Causes and consequences of magnetic cloud expansion

Context. A magnetic cloud (MC) is a magnetic flux rope in the solar wind (SW), which, at 1 AU, is observed ∼2-5 days after its expulsion from the Sun. The associated solar eruption is observed as a coronal mass ejection (CME).Aims. Both the in situ observations of plasma velocity distribution and th...

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Autor principal:	Dasso, Sergio Ricardo
Publicado:	2009
Materias:	interplanetary medium Sun: coronal mass ejections (CMEs) Sun: magnetic fields Boundary pressure Coronal mass ejection Cylindrical flux ropes Expansion rate Flux ropes Force free fields In-situ observations Magnetic clouds Magnetic energies Magnetic flux ropes Magnetic helicity Plasma velocity Radial distributions Radial expansions Radial velocity Self-similar Solar eruption Astrophysics Boundary layer flow Energy conservation Expansion Fluid dynamics Magnetic fields Magnetic flux Magnetic structure Magnetohydrodynamics Ordinary differential equations Pressure gradient Solar wind Sun Velocity Velocity distribution Solar energy
Acceso en línea:	https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_00046361_v498_n2_p551_Demoulin http://hdl.handle.net/20.500.12110/paper_00046361_v498_n2_p551_Demoulin
Aporte de:	Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) de Universidad de Buenos Aires

