Morphological model for quadrupolar δ sunspots

Abstract:

Sunspot with umbrae of opposite polarity within a single common penumbra are called δ-spot group (Kunzel, 1960). It has been well known that major flares almost always occur in active region with δ-configuration. Hence, to investigate the formation and evolution of δ-configuration is a key in understanding the major flare activities. However, for the case of δ-spot, emerging flux regions (EFRs) combine intricately to each other. Therefore it is so difficult to decipher the relations between multiple EFRs. To clearly follow the development of the ARs, we should select the ARs which can be observed from the initial emerging stage.

Emergence and magnetic evolution of solar active regions (ARs) of βγδ-type, which are known to be highly flare active (Sammis 2000), were studied with the SOHO/MDI data in the solar cycle 23. 31 ARs, which can be seen from the birth phase, were selected as unbiased samples of our study.

From our analysis, we found that successive birth of two emerging flux regions, spatially separated to each other in east-west direction as a series, forming a quadrupolar magnetic configuration, is a typical way of initial development of βγδ regions. The δ-configuration was formed by following polarity of western EFR with preceding polarity of eastern EFR.

We found 11ARs of quadrupolar type among the sampled 31 ARs.

In this work, we propose a plausible model for the quadrupolar type δ-spots as a simple magnetic tube of helical structure, which have downward knot in the mid portion of the flux tube. In nine cases out of 11, the characteristics of the magnetic helicity signs, i.e. the signs of twist and writhe, are consistent with our model.