The effects of expansion and turbulence on the interplanetary evolution of a magnetic cloud

Abstract

Coronal mass ejections (CMEs) represent the most extreme solar products, showing complex and dynamic structures when detected in situ. They are often preceded by a shock and carry a magnetic cloud organised as a flux rope, surrounded and permeated by turbulent fluctuations, and whose radial size expands during propagation. We investigate the internal dynamics of the 2D section of a cylindrical flux rope propagating at constant velocity in the spherically expanding solar wind, employing the expanding box model, which allows for high spatial resolution. Our setting is simplified, with uniform and non-magnetised solar wind, to which we superpose turbulent fluctuations. We find that the spherically expanding geometry alone perturbs the flux rope equilibrium, producing a radial head-tail velocity profile and a radial size increase. The ratio between the expansion and Alfvén timescales, associated respectively to propagation and internal crossing time, controls the resistance to transverse stretching and the increase of the flux rope radial extent; the plasma beta controls the overall size of the structure. Turbulent fluctuations mainly affect the flux rope transverse structure, spreading its axial field at distances comparable to its size; on the contrary, dynamics along the radial direction remains coherent and the increase in radial size is still consistently observed. We validate our results by comparison with statistical observations and dimensionless estimates, such as the expansion parameter and the radial size scaling exponent, suggesting that the ratio between internal and propagation timescales might help in better classifying different kinds of radial expansions for flux ropes.

19 pages, 16 figures, accepted in A&A

References in corpus (15)

• Global and local expansion of magnetic clouds in the inner heliosphere
• Self-Similarity of ICME Flux Ropes: Observations by Radially Aligned Spacecraft in the Inner Heliosphere
• Evolution of turbulence in the expanding solar wind, a numerical study
• Diamagnetic and Expansion Effects on the Observable Properties of the Slow Solar Wind in a Coronal Streamer
• Heliospheric Evolution of Magnetic Clouds
• Energetics of solar coronal mass ejections
• Inconsistencies Between Local and Global Measures of CME Radial Expansion as Revealed by Spacecraft Conjunctions
• Turbulent cascade and energy transfer rate in a solar coronal mass ejection
• Turbulent Heating between 0.2 and 1 au: A Numerical Study
• Properties of the Sheath Regions of Coronal Mass Ejections with or without Shocks from STEREO in situ Observations near 1 AU
• Spacetime Hall-MHD turbulence at sub-ion scales: structures or waves?
• Turbulence Properties of Interplanetary Coronal Mass Ejections in the Inner Heliosphere: Dependence on Proton Beta and Flux Rope Structure
• Turbulence and particle energization in twisted flux ropes in solar-wind conditions
• Evolution of the Radial Size and Expansion of Coronal Mass Ejections Investigated by Combining Remote and In-Situ Observations
• Turbulence, intermittency and cross-scale energy transfer in an interplanetary coronal mass ejection