id	paper:paper_00046361_v498_n2_p551_Demoulin
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spelling	paper:paper_00046361_v498_n2_p551_Demoulin2023-06-08T14:27:49Z Causes and consequences of magnetic cloud expansion Dasso, Sergio Ricardo interplanetary medium Sun: coronal mass ejections (CMEs) Sun: magnetic fields Boundary pressure Coronal mass ejection Cylindrical flux ropes Expansion rate Flux ropes Force free fields In-situ observations interplanetary medium Magnetic clouds Magnetic energies Magnetic flux ropes Magnetic helicity Plasma velocity Radial distributions Radial expansions Radial velocity Self-similar Solar eruption Sun: coronal mass ejections (CMEs) Sun: magnetic fields Astrophysics Boundary layer flow Energy conservation Expansion Fluid dynamics Magnetic fields Magnetic flux Magnetic structure Magnetohydrodynamics Ordinary differential equations Pressure gradient Solar wind Sun Velocity Velocity distribution Solar energy Context. A magnetic cloud (MC) is a magnetic flux rope in the solar wind (SW), which, at 1 AU, is observed ∼2-5 days after its expulsion from the Sun. The associated solar eruption is observed as a coronal mass ejection (CME).Aims. Both the in situ observations of plasma velocity distribution and the increase in their size with solar distance demonstrate that MCs are strongly expanding structures. The aim of this work is to find the main causes of this expansion and to derive a model to explain the plasma velocity profiles typically observed inside MCs.Methods. We model the flux rope evolution as a series of force-free field states with two extreme limits: (a) ideal magneto-hydrodynamics (MHD) and (b) minimization of the magnetic energy with conserved magnetic helicity. We consider cylindrical flux ropes to reduce the problem to the integration of ordinary differential equations. This allows us to explore a wide variety of magnetic fields at a broad range of distances to the Sun.Results. We demonstrate that the rapid decrease in the total SW pressure with solar distance is the main driver of the flux-rope radial expansion. Other effects, such as the internal over-pressure, the radial distribution, and the amount of twist within the flux rope have a much weaker influence on the expansion. We demonstrate that any force-free flux rope will have a self-similar expansion if its total boundary pressure evolves as the inverse of its length to the fourth power. With the total pressure gradient observed in the SW, the radial expansion of flux ropes is close to self-similar with a nearly linear radial velocity profile across the flux rope, as observed. Moreover, we show that the expansion rate is proportional to the radius and to the global velocity away from the Sun.Conclusions. The simple and universal law found for the radial expansion of flux ropes in the SW predicts the typical size, magnetic structure, and radial velocity of MCs at various solar distances. © 2009 ESO. Fil:Dasso, S. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. 2009 https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_00046361_v498_n2_p551_Demoulin http://hdl.handle.net/20.500.12110/paper_00046361_v498_n2_p551_Demoulin
institution	Universidad de Buenos Aires
institution_str	I-28
repository_str	R-134
collection	Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA)
topic	interplanetary medium Sun: coronal mass ejections (CMEs) Sun: magnetic fields Boundary pressure Coronal mass ejection Cylindrical flux ropes Expansion rate Flux ropes Force free fields In-situ observations interplanetary medium Magnetic clouds Magnetic energies Magnetic flux ropes Magnetic helicity Plasma velocity Radial distributions Radial expansions Radial velocity Self-similar Solar eruption Sun: coronal mass ejections (CMEs) Sun: magnetic fields Astrophysics Boundary layer flow Energy conservation Expansion Fluid dynamics Magnetic fields Magnetic flux Magnetic structure Magnetohydrodynamics Ordinary differential equations Pressure gradient Solar wind Sun Velocity Velocity distribution Solar energy
spellingShingle	interplanetary medium Sun: coronal mass ejections (CMEs) Sun: magnetic fields Boundary pressure Coronal mass ejection Cylindrical flux ropes Expansion rate Flux ropes Force free fields In-situ observations interplanetary medium Magnetic clouds Magnetic energies Magnetic flux ropes Magnetic helicity Plasma velocity Radial distributions Radial expansions Radial velocity Self-similar Solar eruption Sun: coronal mass ejections (CMEs) Sun: magnetic fields Astrophysics Boundary layer flow Energy conservation Expansion Fluid dynamics Magnetic fields Magnetic flux Magnetic structure Magnetohydrodynamics Ordinary differential equations Pressure gradient Solar wind Sun Velocity Velocity distribution Solar energy Dasso, Sergio Ricardo Causes and consequences of magnetic cloud expansion
topic_facet	interplanetary medium Sun: coronal mass ejections (CMEs) Sun: magnetic fields Boundary pressure Coronal mass ejection Cylindrical flux ropes Expansion rate Flux ropes Force free fields In-situ observations interplanetary medium Magnetic clouds Magnetic energies Magnetic flux ropes Magnetic helicity Plasma velocity Radial distributions Radial expansions Radial velocity Self-similar Solar eruption Sun: coronal mass ejections (CMEs) Sun: magnetic fields Astrophysics Boundary layer flow Energy conservation Expansion Fluid dynamics Magnetic fields Magnetic flux Magnetic structure Magnetohydrodynamics Ordinary differential equations Pressure gradient Solar wind Sun Velocity Velocity distribution Solar energy
description	Context. A magnetic cloud (MC) is a magnetic flux rope in the solar wind (SW), which, at 1 AU, is observed ∼2-5 days after its expulsion from the Sun. The associated solar eruption is observed as a coronal mass ejection (CME).Aims. Both the in situ observations of plasma velocity distribution and the increase in their size with solar distance demonstrate that MCs are strongly expanding structures. The aim of this work is to find the main causes of this expansion and to derive a model to explain the plasma velocity profiles typically observed inside MCs.Methods. We model the flux rope evolution as a series of force-free field states with two extreme limits: (a) ideal magneto-hydrodynamics (MHD) and (b) minimization of the magnetic energy with conserved magnetic helicity. We consider cylindrical flux ropes to reduce the problem to the integration of ordinary differential equations. This allows us to explore a wide variety of magnetic fields at a broad range of distances to the Sun.Results. We demonstrate that the rapid decrease in the total SW pressure with solar distance is the main driver of the flux-rope radial expansion. Other effects, such as the internal over-pressure, the radial distribution, and the amount of twist within the flux rope have a much weaker influence on the expansion. We demonstrate that any force-free flux rope will have a self-similar expansion if its total boundary pressure evolves as the inverse of its length to the fourth power. With the total pressure gradient observed in the SW, the radial expansion of flux ropes is close to self-similar with a nearly linear radial velocity profile across the flux rope, as observed. Moreover, we show that the expansion rate is proportional to the radius and to the global velocity away from the Sun.Conclusions. The simple and universal law found for the radial expansion of flux ropes in the SW predicts the typical size, magnetic structure, and radial velocity of MCs at various solar distances. © 2009 ESO.
author	Dasso, Sergio Ricardo
author_facet	Dasso, Sergio Ricardo
author_sort	Dasso, Sergio Ricardo
title	Causes and consequences of magnetic cloud expansion
title_short	Causes and consequences of magnetic cloud expansion
title_full	Causes and consequences of magnetic cloud expansion
title_fullStr	Causes and consequences of magnetic cloud expansion
title_full_unstemmed	Causes and consequences of magnetic cloud expansion
title_sort	causes and consequences of magnetic cloud expansion
publishDate	2009
url	https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_00046361_v498_n2_p551_Demoulin http://hdl.handle.net/20.500.12110/paper_00046361_v498_n2_p551_Demoulin
work_keys_str_mv	AT dassosergioricardo causesandconsequencesofmagneticcloudexpansion
_version_	1768546470589366272

Causes and consequences of magnetic cloud expansion

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