太阳大气磁流管中腊肠模的磁震学研究

Sausage modes are one of the infinitely many collective wave modes supported by magnetized structures in the solar atmosphere. They are the primary mechanism employed for interpreting second-scale quasi-periodic-pulsations in the lightcurves of solar flares, and their measurements can be used to infer such key information as the magnetic field strength in flare loops. Recent observations indicate that sausage modes abound in photospheric and chromospheric structures, and propagating sausage waves may be an important energy supplier to account for chromospheric heating. However, the interpretations of available measurements tend to be based on theories whose assumptions are far from reality. In the framework of Magnetohydrodynamics, we will systematically examine sausage modes in magnetized structures in the solar atmosphere, paying special attention to flare loops and photospheric pores. We will account for the effects of finite plasma beta, the continuous transverse distribution of the physical parameters, as well as longitudinal stratification. These factors are crucial for characterizing realistic atmospheric structures. We will assess how these factors influence the propagation and damping of propagating sausage waves, and how they impact the inference of atmospheric parameters based on sausage mode measurements. We will be able to evaluate the uncertainties of the available inference of the parameters of flare loops, and we will also address whether sausage waves in photospheric pores can carry a sufficient energy flux to heat the chromosphere. The outcome of the project will also be applicable to the abundant measurements of sausage modes in photospheric and chromospheric waveguides.

腊肠模是太阳大气磁结构中集体波模的一种。它是耀斑光变曲线中周期在秒量级的准周期脉动的主要解释机制，其观测可用以推测耀斑环磁场强度等关键信息。近期观测还发现光球及色球磁结构中普遍存在腊肠模，且腊肠行波可能对色球加热起重要贡献。已有腊肠模观测的理论理解过于简化，未考虑耀斑环和光球及色球磁结构的现实特征。本项目拟利用磁流体力学理论，系统讨论耀斑环、光球气孔等典型太阳大气磁结构中的腊肠模，计入有限热压磁压比(即等离子体beta)、磁管介质参数的横向连续分布、管内外介质的纵向非均匀性这三个关键的现实因素，考察现实因素怎样影响腊肠行波的传播及衰减，探讨其对基于腊肠模的太阳大气参数诊断的影响。所得理论结果将厘清已有耀斑环参数诊断实践的不确定性，并回答光球气孔中腊肠行波能否携带足够能量以提供色球加热这一疑问，还将对光球和色球中腊肠模的观测提供更坚实的物理理解。

腊肠模是太阳大气磁结构中集体波模的一种。它是耀斑光变曲线中周期在秒量级的准周期脉动的主要解释机制，其观测可用以推测耀斑环磁场强度等关键信息。近期观测还发现光球及色球磁结构中普遍存在腊肠模，且腊肠行波可能对色球加热起重要贡献。已有腊肠模观测的理论理解过于简化，未考虑耀斑环和光球及色球磁结构的现实特征。该项目对耀斑环和光球气孔等典型太阳大气磁结构中的腊肠模进行了系统的理论研究，计入有限beta和磁管介质参数的横向分布这两个关键的现实因素，考察了现实因素怎样影响腊肠波的衰减，关注其对基于腊肠模的磁震学应用的影响，以及光球气孔中腊肠行波能否携带足够能量以提供色球加热这一问题。. 研究结果表明：磁片参数横向连续分布的细节对快波的周期和衰减时间影响最大；相比而言，对大部分日冕磁片，如果快波的周期和衰减时间以片内横向快波时间来衡量，热压的影响几乎可以忽略。这不仅给出了有限beta情形下冕震学的实践简化，还评估了有限beta和参数横向连续分布这两个现实因素的相对重要性，从而为未来的冕震学应用和观测数据分析奠定了理论基础。其次，对于光球中慢腊肠表面波的衰减，直接电阻阻尼比cusp共振吸收更有效。因此，在考察光球气孔中腊肠行波能否携带足够能量以提供色球加热这一问题时，共振吸收这一理想机制的贡献几乎可以忽略，直接电阻阻尼，以及可能的双极扩散和热传导等，会对色球加热提供更大的贡献。. 项目预期外的收获有二。一是从数值和解析的角度讨论了日冕磁片和磁环中束缚腊肠波列的观测特征，并给出了相应的理论解释，从而可以基于高时间分辨观测数据来推断结构中亚分辨率的密度分布信息，而这一点与基于波动的日冕加热机制效率密切相关。二是基于IRIS探测器的空间和光谱分辨，正演分析某一视线方向的辐射强度、多普勒速度和多普勒展宽等可观测量，考察非平衡电离对观测量的可能影响，为准确证认腊肠模提供了更为详尽的判据。