The role of magnetic handedness in magnetic cloud propagation

Abstract

We investigate the propagation of magnetic clouds (MCs) through the inner heliosphere using 2.5-D ideal magnetohydrodynamic (MHD) simulations. A numerical solution is obtained on a spherical grid, either in a meridional plane or in an equatorial plane, by using a Roe-type approximate Riemann solver in the frame of a finite volume approach. The structured background solar wind is simulated for a solar activity minimum phase. In the frame of MC propagation, special emphasis is placed on the role of the initial magnetic handedness of the MC's force-free magnetic field because this parameter strongly influences the efficiency of magnetic reconnection between the MC's magnetic field and the interplanetary magnetic field. Magnetic clouds with an axis oriented perpendicular to the equatorial plane develop into an elliptic shape, and the ellipse drifts into azimuthal direction. A new feature seen in our simulations is an additional tilt of the ellipse with respect to the direction of propagation as a direct consequence of magnetic reconnection. During propagation in a meridional plane, the initial circular cross section develops a concave-outward shape. Depending on the initial handedness, the cloud's magnetic field may reconnect along its backside flanks to the ambient interplanetary magnetic field (IMF), thereby losing magnetic flux to the IMF. Such a process in combination with a structured ambient solar wind has never been analyzed in detail before. Furthermore, we address the topics of force-free magnetic field conservation and the development of equatorward flows ahead of a concave-outward shaped MC. Detailed profiles are presented for the radial evolution of magnetoplasma and geometrical parameters. The principal features seen in our MHD simulations are in good agreement with in-situ measurements performed by spacecraft. The 2.5-D studies presented here may serve as a basis under more simple geometrical conditions to understand more complicated effects seen in 3-D simulations.