热起始耀斑前兆事件中的等离子体加热与能量化
Plasma Heating and Energization in Hot-Onset Flare Precursor Events
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中文总结 AI 辅助
该研究通过磁重联模拟揭示引导场演化导致两种能量化机制，自洽解释了太阳耀斑热起始阶段先于非热辐射的现象。
中文摘要 AI 辅助
近期对太阳耀斑的观测揭示了一个在脉冲相之前出现的明显“热起始”阶段，其特征是等离子体温度升高（>10 MK）、发射测量稳定增加，以及未检测到非热辐射。标准耀斑模型将热耀斑等离子体的形成归因于由非热电子能量沉积驱动的色球蒸发，因此无法自然解释为何热加热先于非热辐射。受近期双带耀斑中引导场演化观测以及大规模磁流体动力学模拟的启发，我们利用动力学宏观尺度模型kglobal，在空间非均匀引导场初始条件下进行磁重联模拟，研究热起始能量化过程。由于费米加速产生的电子非热能效率随引导场强度降低而减弱，演化的引导场产生了两种截然不同的能量化机制。在初始高引导场阶段，体电子温度升至约初始值的两倍，而非热粒子产生仍较弱。进入低引导场机制后，高能粒子产生显著增强，高能电子群体迅速增长。这些发现为热起始提供了自洽的物理解释，表明引导场的宏观演化自然衔接了太阳耀斑的热起始相和脉冲相，无需单独的触发机制。
英文摘要
Recent observations of solar flares have revealed a distinct 'hot onset' phase preceding the impulsive phase, characterized by elevated plasma temperature (>10 MK), a steady increase in emission measure, and the absence of detectable nonthermal emission. The standard flare model attributes the formation of hot flare plasma to chromospheric evaporation driven by energy deposition from nonthermal electrons, and therefore does not naturally explain why thermal heating precedes nonthermal emission. Motivated by recent observations of guide-field evolution in two-ribbon flares and by large-scale MHD simulations, we investigate hot-onset energization using simulations of magnetic reconnection with the kinetic macroscale model kglobal initialized with a spatially non-uniform guide field. Because the efficiency of electron non-thermal energy production from Fermi acceleration decreases with guide-field strength, the evolving guide field produces two distinct energization regimes. During the initial high-guide-field phase, the bulk electron temperature rises to approximately twice its initial value, while non-thermal particle production remains weak. Upon entering the low-guide-field regime, energetic particle production is significantly enhanced, with the population of high-energy electrons growing rapidly. These findings provide a self-consistent physical explanation for the hot onset, demonstrating that the macroscopic evolution of the guide field naturally bridges the hot-onset and impulsive phases of solar flares without requiring a separate trigger mechanism.
发表机构
- IREAP, University of Maryland（马里兰大学 IREAP）
- Dept. of Physics, Institute for Physical Science and Technology, and the Joint Space Science Institute, University of Maryland（马里兰大学物理系、物理科学与技术研究所和联合空间科学研究所）
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