The optical characteristics of the white light flare on 18 January of 1989 are summarized as the following.
1. Shapes: The WLF consists of 7 kernels in patch-like shape (circular, elliptical or cashew-like form), with sizes from to cm2.
2. Lifetimes: The lifetimes of the WLF kernels vary from several minutes to more than 40 minutes. The kernels appeared simultaneously 2 to 3 minutes after the H flare, and their maxima occurred before the first maximum (such as kernel 1) and 1 to 2 minutes before the second maximum of the H flare. They disappeared slowly before the disappearance of the H flare.
3. Motions: The direction and scale of material motion in the kernels are different.
4. Source points: The initial bright points of the kernels were between umbra and penumbra, in penumbra fibrils, in the area between penumbra fibrils and the photosphere, on the photosphere or on the light bridge.
5. Precursors: There were plages in the locations where the WLF kernels lay, and the plages were relatively stationary. Some small flares had appeared at the sites of the plages, and the lifetimes of the plages are longer than that of the WLF. The chromospheric fibrils near the kernels bent toward the active region, forming an orderly pattern (the development and disappearance of the kernels were basically along this direction). Large chromospheric quiet filaments and small active ones were activated. However, WLFs and their continuum emissions were only observed in places where small filaments were activated and then rapidly disappeared, and some small flares occurred and new flux emerged. In other areas, only ordinary flares were observed.
6. Magnetic field: The magnetic configuration of the photosphere in the active region is in -structure. The kernels (except for kernel 3) were lying on or near the changing magnetic neutral lines, and the small gradient of longitudinal field may be constrained by the small transverse field on the photosphere.
7. Class: The central reversal and line width of the spectral line
profiles of the WLF kernels exhibit both temporal and spatial properties, and
the WLF is of mixed class one with characteristics of both class I and II.
The authors are thankful to Luan Ti, Wang Hongzhao, Zhang Xiaoyu and other fellows in the spectral research group of Yunnan Observatory for their cooperation in observation. We fully appreciated the help of the PDS group of Purple Mountain Observatory and the Vax computer group of Yunnan Observatory in our data processing. We should also be obliged to Huairou station of BeiJing Observatory for providing the magnetic field data. This work was supported by the grant 94A087M of the Science Foundation of Yunnan Province and the work of XMG and JL were also partly supported by the grants 19333041 and 19333042, respectively, of the National Scientific Foundation of China.