Mass Motions Under the Influence of the Magnetic Field in Solar Active Regions

Statistics – Computation

Scientific paper

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Arch Filament Systems, Active Region, Chromosphere, Cloud Model

Scientific paper

We have studied the development of active region arch structures in Hα and mass motions associated with them. Our emphasis was on the spatial structure and the temporal evolution of the velocity. We reconstructed the velocity vector along the arch filaments and computed models for the material flow. A large developing active region (Mc Math No 16315) was observed for six days from September 25 to September 30 1979. The observations were obtained with a Halle Hα filter (0.5 Passband) mounted on the 50 cm "Tourelle" refractor of the Pic-du-Midi Observatory. On the first day of our observations the active region consisted of only two well developed spots, while on the sixth day it had many large spots and its structure was quite complex. We also used observations of an arch filament system (AFS) in NOAA region 4819 made on June 22, 1987 covering a time interval of 15 m 27 sec. These observations were obtained with the Multichannel Double Pass Spectograph (MSDP) mounted on the 50 cm "Tourelle" refractor of the Pic-du-Midi observatory. The MSDP provides 10 simultaneous intensity images of the same region, 0.256 Angstrem apart in the Hα line. We developed a method for the computation of the line-of-sight velocity from photographs at Hα+- 0.5 Angstrem, under the assumption of Becker's cloud model and resonable assumptions about the Doppler width and optical depth of the arches. For the MSDP data we reconstructed line profiles and monochromatic images and we measured Doppler velocities. Furthemore, using Becker's cloud model, we derived physical parameters and in particular the line of sight velocity. from the line of sight component of the velocity we computed the horizontal and the vertical components along the arch filaments. For this purpose we reconstructed the three dimensional shape of the loops, assuming that they were symmetric with respect to the apex. Finally we have studied the motion of an inviscid isothermal plasma under the influence of gravity in an translational symmetric magnetic field. We considered a time varying flow along a steady loop. The solutions of the MHD eauations were compared with the observations of the material flow in the arch filaments.

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