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Astron. Astrophys. 329, 1138-1144 (1998)

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4. Summary

The activity complex studied here represents a basic structural element of the eleven year solar activity cycle. It occupied a substantial fraction of the solar surface. Its evolution exhibited a progressive increase in the number and size of its active regions, reaching a phase of peak activity during two rotations in June and July 1982. After this the magnetic field became greatly simplified over this entire area, with the lines of force opening into the interplanetary space, forming in its final stages a large coronal hole.

From the identification of pivot lines and pivot points for the rotation of the main boundary of the activity complex, we conclude that its subphotospheric source of magnetic flux rotated as a rigid body for at least four rotations prior to the phase of maximum activity. During this final most energetic phase, either the connection with the underlying source of flux had been severed, or the source itself had changed. On energetic grounds, a considerable emergence of new flux probably took place during the numerous strong flares that occurred within the complex before its destruction.

The complete "lifecycle" of this activity complex underscores the fundamental importance of large-scale subsurface processes for the generation, emergence, transformation and dissipation of the global magnetic field. It offers further insight into the relative rates at which activity builds up and then rapidly dissipates. Since a similar lifecycle was observed in detail during the following cycle, an anologous development of stellar activity complexes might be expected, given similar temporal and spatial organization of activity on other solar-like stars.

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© European Southern Observatory (ESO) 1998

Online publication: December 16, 1997