4 Motions of P6-F4 on 14 July

Many observations show that during a large flare the position and shape of a sunspot can be obviously perturbed. Proper motion calculations are important for understanding the relation between spots dynamics and flares. Because of the limits of ground-based observations, such as seeing, intermission, precision, and instrumental resolution, it is difficult to precisely measure the proper motions. Using the YOHKOH white-light data, Anwar et al. (1993) find a rapid sunspot displacement for a white-light flare (X1.5). The approximate velocity is as high as 2.0 km s^-1. The major flare of 14 July is also a white-light flare (X5.7, 10:10 UT) with two ribbons just outside of F4 and P6. For this reason, we study the proper motions on 14 July. The proper motion measurements are based on the method described by Liu & Zhang (2001) and the positions are translated into Carrington coordinates. Figure 4 displays the projections of the trajectories into the Carrington system with a time interval of 96 minutes. In this figure, the arrowheads and black points represent their positions with time. It is obvious that there are two different periods: (a) before 08:00 UT, we observe relative shear motions between P6 and F4 and (b) after 08:00 UT, we find irregular motions between them.

Based in Fig. 4, the velocities are calculated and shown in Fig. 5. F4 is represented by squares while P6 by diamonds. The dashed lines indicate the time of the flare maximum (10:24 UT). The spots do not show as high a rate as that found by Anwar et al. (1993). Obviously, about two hours before the flare, F4 reaches its highest velocity (0.73 km s^-1) while P6 slows down to its lowest velocity (0.03 km s^-1). Around the flare maximum, both of them move at a normal rate. Therefore, it seems that two hours before the major flare, the $\delta$-configuration is disturbed. Note that, after the flare maximum, P6 slows down again to a very low velocity for its decay. P6 disappears completely late on the next day. There are no X-class flares in the super-active region after 14 July. We also calculate the proper motions of P6 and F4 for 12 hours after the flare, but find no abnormality.

  

Table 1: List of magnetograms in active region 9077. Column $h_{\rm c}$ gives the helicity sign of spot F4.

$$\begin{tabular}{llllllll} \hline\hline No. & Time & Date &$... ...$-$ & {\it {18}}. & 00:52 & 15 &$+$\\ \hline \end{tabular}$$