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Session 1 - Chromosphere, Corona, Flares.
Display session, Friday, June 27
Ballroom B, Chair: Charles Kankelborg
We have investigated how a solar equilibrium plasma with smooth magnetic field configuration evolves when thermal properties of the whole atmosphere change or when field line footpoints are slowly moved. We found that critical values of control parameters exist over which the plasma equilibrium changes its topology from a smooth configuration to form a very thin current sheet. Our studies are based on two-dimensional MHD equilibrium solutions with quadrupolar field geometry that mimic four sunspots with different polarities. Depending on the mass distribution as a function of magnetic flux, different current sheet topologies can result. If the plasma mass density is higher in the inner flux tubes, the plasma pressure gradient pushes out the field lines in each bipolar region so that a current sheet of a finite length forms at the region where the field lines from each bipolar region come into contact when the plasma temperature is above a critical value. The current sheet in this case grows in height from the bottom boundary. This type of current sheet configuration can also be achieved by shearing field line footpoints because an increase in field line footpoint shear will expand the field lines just like in the case of an increase in the plasma heat content. If resistivity is applied to this current sheet configuration, magnetic reconnection changes the field topology into one with an X-point, which may occur during certain solar flares. However, if the mass density is higher in the outer tubes than in the inner ones, a different current sheet configuration is formed with a sharp-pointed end of the current sheet hanging at a distance above the bottom boundary as the plasma temperature is uniformly lowered. If resistivity is considered, a "new" Kippenhahn-Schlüter type of field configuration with a magnetic island hanging in the solar atmosphere can result from magnetic reconnection. This may be similar to certain types of solar prominences.
Program listing for Friday