LASCO White-Light Observations of Eruptive Current Sheets Trailing CMEs
详细信息 查看全文
- 作者：David F. Webb ; Angelos Vourlidas
- 关键词：Sun ; corona ; Sun ; coronal mass ejections ; Magnetic reconnection
- 刊名：Solar Physics
- 出版年：2016
- 出版时间：December 2016
- 年：2016
- 卷：291
- 期：12
- 页码：3725-3749
- 全文大小：
- 刊物类别：Physics and Astronomy
- 刊物主题：Astrophysics and Astroparticles; Atmospheric Sciences; Space Sciences (including Extraterrestrial Physics, Space Exploration and Astronautics);
- 出版者：Springer Netherlands
- ISSN：1573-093X
- 卷排序：291
文摘
Many models of eruptive flares or coronal mass ejections (CMEs) involve formation of a current sheet connecting the ejecting CME flux rope with a magnetic loop arcade. However, there is very limited observational information on the properties and evolution of these structures, hindering progress in understanding eruptive activity from the Sun. In white-light images, narrow coaxial rays trailing the outward-moving CME have been interpreted as current sheets. Here, we undertake the most comprehensive statistical study of CME-rays to date. We use SOHO/LASCO data, which have a higher cadence, larger field of view, and better sensitivity than any previous coronagraph. We compare our results to a previous study of Solar Maximum Mission (SMM) CMEs, in 1984 – 1989, having candidate magnetic disconnection features at the CME base, about half of which were followed by coaxial bright rays. We examine all LASCO CMEs during two periods of minimum and maximum activity in Solar Cycle 23, resulting in many more events, \(\sim130\) CME-rays, than during SMM. Important results include: The occurrence rate of the rays is \(\sim11~\%\) of all CMEs during solar minimum, but decreases to \(\sim7~\%\) at solar maximum; this is most likely related to the more complex coronal background. The rays appear on average 3 – 4 hours after the CME core, and are typically visible for three-fourths of a day. The mean observed current sheet length over the ray lifetime is \(\sim12~R_{\odot}\), with the longest current sheet of \(18.5~R_{\odot}\). The mean CS growth rates are \(188~\mbox{km}\,\mathrm{s}^{-1}\) at minimum and \(324~\mbox{km}\,\mathrm{s}^{-1}\) at maximum. Outward-moving blobs within several rays, which are indicative of reconnection outflows, have average velocities of \(\sim350~\mbox{km}\,\mathrm{s}^{-1}\) with small positive accelerations. A pre-existing streamer is blown out in most of the CME-ray events, but half of these are observed to reform within \(\sim1\) day. The long lifetime and long lengths of the CME-rays challenge our current understanding of the evolution of the magnetic field in the aftermath of CMEs.