Changes in magnetic field topology and current intensity during a filament eruption

Using images taken by the BBSO telescope and the TRACE satellite, we have examined a prominence eruption occurred in AR 9077 at the west limb of the Sun, on July 19th, 2000. We have followed the morphological evolution of the prominence several hours before its activation and during the eruption phase. Assuming that the filament may be approximated as a cylindrical flux tube initially anchored in the solar surface and taking into account the different inclinations of the filament axis compared to the solar surface, we have determined several geometrical and physical parameters. The results of this analysis indicate that, after an initial phase of constant velocity eruption, the filament seems to oscillate and then it starts to rise again towards higher levels till when the plasma is ejected. Moreover, it has been possible to determine a decrease in the twist of the prominence magnetic field and to infer the behaviors of the axial electric current and of the filament total mass over time. The implications of these results in the framework of a screw-instability is briefly discussed....