Plasmoid formation and acceleration in the solar streamer belt

The dynamical behavior of a configuration consisting of a plane fluid wake flowing in a current sheet embedded in a plasma sheet that is denser than i ts surroundings is discussed. This configuration is a useful model for a nu mber of structures of astrophysical interest, such as solar coronal streame rs, cometary tails, the Earth's magnetotail and Galactic center nonthermal filaments. In this paper, the results are applied to the study of the forma tion and initial motion of the plasma density enhancements observed by the Large-Angle Spectrometric Coronagraph (LASCO) instrument onboard the Solar and Heliospheric Observatory (SOHO) spacecraft. It is found that beyond the helmet cusp of a coronal streamer, the magnetized wake configuration is re sistively unstable, that a traveling magnetic island develops at the center of the streamer, and that density enhancements occur within the magnetic i slands. As the massive magnetic island travels outward, both its speed and width increase. The island passively traces the acceleration of the inner p art of the wake. The values of the acceleration and density contrasts are i n good agreement with LASCO observations.