[11] In this section the ARs evolution (processes leading to formation of the d configurations, common features typical for ARs, and differences between ARs of different types) are analyzed. The results of the observations by ground-based instruments (in particular by cude-refractor Opton at High-Altitude Observatory of the Sternberg State Astronomical Institute (SSAI) with the Ha filter) and on board space stations obtained in the visible and far ultraviolet ranges of wavelengths and also in the X rays are used.
[12] Among the considered ARs one can find compact ARs which are d spots with a vast penumbra or d islands with dimensions of tens thousands of kilometers (AR McMath 11976, NOAA 5395, NOAA 5629, NOAA 5747, NOAA 6659, NOAA 7070) or extended ARs with a complicated structure of the magnetic field of the bgd configuration (AR NOAA 9077, NOAA 9393).
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| Figure 1 |
[14] On 11 March 1989, AR 5395 was located near the central meridian and presented a large monolithic formation of the N polarity surrounded from three sides by the south polarity field (Figure 1a). This AR was observed on the Sun during several rotations. Just in March it was formed as a large d configuration and demonstrated unusually high flare and geophysical activity. On 11 March its length was about 100''. Similarly, the AR 6659 presented a large monolithic island of the S polarity. Such large d islands are the most flare productive. This fact can be seen in Table 1. The numbers of the ARs presenting large d configurations are underline.
[15] The flare of the X15 importance was the most powerful X-ray flare in AR 5395. The most powerful proton event coincided with the 3B/X4.5 flare. In the scope of the data available for 19 active regions, there seems to be no correlation between the power of proton events and AR productivity in the X-ray range. For example, AR 5747 gave a powerful proton flare (40,000 pfu) as compared to the flare in AR 5395 (3500 pfu), but only 5 flares of the X class occurred in AR 5747, whereas 11 flares of the X class occurred in AR 5395. Table 1 shows that the proton flux can be associated to X-ray flares of both X and M classes.
[16] Sometimes emergence of a united compact system of d island is observed. Generation of isolated d groups probably is related to a formation of complicated magnetic tubes in the base of the convective zone. For example, the AR 7205 was born on the solar disk on 18 June 1992 at the western edge of a coronal hole and first 3 days consisted of ragged small spots. On 22 June the AR looked as a bipolar group with two leading spots of the S polarity and one following spot of the N polarity (Figure 1b). The leading and tail spots moved in the opposite directions from each other and were connected by a system of arch loops. However, already on 23 June one of the leading spots and the following spot united into a d spot [Van Driel-Gesztelyi et al., 1997]. A new bipole N8S13 which emerged on 23 June to 25 June fused to the main d spot (Figure 1b), and its leading part continued to grow until 26 June when the AR reached the west limb. The AR was the most flare productive on 25 and 26 June. It remained active also after the disappearance behind the limb.
[17] Satellite sunspots of the opposite polarity often emerge near a group of spots which have existed earlier. For example, the spot group observed in March 1991 as the AR 6555 existed for three more rotations. During the previous passage over the solar disc (the AR 6509) it presented a complicated system with a large spot of the N polarity. In March 1991 a rapid emergence of a new d group was observed near the old complex in the vicinity of the S1 spot (Figure 1c). During the next rotation (April 1991) only the area with short-lived and scattered pores of the N polarity was observed on the place of this AR [Kalman, 1997]. This AR was very active: a proton flare with the flux of 43,000 pfu occurred in it.
[18] Formation of a d configuration can happen as a result of a collision of two usual bipolar sunspot groups and mergence of a following spot of one group to the leading spot of the other group. This results in a formation of a d spot with the polarity reversed as compared to the polarity corresponding to the Hale-Nicolson law. Such process could be observed in the AR McMath 15314 which presented a huge complex consisting of five bipoles A, B, C, D, and E (Figure 1d). The region B appeared near the eastern limb as a large spot of the leading polarity. The C and D regions emerged close to each other with the difference of a few days within the B region. Figure 1d shows the AR on 27 May when the distance between CS and DN became minimum.
[19] As a result of the continued emergence of magnetic fluxes, there occurred a fusion of two spots of the leading polarity (BN-CN) and also mergence of the leading and the following spots of the inner groups (DN-CS) in one penumbra with formation of a d spot [Gaizauskas et al., 1994]. Uniting into one spot with the common penumbra of two spots of the opposite polarity belonging to two different dipoles, apparently, has been prepared by a reconnection of magnetic field lines under the photosphere or during the emergence of the new magnetic flux. During 5 days, insignificant flares were observed, and only on 28 May the 1B/X1 flare occurred when the umbra in the d spot began to decay accompanied by rapid motions at the photosphere level [Gaizauskas et al., 1994].
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