Numerical simulations of the evolution of magnetic field kinks in the solar wind
Résumé
We investigate, via Magnetohydrodynamic (MHD) numerical simulations, the evolution of large amplitude Alfvénic fluctuations that include a component parallel to the background magnetic field leading to kinked magnetic field lines. When the amplitude of those kinks is sufficiently large, the total magnetic field folds back on itself leading to a local inversion of its polarity. Local magnetic field polarity inversions, also known as "switchbacks", are common features of the Alfvénic solar wind and have been observed in a wide range of heliocentric distances (from 0.3 AU all the way out to a few AU), and most recently by Parker Solar Probe during its first two encounters. The stability and evolution of switchbacks in the expanding solar wind has not yet been studied in detail. In this work we compare the dynamical evolution of exact nonlinear Alfvénic solutions to the MHD system, characterized by constant total magnetic pressure, with the evolution of unbalanced structures, and we determine under which conditions "switchbacks" can propagate in the solar wind, their stability and lifetime.