Dynamics of the slow solar wind

Seminar given by Victor Reville, IRAP (Salle Lyot, Belin)

Abstract : The solar wind, in particular the slow component, harbors many dynamical structures. Density perturbations have been observed with coronagraphs and heliospheric imagers for more than 20 years. These so-called « blobs » seem to be released periodically from the low corona, in association with downflows that could be the signature of magnetic reconnection. In situ measurements have been able to associate (at least) part of these density structures to flux ropes, i.e. helical structures connected to the Sun. In this talk, I will review recent efforts to explain the origin of these structures and their relation to helmet streamers and the heliospheric current sheet (HCS). Using 2.5D and 3D simulations, I will show how helmet streamers are naturally unstable and lead, in a two-step process, to the release of flux ropes and density perturbations. The periodicity recovered in the simulations are consistent with observations and involve the ideal tearing mode at high Lundquist numbers. Comparing 3D MHD simulations with data of Parker Solar Probe and Solar Orbiter, I will show that a lot of the observed dynamics is consistent with numerous flux ropes born at the tip of helmet streamers and propagating close to the HCS. Finally, I will discuss the 3D structures of these flux ropes and the possible relation between the onset of the streamers instability and the thermal structure of the corona, controlled by the separatrice and quasi-separatrice network.