耀斑和冕环振荡的光谱观测研究

In the observations of solar physics, the flares and coronal loops usually display the behaviors of the oscillations. The typical periods of these oscillations can be ranging from milliseconds through seconds to tens of minutes, the detected wavelengths are also very broad, from radio through visible and extreme-ultraviolet (EUV) to X-ray. Previous observations were mainly deal with the visible, EUV and X-ray images, the radio dynamic spectra or the light curves at the high energy. The most studies were the periods and positions of the oscillations, the delay of the time and phase between different bands. Generally speaking, these oscillations are thought to be modulated by the magnetohydrodynamic (MHD) waves, such as the fast kink and sausage waves, the slow magnetoacoustic waves. Basing on the observations from the IRIS spectra, this project plans to study the spectral behaviors of the flare and coronal loop oscillations, which focus on the changing of the line intensities, Doppler velocities, non-thermal velocities and line widths, and the distribution of the densities. Meantime, we will study the magnetic fields from the SDO/HMI observations, and diagnose the plasmas with the method of DEM analysis. We first study one or two cases about the flare and coronal loop oscillations, and then statistical analysis of a large sample observations basing on the case analysis. We wish to reveal the formation mechanism of the flare and coronal loop oscillations, respectively, and hope to find the similarities and differences between these two oscillations, which maybe contribution to the chromospheric and coronal heating.

在太阳物理的观测研究中，耀斑和冕环经常表现出一些周期性的振荡现象。振荡周期从数十毫秒到几十分钟不等，其观测波段也很广泛，从射电经可见光、极紫外（EUV）直到X射线。以往的观测研究所使用的数据主要集中在可见光、EUV和X射线的成像观测、射电动态频谱以及高能流量曲线等。主要是研究振荡的周期、位置以及不同波段的相位差和时间差等信息。一般认为这些振荡是由MHD波调制的，如快模波（扭结模和腊肠模）、慢磁声波等。本项目则计划利用IRIS卫星的光谱数据来研究耀斑和冕环振荡的光谱表现，重点研究这些振荡的谱线强度、多普勒速度，非热速度和谱线宽度，以及密度分布等信息。同时结合SDO/HMI的成像观测研究振荡区域的磁场情况，利用DEM分析诊断振荡区域的等离子体信息。计划在个例分析的基础上进行大样本的统计分析，预期分别揭示耀斑环振荡和冕环振荡的物理机制，期望找到这两种振荡的异同点，为色球和日冕加热等问题提供参考。

使用IRIS的光谱观测数据，我们研究了两组高温耀斑环中的多普勒速度振荡（Fe XXI），发现它们都属于kink振荡，但分别属于强阻尼kink振荡和弱阻尼的kink振荡。同时结合冕振学和磁场外估算了耀斑爆发期间的日冕磁场强度，结果远大于宁静日冕的磁场强度，这为日冕磁场的测量提供了参考。我们还研究了耀斑辐射过程中的准周期振荡现象，发现振荡周期与辐射能量的光子数有关，说明耀斑辐射期间存在周期性的磁重联。使用NVST的高分辨率观测数据，我们研究了宁静日珥中的小尺度振荡现象，发现它们与日冕中的MHD波有关。结合IRIS光谱和SDO成像的观测数据，我们同时在太阳大气的光球层、色球层和过渡区以及日冕中探测到了小尺度重联事件。我们在耀斑期间和耀斑前兆都发现了非热电子驱动色球蒸发的观测证据。最后，我们对小尺度磁重联进行了二维MHD模拟，得到了与IRIS观测结果一致的光谱外形，说明过渡区爆发事件中的小尺度磁重联是由等离子体不稳定性驱动的。我们的研究结果有助于理解磁场重联、粒子加速、日冕加热等太阳物理中的基本问题。