Magnetic cloud models with bent and oblate cross-section boundaries

Démoulin, P.; <div class="autor_fcen" id="2288">Dasso, S.</div>
Publication Year
Published version
Context. Magnetic clouds (MCs) are formed by magnetic flux ropes that are ejected from the Sun as coronal mass ejections. These structures generally have low plasma beta and travel through the interplanetary medium interacting with the surrounding solar wind. Thus, the dynamical evolution of the internal magnetic structure of a MC is a consequence of both the conditions of its environment and of its own dynamical laws, which are mainly dominated by magnetic forces.Aims. With in-situ observations the magnetic field is only measured along the trajectory of the spacecraft across the MC. Therefore, a magnetic model is needed to reconstruct the magnetic configuration of the encountered MC. The main aim of the present work is to extend the widely used cylindrical model to arbitrary cross-section shapes.Methods. The flux rope boundary is parametrized to account for a broad range of shapes. Then, the internal structure of the flux rope is computed by expressing the magnetic field as a series of modes of a linear force-free field.Results. We analyze the magnetic field profile along straight cuts through the flux rope, in order to simulate the spacecraft crossing through a MC. We find that the magnetic field orientation is only weakly affected by the shape of the MC boundary. Therefore, the MC axis can approximately be found by the typical methods previously used (e.g., minimum variance). The boundary shape affects the magnetic field strength most. The measurement of how much the field strength peaks along the crossing provides an estimation of the aspect ratio of the flux-rope cross-section. The asymmetry of the field strength between the front and the back of the MC, after correcting for the time evolution (i.e., its aging during the observation of the MC), provides an estimation of the cross-section global bending. A flat or/and bent cross-section requires a large anisotropy of the total pressure imposed at the MC boundary by the surrounding medium.Conclusions. The new theoretical model developed here relaxes the cylindrical symmetry hypothesis. It is designed to estimate the cross-section shape of the flux rope using the in-situ data of one spacecraft. This allows a more accurate determination of the global quantities, such as magnetic fluxes and helicity. These quantities are especially important for both linking an observed MC to its solar source and for understanding the corresponding evolution. © 2009 ESO.
Fil:Dasso, S. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.
Astron. Astrophys. 2009;507(2):969-980
Interplanetary medium
Sun: coronal mass ejections (CMEs)
Sun: magnetic fields
Arbitrary cross section
Boundary shapes
Coronal mass ejection
Cylindrical models
Cylindrical symmetry
Dynamical evolution
Field strengths
Flux ropes
Global quantities
In-situ data
In-situ observations
Internal structure
Interplanetary medium
Large anisotropy
Magnetic clouds
Magnetic configuration
Magnetic field orientations
Magnetic field profile
Magnetic field strengths
Magnetic flux ropes
Magnetic models
Minimum variance
Solar source
Sun: coronal mass ejection
Sun: magnetic field
Theoretical models
Time evolutions
Total pressure
Aspect ratio
Boundary layer flow
Interplanetary spacecraft
Magnetic fields
Magnetic flux
Magnetic structure
Planetary surface analysis
Solar wind
Semiconductor counters
Access level
Open access
Biblioteca Digital (UBA-FCEN)
Universidad Nacional de Buenos Aires. Facultad de Ciencias Exactas y Naturales
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