Kálmán, Béla (1997) Flow patterns around old sunspots and ﬂare activity. Astronomy and Astrophysics, 327 (2). pp. 779-785. ISSN 0004-6361
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, “ω-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 “Ω-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 180◦. 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 (δ-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.
|Subjects:||Q Science / természettudomány > QB Astronomy, Astrophysics / csillagászat, asztrofizika|
|Depositing User:||Mr András Holl|
|Date Deposited:||06 Apr 2010 05:27|
|Last Modified:||05 Sep 2012 10:16|
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