the Sun, the first one at 1 AU from the Sun and the second one at 5.4 AU. We describe the magnetic configuration of the MC using different models and compute relevant global quantities (magnetic fluxes, helicity, and energy) at both heliodistances. We also tracked this structure back to the Sun, to find out its solar source. Results. We find that the flux rope is significantly distorted at 5.4 AU. From the observed decay of magnetic field and mass density, we quantify how anisotropic is the expansion and the consequent deformation of the flux rope in favor of a cross section with an aspect ratio at 5.4 AU of ≈ 1.6 (larger in the direction perpendicular to the radial direction from the Sun). We quantify the ideal-MHD invariants and magnetic energy at both locations, and find that invariants are almost conserved, while the magnetic energy decays as expected with the expansion rate found. Conclusions. The use of MHD invariants to link structures at the Sun and the interplanetary medium is supported by the results of this multi-spacecraft study. We also conclude that the local dimensionless expansion rate, which is computed from the velocity profile observed by a single-spacecraft, is very accurate for predicting the evolution of flux ropes in the solar wind. © 2011 ESO.
Author affiliation: Nakwacki, M.S. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.
Author affiliation: Dasso, S. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.
Author affiliation: Mandrini, C.H. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.
Author affiliation: Gulisano, A.M. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.
Keywords: Magnetic fields; Magnetohydrodynamics (MHD); Solar wind; Sun: coronal mass ejections (CMEs); Sun: heliosphere; Sun: magnetic topology; Cross section; Dynamical evolution; Expansion rate; Flux ropes; Global quantities; Helicities; In-situ observations; Interplanetary coronal mass ejections; Interplanetary medium; Interstellar mediums; Link structure; Magnetic clouds; Magnetic configuration; Magnetic energies; Magnetic flux ropes; Magnetic force; Magnetic-field intensity; Magnetized plasmas; Magnetohydrodynamics (MHD); Mass densities; Radial direction; Solar source; Sun: coronal mass ejections (CMEs); Surrounding environment; Velocity profiles; Aspect ratio; Clouds; Expansion; Interplanetary spacecraft; Magnetic fields; Magnetic flux; Magnetoplasma; Planetary surface analysis; Solar system; Solar wind; Wind; Magnetohydrodynamics.
Repository: Biblioteca Digital (UBA-FCEN). Universidad Nacional de Buenos Aires. Facultad de Ciencias Exactas y Naturales