On 18 January 1989, solar activity in the active region AR 5312 enhanced obviously from 05:00 to 09:52UT, and ordinary flares appeared one after another (NOAA 1989). The active region was monitored with the multi-band optical instrument (see Table 4 (click here)) at Yunnan Observatory.
A series of H filtergrams of the active region was obtained with the vacuum solar telescope (Instrument 1, Wu et al. 1990) from 03:30 to 08:18UT on 18 January (see Table 3 (click here) and Fig. 1 (click here)). The data of scanning photographs and synchronous H filtergrams of the white light flare (S30 W65) were also obtained with the two-dimension multi-band spectroheliograph SSHG (Instrument 2, Xuan & Lin 1993) in three wave bands (H, H and H) during five different time intervals from 07:00UT to 07:52UT (Xuan et al. 1991). In the meantime, fine structure observations (see Figs. 2 (click here) and 3 (click here)) of sunspots in the region were made with the solar photosphere telescope (Instrument 3, see Table 4 (click here)) of Yunnan Observatory several days before and after 18 January. The longitudinal components of the magnetic field during the same time interval were also obtained with the solar magnetic field telescope (Ai & Hu 1986) at the Huairou Station of Beijing Observatory (see Fig. 3 (click here)).
The lifetime of the WLF and sizes of the kernels before maximum (see Table 5 (click here)) were obtained by comparing the spectral data with H filtergrams. The spectral films were measured with a PDS microdensitometer and processed on a VAX-8350 computer. The changes of the spectral line profiles in the WLF kernels are shown in Fig. 4 (click here) (see Sect. 3.3).