Flow patterns around old sunspots and flare activity
Received 7 March 1997 / Accepted 12 May 1997
New magnetic flux emerges significantly more probably in already existing solar active regions. Based on the the Debrecen Observatory photographic observations, several active regions are collected, where at least one large, X-class flare was recorded, and emergence of new activity, birth and quick motion of new umbrae was observed in the vicinity of old spots, the new activity emerged in the center of the old active region.
Newly emerging magnetic flux in older sunspot groups can be distinguished by its quicker and generally westward proper motions. Umbrae of the new activity do not coalesce with older umbrae of the same polarity, but both elastic and inelastic collisions between them can be observed. Spots of the emerging new activity can flow around old unipolar spots (presumably shallower structures, " -loops") westward, like a hydrodynamic flow around a cylinder, forming a wake behind it. Collision of different polarities in the wake can lead to large flares. The presence of old spots disturbs the normal emergence of the new activity, so motions of the new spots are distorted by the flow, the new emerging " -loop" can be stuck between the umbrae of the old, tight dipole, the orientation of the new dipole can be distorted by as much as . The general direction of the flow around the old spots seems to depend on the latitude, the angle between the motion axis and the E-W direction grows with the latitude.
The intensive flare activity seems to be connected strongly with the newly emerging magnetic flux; interacting of differently oriented dipoles and the difference of the orientation of the emerging new dipole from the ordinary Hale-Nicholson orientation is also significant. Simply large gradients of magnetic fields ( -configuration) are not enough, dynamical processes (emergence of new flux, shearing or colliding motions of umbrae of different magnetic polarity) must also be present for large flares.
Key words: Sun: activity Sun: flares sunspots
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© European Southern Observatory (ESO) 1997
Online publication: April 6, 1998