Expansion of magnetic clouds in the outer heliosphere

<div class="autor_fcen" id="4119">Gulisano, A.M.</div>; Démoulin, P.; <div class="autor_fcen" id="2288">Dasso, S.</div>; Rodriguez, L.
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Context. A large amount of magnetized plasma is frequently ejected from the Sun as coronal mass ejections (CMEs). Some of these ejections are detected in the solar wind as magnetic clouds (MCs) that have flux rope signatures. Aims. Magnetic clouds are structures that typically expand in the inner heliosphere. We derive the expansion properties of MCs in the outer heliosphere from one to five astronomical units to compare them with those in the inner heliosphere. Methods. We analyze MCs observed by the Ulysses spacecraft using in situ magnetic field and plasma measurements. The MC boundaries are defined in the MC frame after defining the MC axis with a minimum variance method applied only to the flux rope structure. As in the inner heliosphere, a large fraction of the velocity profile within MCs is close to a linear function of time. This is indicative of a self-similar expansion and a MC size that locally follows a power-law of the solar distance with an exponent called ζ. We derive the value of ζ from the in situ velocity data. Results. We analyze separately the non-perturbed MCs (cases showing a linear velocity profile almost for the full event), and perturbed MCs (cases showing a strongly distorted velocity profile). We find that non-perturbed MCs expand with a similar non-dimensional expansion rate (ζ = 1.05 ± 0.34), i.e. slightly faster than at the solar distance and in the inner heliosphere (ζ = 0.91 ± 0.23). The subset of perturbed MCs expands, as in the inner heliosphere, at a significantly lower rate and with a larger dispersion (ζ = 0.28 ± 0.52) as expected from the temporal evolution found in numerical simulations. This local measure of the expansion also agrees with the distribution with distance of MC size, mean magnetic field, and plasma parameters. The MCs interacting with a strong field region, e.g. another MC, have the most variable expansion rate (ranging from compression to over-expansion). © 2012 ESO.
Fil:Gulisano, A.M. 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.
Astron. Astrophys. 2012;543
Interplanetary medium
Magnetic fields
Magnetohydrodynamics (MHD)
Solar wind
Sun: coronal mass ejections (CMEs)
Astronomical units
Coronal mass ejection
Expansion properties
Expansion rate
Flux ropes
Interplanetary medium
Linear functions
Linear velocity
Magnetic clouds
Magnetized plasmas
Mean magnetic field
Minimum variance
Outer heliosphere
Plasma measurement
Plasma parameter
Strong field
Sun: coronal mass ejection
Temporal evolution
Ulysses spacecraft
Velocity profiles
Magnetic fields
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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