Writhed Analytical Magnetic Flux Rope Model. Issue 12 (30th November 2022)

• Record Type: Journal Article
• Authors: Weiss, A. J.; Nieves‐Chinchilla, T.; Möstl, C.; Reiss, M. A.; Amerstorfer, T.; Bailey, R. L.
• Is Part Of: Journal of geophysical research. Volume 127:Issue 12(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-11-30
• Subjects: flux rope modeling -- ICMEs -- flux ropes; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2022JA030898
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: Observations of magnetic clouds, within interplanetary coronal mass ejections (ICMEs), are often well described by flux rope models. Most of these assume either a cylindrical or toroidal geometry. In some cases, these models are also capable of accounting for non‐axisymmetric cross‐sections but they generally all assume axial invariance. It can be expected that any ICME, and its flux rope, will be deformed along its axis due to influences such as the solar wind. In this work, we aim to develop a writhed analytical magnetic flux rope model which would allow us to analytically describe a flux rope structure with varying curvature and torsion so that we are no longer constrained to a cylindrical or toroidal geometry. In this first iteration of our model we will solely focus on a circular cross‐section of constant size. We describe our flux rope geometry in terms of a parametrized flux rope axis and a parallel transport frame. We derive expressions for the axial and poloidal magnetic field components under the assumption that the total axial magnetic flux is conserved. We find an entire class of possible solutions, which differ by the choice of integration constants, and present the results for a specific example. In general, we find that the twist of the magnetic field locally changes when the geometry deviates from a cylinder or torus. This new approach also allows us to generate completely new types of in situ magnetic field profiles which strongly deviate from those generated by cylindrical or toroidal models. Key Points: We develop an analytical model that can be used to describe writhed flux ropes by describing the flux rope axis as a general space curve We show how this model can be implemented numerically in terms of quadratic splines and configured for an arbitrary twist distribution We find that the field lines resulting from our model have lower twist per unit length than would be expected from a toroidal approximation