中性电流片的形成和环形日冕瞬变

在双极背景场下,光球层反向磁通量的喷发将会在新老磁场之间形成中性电流片.本文从理想磁流体方程组出发,考虑磁场和日冕等离子体的相互作用,对上述电流片的形成过程进行了数值研究.结果表明,对亚音速喷发,将由里向外形成四个区域:(1)由喷发物质直接形成的低温,高密度日珥,位于最里层;(2)紧挨抛射日珥的低温稀疏区;(3)喷发物质和日冕物质向中性电流片集中形成的高温.高密度物质环;(４)在环的周围,由快磁声波形成的,密度略比日冕背景为高的前鞘区.上述结构与典型的环形日冕瞬变的观测特征相符.由此表明双极背景场下反向磁通量的喷发可能是触发这类瞬变的重要机制. 

The Formation of Neutral Current Sheets and the Associated Loop Coronal Transients

Under a bipolar background magnetic field, a neutral current sheet is liable to form in between the new emerging magnetic field and the background owing to an eruption of opposite magnetic flux. Based on the ideal magnetohydrodynamic equations, this paper has made a numerical study of the above Formation of current sheets, considering the interaction between the magnetic field and the coronal plasma. The result shows that a subsonic eruption gives rise to a four-region structure from inside to outside: (1) a low-temperature, high-density prominence, consisting of the erupted material and located at the most-interior-region, (2) a low-temperature rarefaction region right next to the erupted prominence, (3) a high-temperature, high-density loop formed by the concentration of both erupted and coronal material into the neutral current sheet, and (4) a forerunner around the loop with the density slightly higher than the coronal background, due to the fast magnetosonic wave. The above mentioned structure is conformed with the observed features of typical loop coronal transients. Consequently, the eruption of opposite magnetic flaxes under the bipolar background field is most likely an important mechanism for triggering such kind of transients.