第22太阳活动周软X射线耀斑的统计研究

根据GOES卫星资料 (1～ 8 ) ,统计了第 2 2太阳活动周 (1986 .9～ 1996 .10 )软X射线耀斑数 ,共计 2 0 930个耀斑 ,其中X级最少 ,不到 1% ;M级为 10 % ;C级最多 ,约占 6 0 % .统计发现 ,此活动周有两个峰 ,分别在 1989年和 1991年 ,1989年平均耀斑指数为 4 2 7,1991年为 4 6 8;C、M及X级耀斑数在活动周的上升期迅速增大 ,两年多时间就达到极大 ;而下降期缓慢减小 ,长达 4年多 ;耀斑发生率随软X射线峰值流量的变化呈幂律谱分布 ,谱指数为 - 2 .135 ,相关系数为- 0 .987;小耀斑易受背景影响 ,B级耀斑以及C级耀斑中的较小者在峰年及其前后往往湮没在背景中 ,无法辨别 .还发现X射线耀斑的光学对应体 (Hα耀斑 )与X射线耀斑的比率随X射线耀斑级别的增高而增大 ,X级的光学对应体达 94 % ,M级为 83% ,C级为 6 3% ,B级只有 30 % .

A Statistical Study of Soft X-ray Flares during Solar Cycle 22

Solar flares are among the most energetic events on the Sun. The eruption of solar flares has a great influence on the space environment and the Earth. A statistical study of flares occurring in a whole solar cycle is important in understanding the main characteristics of flares and useful for further study on the flare mechanism. In this paper, we make a complete statistics of the soft X_ray (SXR) flares during solar Cycle 22 according to the GOES satellite data. Among the 20 930 flares, less than 1% belong to X_class, 10% to M_class, and about 60% to C_class. The flare activity in this cycle undergoes a similar behavior to the sunspot number and experiences two peaks in 1989 and 1991, in which the mean flare index is 427 and 468, respectively. The numbers of flares of C_, M_, and X_classes increase rapidly during the ascending phase of the solar cycle, and decrease slowly during the decay phase. The ascending phase takes only about 2 years while the descending phase more than 4 years. The occurrence ratio of flares has a power_law distribution in dependence on the peak soft X_ray flux; the average power_law index for d N /d F , where N is the number of flares and F is the peak flux, is about -2.135 and the correlation coefficient is -0.987. Smaller (B_class and some C_class) flares are affected by the background noise so that they are not included in the derivation of flare index. Moreover, the percentage of SXR flares that have optical counterparts increases with the soft X_ray flux which amounts to 94% for X_class, 83% for M_class, 63% for C_class, and only 30% for B_class, respectively.