非爆发性磁重联在太阳爆发活动中的作用

Solar eruptions, including solar flares, coronal mass ejections and prominence/filament eruptions, are responsible for the most severe space weather impacts on the Earth environment. Recent advances in observation and modeling are illuminating the key physics of the driving mechanisms, but the actual processes leading to the initiation of the eruption remain elusive. Obviously, if we are to succeed in ultimately understanding the physics of solar eruptions, we must identify observationally the key processes in building up the pre-eruption structures and the conditions leading up to their unstablness, so as to provide diagnostic information for comparison with, and incorporation into, the models. Solar eruptions typically begin with a relatively long-lasting, slow-rise phase (often traced by the slow rising of a prominence) and then rather abruptly transition to an explosive, fast-rise phase of rapid acceleration. The absence of pre-eruption brightening has been naturally taken as evidence for ideal MHD instabilities in previous studies. However, our recent observations using data obtained by the Solar Dynamic Observatory (SDO) have demonstrated that nonexplosive reconnection, which progresses steadily and is not directly involved in, but of close relevance to, the subsequent eruption, may occur even before the slow-rise phase. We found that the core-structure of solar eruptions, a flux rope, could form via nonexplosive reconnection, and that it could become unstable with magnetic flux feeding from either chrompospheric fibrils or filaments via, again, nonexplosive reconnection. These processes, however, are often only visible in certain SDO/AIA filters whose temperature ranges are not covered by previous EUV instruments. Therefore, it is crucial that we reexamine our understandings of the physical processes leading to the destabilization of the solar corona by taking advantage of the unprecedented spatiotemporal resolution and temperature coverage provided by SDO. In particular, we propose to explore the nonexplosive reconnection process observed prior to the eruption with a focus on its role in the initiation and triggering of solar eruptions, by combining UV/EUV imaging observation of the solar atmosphere with photospheric magnetic measurements.

以耀斑、日冕物质抛射和日珥爆发为代表的太阳爆发活动是对地球环境造成灾害性影响的极端空间天气事件的主要驱动源。近年来国际上在观测和模拟方面取得了很多进展，但仍不清楚其中的具体物理过程。要最终理解太阳爆发活动的物理机制，必须对爆发前的演化过程进行细致的研究，以证认那些对于爆发结构的形成和触发有关键作用的物理过程，从而为理论建模提供可诊断的信息。申请人应用SDO卫星数据得到的一系列结果表明，太阳爆发活动的核心结构- - 磁通量绳可以形成于爆发前近稳态的磁重联(称为"非爆发性磁重联"），而色球暗条或纤维也可以通过非爆发性磁重联向磁通量绳供给磁通，最终使之不稳定而爆发。由于时空分辨率和温度覆盖范围的欠缺，类似观测在从前常被理解为理想磁流体不稳定性驱动的爆发。因此，本项目提出利用最新的SDO 数据，结合太阳光球磁场的测量和太阳大气的UV/EUV成像观测以深入探索非爆发性磁重联在太阳爆发活动中的作用。

以太阳耀斑、日冕物质抛射和日珥/暗条爆发为代表的太阳爆发活动是对地球环境造成灾害性影响的极端空间天气事件的主要驱动源。近年来国际上在观测和模拟方面取得了很多进展，但是仍不清楚其中的具体物理过程。要最终理解太阳爆发活动的物理机制，我们必须对爆发前的演化过程进行细致的研究，以证认那些对于爆发结构的形成和触发有关键作用的物理过程。本项目旨在系统地研究爆发前的演化和动力学过程，以证认形成爆发结构重要因素和触发机制，深入理解爆发前磁重联与爆发的联系，为理论模型提供有用的约束条件和诊断信息。经过四年探索，项目组对于日冕物质抛射的前身结构——磁绳——及其向爆发阶段的演化过程有了更加深入的认识：发展了计算磁挤压因子和磁螺绕数的方法，提出在三维磁场中客观证认磁绳的判据；提出了通过色球观测研究磁绳演化的新思路，取得日冕磁绳动态形成在日面响应的观测证据，并据此推断其内部磁场的扭缠分布；通过统计研究得到磁绳不稳定性临界高度的经验公式；揭示多磁绳系统及其内部的磁重联可能是导致行星际复杂抛射物的原因。同时，本项目的探索还推进了对三维磁重联在太阳爆发活动中的作用的理解。项目期间共发表标注本基金的SCI论文36篇，其中以项目负责人为第一或通讯作者的SCI论文13篇。