Suspension Of A Dense Plasma Blob On A Vertical Magnetic Field Line

A long standing problem with in Prominence investigations relates to the presence of density strands stretching from the main body of prominences toward the solar surface. How can such dense plasma blobs be supported against gravity and not fall down with the free fall velocity. Together with Duncan Mackay I set up a series of experiments where we used an initially hydro static atmosphere with a clear transition region. In the coronal part of the model a cold and dense plasma blob was dumped into the hydro static background plasma. Through this we had an initially horizontal constant magnetic field. When the magnetic field is above a lower limit the density blob will start falling down due to the increased effect from gravity on the blob relative the surrounding coronal plasma. The presence of the magnetic field prevents the traditional Rayleigh-Taylor instability to develop. The blob falls the pressure below it enhanced as the plasma is compressed. This pushes the magnetic field out. Eventually the back reaction of the increasing tension force reverses the expansion of the field lines and an inverse force blobs up enough pressure to stop the fall of the density blob and reverse it's motion. The effect is that the blob oscillated around an equilibrium position. During this process the density contrast between the blob and the coronal plasma decreases and it becomes less visible with time.
The experiments show that when the density enhance meant is sufficient small, then they may have life times that a significantly longer than the free fall time of the coronal plasma.
The experiments, until now, have been simple in the sense that they have not properly taking into account the effect of heat conduction and optical thin radiation. The effect of these physical quantities are at present being investigated and will be reported in a following paper.

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Last updated 03.02.01