2009年7月22日日全食的日冕结构

Coronal structure at the total solar eclipse 2009-07-22

日冕是太阳的外层大气,其高温等离子体外流而形成太阳风,又发射很强的紫外和X射线辐射,日冕活动严重地影响日地空间环境.日冕结构与太阳活动有密切联系.2009年7月22日发生21世纪最壮观的日全食,是观测研究日冕的良机,但由于全食带地区大多阴雨而受挫,幸好在个别天气好的地方可拍摄到高质量的日冕数码像.本文选取其中部分像,进行数字图像处理,结合SOHO卫星LASCOC2所观测的当天的外冕图像进行分析,揭示日冕的一些结构,得到日冕两极和赤道的亮度径向平滑分布.2009年是第24个太阳活动周期的开始年,虽然太阳活动水平仍较低,但比去年的极小期活跃得多,日冕结构有较明显的变化,不仅显示赤道区比两极区延展,即使东西赤道区和南北极区也有较大差别.赤道东侧的冕流,尤其赤道北的大冕流很显著,南极区比北极区的冕羽由更多的极射线组成.日冕赤道区和极区的亮度径向分布接近于去年的太阳活动极小,但赤道东西方向的亮度分布差别较去年小,南极与北极方向的差别也较小.这些日冕特征也显示在日冕等亮度图上.

Solar corona is the outermost part of the solar atmosphere, from which strong UV and X-ray radiation are emitted. Coronal high temperature plasma outflows and forms the solar wind. Coronal activities influence seriously the space environment between the Sun and the Earth. Coronal structures are closely related with the solar activities. The total solar eclipse at the July 22, 2009, is the best magnificent sight in the 21st century and the best opportunity to observe the corona on ground. However, due to bad weather, most observations in the total eclipse areas were baffled. Fortunately, some images of high quality were taken in a few places with good weather. In this work, a series of images are selected and digital processing is made with the computer. Studying them together with the images of outer corona by SOHO satellite/LASCO C2 at that day, some coronal structures are revealed and radial brightness profiles of the corona in directions of pole and equator of the Sun are measured. The solar cycle 24 began in 2009 and a few sunspots appeared. At this eclipse, coronal structures show more extents in equatorial regions than in polar regions, with differences between east and west and between south and north of the solar disk. Coronal streamers on east of the disk, particularly the largest one in north of the equator are very obvious. Polar rays are more in south polar region than in north polar region. The radial brightness profiles of the corona in directions of pole and equator are rather similar to those at the total eclipse in 2008 and those of the Van de Hulst model in solar minimum. Some features are also shown in the isophote map of the corona.