Dynamical evolution of a magnetic cloud from the Sun to 5.4 AU

<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>
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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.
Fil:Nakwacki, M.S. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.
Fil:Dasso, S. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.
Fil:Mandrini, C.H. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.
Fil:Gulisano, A.M. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.
Astron. Astrophys. 2011;535
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
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
Interplanetary spacecraft
Magnetic fields
Magnetic flux
Planetary surface analysis
Solar system
Solar wind
Nivel de accesibilidad
Acceso abierto
Biblioteca Digital (UBA-FCEN)
Universidad Nacional de Buenos Aires. Facultad de Ciencias Exactas y Naturales
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