3 Formation of $\delta$-spot P6-F4

AR 9077 was in a highly sheared magnetic configuration classified as $\beta\gamma\delta$. Here, we follow the nomenclature in Liu & Zhang (2001) to describe the spots. Figure 1 shows some images illustrating the evolution of the global spot group. The main spots are P1, P2, and F1 on 11 July. P1 and F1 are in a large $\delta$-structure when the active region first emerges from the solar east limb. Many small pores, including F4 and P6, are growing and coalescing in their penumbrae as evident in the white-light movie. On 11 July, F4 is in the south of the penumbra of P1, so that they are also in a local $\delta$-configuration, although their areas and fluxes are not balanced.

Figure 1: TRACE white-light (5000 Å) images of the evolution of sunspot group AR 9077. The main spots are P1, P2 and F1 on July 11, 2000. Spots F4 and P6 moved together to form a $\delta$-spot directly from different penumbrae on July 13. "P'' means preceding (positive), and "F'' following (negative). FOV: $3'\times 2.3'$. (An MPEG movie can be obtained from the URL http://sun.bao.ac.cn/staff/lyu/spot.mpe, or seen directly on-line at http://sun.bao.ac.cn/staff/lyu/gifmovie/gifmovie.html)

Figure 2: Vector magnetogram of HSOS superimposed on the corresponding white-light image from TRACE. The white contours represent positive longitudinal magnetic fields, black contours represent negative fields. Arrows are in the direction of the transverse fields with a length proportional to the field strength. The box in the left frame outlines the $\delta$-spot P6-F4. The right frame is an enlargement with transverse fields superimposed. The magnetic contour levels are 600, 1200, 2000, and 3000 G. The FOV of left frame is $2.1\hbox {$^\prime $ }\times 2.1'$ and $20\hbox {$^{\prime \prime }$ }\times 20\hbox {$^{\prime \prime }$ }$ for the right frame.

It is interesting that F4 is "dropped" by the fast west-moving P1 and met by P6 to form a new small $\delta$-spot early on 13 July. The $\delta$-spot P6-F4 grows quickly in size and separates from the old spot, developing a new penumbra. Since the formation of $\delta$-spot P6-F4 is related to the old delta structure, it can be classified as a special case of those listed in Sect. 1. On 14 July, a major 3B/X5.7 flare erupts at 10:10 UT. About two hours before, P6-F4 begin an obvious and quick separation with P6 sliding to the north of F4. The next day, P6 disappears and F4 coalesces with the penumbra of a new spot P9 which is indicated by an arrow in Fig. 1.

Figure 2 outlines the location of P6-F4 in the active region on 14 July and gives an enlargement of this region with vector magnetic field overlaying the white-light image. Detailed magnetic field evolution is shown in Fig. 3. The $\delta$-configuration of P6-F4 exists from 13-15 July. The major flare seems to be the accelerator of its separation. Three boxes shown in Fig. 3 indicate the $\delta$-configurations formed by F4 with P1, P6 and P9, respectively. This implies that F4 is a very dynamic magnetic feature worth deep research.

Figure 3: A sequence of vector magnetograms observed from 11 to 17 July. FOV: $3'\times 2.3'$. White (black) patches are positive (negative) longitudinal magnetic fields. The contour levels of the longitudinal field are 160, 420, 680, and 1070 G. White contours represent positive polarities and black contours negative polarities. The bars indicate transverse fields with a length proportional to the field strength. Note, that the three boxes are at the locations of the $\delta$-configurations formed by F4 with P1, P6, and P9, respectively.