A model for accelerated density enhancements emerging from coronal streamers in Large-Angle and Spectrometric Coronagraph observations

Abstract

Recent Large-Angle and Spectrometric Coronagraph (LASCO) white light observations, ranging between 2R_S and 32R_S, trace accelerated density enhancements in the vicinity of the Sun which can be detected as enhancement in the intensity of the Thomson scattered light. One interpretation of these observed density enhancements is that they indicate moving plasmoids in the corona. Such plasmoids are accelerated away from the Sun by a Lorentz force due to the radial solar magnetic field. A model of accelerated plasmoids is presented which includes this magnetic acceleration, the Sun's gravitational attraction, and the aerodynamic drag acting on the plasmoid as it interacts with the solar wind. With reasonable choices of physical parameters the model produces velocity-height profiles close to the observed ones. Profiles for external initial Alfvén velocities v_Ae0=80, 350, and 450 km/s (external initial magnetic field B_e0=0.04, 0.16, and 0.21 Gauss) at r₀=5R_S approximately match the lower, the middle, and the upper range of the observed velocity profiles, respectively. Choices for the ratio of the initial plasmoid number density n_i0 and the initial solar wind number density n_e0 of 2<n_i0/n_e0<12 guarantee a slowly decreasing relative intensity enhancement in the range of observations. Only moderate line of sight intensity enhancements can be caused by a small and dense plasmoid.