How Well Can the Observed Flux Ropes in the Solar Wind be Fitted by a Uniform-twist Flux Rope Model?

Abstract:

In the solar wind, flux ropes, e.g., magnetic clouds (MCs), are a frequently observational phenomenon. Their magnetic field configuration or the way that the field lines wind around the flux rope axis is one of the most important information to understand the formation and evolution of the observed flux ropes. Most MCs are believed to be in the force-free state, and widely modeled by the Lundquist force-free solution, in which the twist of the field line increases from zero at the axis to infinity at the boundary. However, Lundquist solution is not the only form of a force-free magnetic field. Some studies based on suprathermal electron observations and models have shown that MCs may carry magnetic field lines more likely to be uniformly twisted. The nonlinear force-free field extrapolation of solar magnetic field also suggests that the field lines of a flux rope twist limitedly. In this study, we have developed a velocity-modified uniform-twist force-free flux rope model, and fit observed MCs with this model. By using this approach, we test how well the observed MCs can be fitted into a uniform-twist flux rope. Some interesting results will be given in this presentation.