Modeling Non-Force-Free and Deformed Flux Ropes in Titan’s Ionosphere

Martin, Carley and Arridge, Chris and Badman, Sarah and Billett, Daniel and Barratt, C. J. (2020) Modeling Non-Force-Free and Deformed Flux Ropes in Titan’s Ionosphere. Journal of Geophysical Research: Space Physics, 125 (4): e2019JA027. ISSN 2169-9402

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Abstract

Previous work at Titan presented a set of 85 flux ropes detected during Cassini flybys of Titan from 2005 to 2017. In that study a force‐free model was used to determine the radii and axial magnetic field of the flux ropes. In this work we apply non‐force‐free models. The non‐force‐free model shows an improvement in the number of flux ropes that can be fitted with a model, along with improved uncertainties and χ2 values. A number of asymmetries and features in the magnetometer data cannot be reproduced by either model; therefore, we deform the force‐free model to show that small deformations can replicate these features. One such deformation is to use an elliptical cross section, which replicates a plateau in magnetic field strength along with asymmetries on either side of the center of the flux ropes. Additionally, we explore the properties of bending a flux rope, where we find that minimum variance analysis becomes increasingly degenerate with bending, along with a slight bend causing the switching of the axial field direction from intermediate to maximum variance direction. We conclude that the flux ropes at Titan show aspects of developing flux ropes, compared to other planetary bodies, which exhibit more agreement to the force‐free assumptions of mature flux ropes.